{ "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-2026-34730", "tracking": { "current_release_date": "2026-04-03T15:31:08.169346Z", "generator": { "date": "2026-02-17T15:00:00Z", "engine": { "name": "V.E.L.M.A", "version": "1.7" } }, "id": "CVE-2026-34730", "initial_release_date": "2026-04-01T23:02:30.235670Z", "revision_history": [ { "date": "2026-04-01T23:02:30.235670Z", "number": "1", "summary": "CVE created.| Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| References created (2).| CWES updated (1)." }, { "date": "2026-04-01T23:02:42.553833Z", "number": "2", "summary": "NCSC Score created." }, { "date": "2026-04-02T19:03:28.549932Z", "number": "3", "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| Products created (1).| References created (3).| CWES updated (1)." }, { "date": "2026-04-02T19:03:36.906663Z", "number": "4", "summary": "NCSC Score updated." }, { "date": "2026-04-02T20:10:10.189879Z", "number": "5", "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| References created (3).| CWES updated (1)." }, { "date": "2026-04-02T20:10:12.182049Z", "number": "6", "summary": "NCSC Score updated." }, { "date": "2026-04-03T07:35:15.656378Z", "number": "7", "summary": "NCSC Score updated." }, { "date": "2026-04-03T13:39:24.991765Z", "number": "8", "summary": "Unknown change." }, { "date": "2026-04-03T13:39:32.645118Z", "number": "9", "summary": "NCSC Score updated." }, { "date": "2026-04-03T15:31:07.043306Z", "number": "10", "summary": "Source connected.| CVE status created. (valid)| EPSS created." } ], "status": "interim", "version": "10" } }, "product_tree": { "branches": [ { "branches": [ { "branches": [ { "category": "product_version_range", "name": "vers:unknown/<9.14.1", "product": { "name": "vers:unknown/<9.14.1", "product_id": "CSAFPID-5985269" } } ], "category": "product_name", "name": "copier" } ], "category": "vendor", "name": "copier-org" } ] }, "vulnerabilities": [ { "cve": "CVE-2026-34730", "cwe": { "id": "CWE-22", "name": "Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')" }, "notes": [ { "category": "description", "text": "### Summary\n\nCopier's `_external_data` feature allows a template to load YAML files using template-controlled paths. The documentation describes these values as relative paths from the subproject destination, so relative paths themselves appear to be part of the intended feature model.\n\nHowever, the current implementation also allows destination-external reads, including:\n\n- Parent-directory paths such as `../secret.yml`\n- Absolute paths such as `/tmp/secret.yml`\n\nand then exposes the parsed contents in rendered output.\n\nThis is possible without `--UNSAFE`, which makes the behavior potentially dangerous when Copier is run against untrusted templates. I am not certain this is unintended behavior, but it is security-sensitive and appears important to clarify.\n\n### Details\n\nThe relevant flow is:\n\n1. A template defines `_external_data`\n2. Copier renders the configured path string\n3. Copier calls `load_answersfile_data(dst_path, rendered_path, warn_on_missing=True)`\n4. `load_answersfile_data()` opens `Path(dst_path, answers_file)` directly\n5. Parsed YAML becomes available as `_external_data.` during rendering\n\nRelevant code:\n\n- \n- \n\nThe sink is:\n\n```python\nwith Path(dst_path, answers_file).open(\"rb\") as fd:\n return yaml.safe_load(fd)\n```\n\nThere is no containment check to ensure the resulting path stays inside the subproject destination.\n\nThis is notable because Copier already blocks other destination-escape paths. Normal render-path traversal outside the destination is expected to raise `ForbiddenPathError`, and that behavior is explicitly covered by existing tests in . `_external_data` does not apply an equivalent containment check.\n\nThe public documentation describes `_external_data` values as relative paths \"from the subproject destination\" in , with examples using `.copier-answers.yml` and `.secrets.yaml`. That clearly supports relative-path usage, but it does not clearly communicate that a template may escape the destination with `../...` or read arbitrary absolute paths. Because this behavior also works without `--UNSAFE`, it seems worth clarifying whether destination-external reads are intended, and if so, whether they should be documented as security-sensitive behavior.