{ "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-2026-21861", "tracking": { "current_release_date": "2026-04-01T23:29:50.287703Z", "generator": { "date": "2026-02-17T15:00:00Z", "engine": { "name": "V.E.L.M.A", "version": "1.7" } }, "id": "CVE-2026-21861", "initial_release_date": "2026-03-31T01:25:33.769366Z", "revision_history": [ { "date": "2026-03-31T01:25:33.769366Z", "number": "1", "summary": "CVE created.| Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| References created (3).| CWES updated (1)." }, { "date": "2026-03-31T01:25:35.113818Z", "number": "2", "summary": "NCSC Score created." }, { "date": "2026-03-31T01:38:47.058355Z", "number": "3", "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| Products connected (1).| References created (3).| CWES updated (1)." }, { "date": "2026-03-31T01:38:49.465517Z", "number": "4", "summary": "NCSC Score updated." }, { "date": "2026-03-31T07:35:09.111956Z", "number": "5", "summary": "NCSC Score updated." }, { "date": "2026-03-31T14:38:59.901220Z", "number": "6", "summary": "Unknown change." }, { "date": "2026-03-31T17:25:06.497927Z", "number": "7", "summary": "Source connected.| CVE status created. (valid)| EPSS created." }, { "date": "2026-03-31T17:25:09.435903Z", "number": "8", "summary": "NCSC Score updated." }, { "date": "2026-03-31T23:07:45.940117Z", "number": "9", "summary": "Source created.| CVE status created. (valid)| Description created for source.| CVSS created.| References created (5).| CWES updated (1)." }, { "date": "2026-03-31T23:07:54.662172Z", "number": "10", "summary": "NCSC Score updated." }, { "date": "2026-04-01T23:25:39.690029Z", "number": "11", "summary": "Products connected (1).| Product Identifiers created (1).| Exploits created (1)." }, { "date": "2026-04-01T23:25:46.866336Z", "number": "12", "summary": "NCSC Score updated." } ], "status": "interim", "version": "12" } }, "product_tree": { "branches": [ { "branches": [ { "branches": [ { "category": "product_version_range", "name": "vers:unknown/<5.2.3", "product": { "name": "vers:unknown/<5.2.3", "product_id": "CSAFPID-5982832", "product_identification_helper": { "cpe": "cpe:2.3:a:basercms:basercms:*:*:*:*:*:*:*:*" } } } ], "category": "product_name", "name": "baserCMS" } ], "category": "vendor", "name": "baserCMS" }, { "branches": [ { "branches": [ { "category": "product_version_range", "name": "vers:unknown/<5.2.3", "product": { "name": "vers:unknown/<5.2.3", "product_id": "CSAFPID-5966272" } } ], "category": "product_name", "name": "basercms" } ], "category": "vendor", "name": "baserproject" } ] }, "vulnerabilities": [ { "cve": "CVE-2026-21861", "cwe": { "id": "CWE-78", "name": "Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')" }, "notes": [ { "category": "description", "text": "baserCMS is a website development framework. Prior to version 5.2.3, baserCMS contains an OS command injection vulnerability in the core update functionality. An authenticated administrator can execute arbitrary OS commands on the server due to improper handling of user-controlled input that is directly passed to exec() without sufficient validation or escaping. This issue has been patched in version 5.2.3.", "title": "nvd - https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2026-21861" }, { "category": "description", "text": "baserCMS is a website development framework. Prior to version 5.2.3, baserCMS contains an OS command injection vulnerability in the core update functionality. An authenticated administrator can execute arbitrary OS commands on the server due to improper handling of user-controlled input that is directly passed to exec() without sufficient validation or escaping. This issue has been patched in version 5.2.3.", "title": "cveprojectv5 - https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/21xxx/CVE-2026-21861.json" }, { "category": "description", "text": "## Summary\n\nIn the core update functionality of baserCMS, some parameters sent from the admin panel are passed to the `exec()` function without proper validation or escaping. This issue allows **an authenticated CMS administrator to execute arbitrary OS commands on the server (Remote Code Execution, RCE)**.\n\nThis vulnerability is not a UI-level issue such as screen manipulation or lack of CSRF protection, but rather stems from **a design that directly executes input values received on the server side as OS commands**. Therefore, even if buttons are hidden in the UI, or even if CakePHP's CSRF/FormProtection (SecurityComponent) ensures that only legitimate POST requests are accepted, **an attack is possible as long as a request containing a valid token is processed within an administrator session**.