\n\n### PoC\n\n#### PoC 1: `_external_data` reads outside the destination with `../`\n\n```sh\nmkdir src dst\necho 'token: topsecret' > secret.yml\n\nprintf '%s\\n' '_external_data:' ' secret: ../secret.yml' > src/copier.yml\nprintf '%s\\n' '{{ _external_data.secret.token }}' > src/leak.txt.jinja\n\ncopier copy --overwrite src dst\ncat dst/leak.txt\n```\n\nExpected output:\n\n```text\ntopsecret\n```\n\n#### PoC 2: `_external_data` reads an absolute path\n\n```sh\nmkdir abs-src abs-dst\necho 'token: abssecret' > absolute-secret.yml\n\nprintf '%s\\n' '_external_data:' \" secret: $(pwd)/absolute-secret.yml\" > abs-src/copier.yml\nprintf '%s\\n' '{{ _external_data.secret.token }}' > abs-src/leak.txt.jinja\n\ncopier copy --overwrite abs-src abs-dst\ncat abs-dst/leak.txt\n```\n\nExpected output:\n\n```text\nabssecret\n```\n\n### Impact\n\nIf untrusted templates are in scope, a malicious template can read attacker-chosen YAML-parseable local files that are accessible to the user running Copier and expose their contents in rendered output.\n\nPractical impact:\n\n- Destination-external local file read\n- Disclosure of YAML/JSON/plain-text-like secrets if they parse successfully under `yaml.safe_load`\n- Possible without `--UNSAFE`", "title": "github - https://api.github.com/advisories/GHSA-hgjq-p8cr-gg4h" }, { "category": "description", "text": "Copier is a library and CLI app for rendering project templates. Prior to version 9.14.1, Copier's _external_data feature allows a template to load YAML files using template-controlled paths. If untrusted templates are in scope, a malicious template can read attacker-chosen YAML-parseable local files that are accessible to the user running Copier and expose their contents in rendered output. This issue has been patched in version 9.14.1.", "title": "cveprojectv5 - https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/34xxx/CVE-2026-34730.json" }, { "category": "description", "text": "Copier is a library and CLI app for rendering project templates. Prior to version 9.14.1, Copier's _external_data feature allows a template to load YAML files using template-controlled paths. If untrusted templates are in scope, a malicious template can read attacker-chosen YAML-parseable local files that are accessible to the user running Copier and expose their contents in rendered output. This issue has been patched in version 9.14.1.", "title": "nvd - https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2026-34730" }, { "category": "other", "text": "0.00011", "title": "EPSS" }, { "category": "other", "text": "3.7", "title": "NCSC Score" }, { "category": "other", "text": "The value of the most recent CVSS (V3) score, There is cwe data available from source Nvd", "title": "NCSC Score top decreasing factors" } ], "product_status": { "known_affected": [ "CSAFPID-5985269" ] }, "references": [ { "category": "external", "summary": "Source - github", "url": "https://api.github.com/advisories/GHSA-hgjq-p8cr-gg4h" }, { "category": "external", "summary": "Source - cveprojectv5", "url": "https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/34xxx/CVE-2026-34730.json" }, { "category": "external", "summary": "Source - nvd", "url": "https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2026-34730" }, { "category": "external", "summary": "Source - first", "url": "https://api.first.org/data/v1/epss?limit=10000&offset=0" }, { "category": "external", "summary": "Reference - cveprojectv5; github; nvd", "url": "https://github.com/copier-org/copier/security/advisories/GHSA-hgjq-p8cr-gg4h" }, { "category": "external", "summary": "Reference - github", "url": "https://github.com/advisories/GHSA-hgjq-p8cr-gg4h" }, { "category": "external", "summary": "Reference - cveprojectv5; nvd", "url": "https://github.com/copier-org/copier/commit/5413062eb17b73dc885f5e645cdc161e69ef641b" }, { "category": "external", "summary": "Reference - cveprojectv5; nvd", "url": "https://github.com/copier-org/copier/releases/tag/v9.14.1" } ], "scores": [ { "cvss_v3": { "version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N", "baseScore": 5.5, "baseSeverity": "MEDIUM" }, "products": [ "CSAFPID-5985269" ] } ], "title": "CVE-2026-34730" } ] }