\n\n---\n\n## Vulnerability Information\n\n| Item | Details |\n| ---- | ------- |\n| CWE | CWE-78: Improper Neutralization of Special Elements used in an OS Command |\n| Impact | Remote Code Execution (RCE) |\n| Severity | Critical |\n| Attack Requirements | Administrator privileges required |\n| Reproducibility | Reproducible (confirmed multiple times) |\n| Test Environment | baserCMS 5.2.2 (Docker / development environment) |\n\n---\n\n## Affected Areas\n\n- **Controller**\n - `PluginsController::get_core_update()`\n- **Service**\n - `PluginsService::getCoreUpdate()`\n- **Affected Endpoint**\n - `/baser/admin/baser-core/plugins/get_core_update`\n\n---\n\n## Technical Details\n\n### Vulnerable Code Flow\n\n```text\nPluginsController::get_core_update()\n ↓ Retrieves php parameter from POST data\nPluginsService::getCoreUpdate($targetVersion, $php, $force)\n ↓ Concatenates $php into command string without validation or escaping\nexec($command)\n```\n\n### Relevant Code (Excerpt)\n\n**PluginsController.php**\n\n```php\n$service->getCoreUpdate(\n $request->getData('targetVersion') ?? '',\n $request->getData('php') ?? 'php',\n $request->getData('force'),\n);\n```\n\n**PluginsService.php**\n\n```php\n$command = $php . ' ' . ROOT . DS . 'bin' . DS . 'cake.php composer ' .\n $targetVersion . ' --php ' . $php . ' --dir ' . TMP . 'update';\n\nexec($command, $out, $code);\n```\n\nThe `$php` parameter is user input, and **none** of the following countermeasures are in place:\n\n- Restriction via allowlist\n- Validation via regular expression\n- Escaping via `escapeshellarg()` or similar\n\n---\n\n## Attack Scenario\n\n1. The attacker logs in as a CMS administrator\n2. Sends a POST request to the core update functionality in the admin panel\n3. Specifies a string containing OS commands in the `php` parameter\n4. `exec()` is executed on the server side, running the arbitrary OS command\n\n### Example Attack Input (Conceptual)\n\n```text\nphp=php;id>/tmp/rce_test;#\n```\n\n---\n\n## Verification Results (PoC)\n\n### Execution Result\n\n```bash\n$ docker exec bc-php cat /tmp/rce_test\nuid=1000(www-data) gid=1000(www-data) groups=1000(www-data)\n```\n\nThe above confirms that OS commands can be executed with `www-data` privileges.\n\n### Additional Notes\n\n- Reproducible through the legitimate flow in the admin panel (browser)\n- Succeeds even with CSRF/FormProtection tokens included in a legitimate request\n- Failure cases (400/403) have also been investigated and differentiated\n- Confirmed reproducible via resending HTTP requests with tools such as curl (resending the same request containing valid tokens)\n\n---\n\n## Impact\n\nIf this vulnerability is exploited, the following becomes possible:\n\n- Retrieval of server information\n- Reading/writing arbitrary files\n- Retrieval of application configuration information (DB credentials, etc.)\n- OS-level operations beyond application permission boundaries\n\nAlthough administrator privileges are required, **this is a design issue where the impact extends from the application layer to the OS layer**, and the impact is considered significant.\n\n---\n\n## Recommended Fix\n\n### Primary Recommendation\n\n- Do not accept the PHP executable path from user input\n- Fix the PHP executable on the server side using the `PHP_BINARY` constant\n\n```php\n$php = escapeshellarg(PHP_BINARY);\n```\n\n### Supplementary Fix Recommendations\n\n- Apply `escapeshellarg()` escaping to other command-line arguments (version number, directory, etc.) as well\n- If possible, consider using execution methods that do not involve shell interpretation (array format, Process class, etc.)\n\n### Alternative (Not Recommended)\n\n- Allowlist validation for the PHP executable path\n- Combined use of regex validation and `escapeshellarg()`\n\nHowever, **from the perspective of reducing the attack surface, a design that eliminates user input entirely is recommended**.\n\n---\n\n## Additional Notes\n\n- This issue is independent of UI display controls (showing/hiding buttons)\n- As long as the endpoint exists, an attack is possible if a request containing valid tokens is processed\n- This is a problem stemming from the design-level handling of input, and cannot be prevented by CSRF or UI controls alone\n\n---\n\n## Conclusion\n\nDue to a design issue in baserCMS's core update functionality where user input is passed to `exec()` without validation, **Remote Code Execution (RCE) is achievable with administrator privileges**. This vulnerability can be fixed through input validation and design review, and prompt remediation is recommended.\n\nThis advisory was translated from Japanese to English using GitHub Copilot.", "title": "github - https://api.github.com/advisories/GHSA-qxmc-6f24-g86g" }, { "category": "other", "text": "0.00174", "title": "EPSS" }, { "category": "other", "text": "3.6", "title": "NCSC Score" }, { "category": "other", "text": "Is related to (a version of) an uncommon product, There is exploit data available from source Nvd, Is related to an uncommon product vendor, Exploit code publicly available", "title": "NCSC Score top decreasing factors" } ], "product_status": { "known_affected": [ "CSAFPID-5966272", "CSAFPID-5982832" ] }, "references": [ { "category": "external", "summary": "Source - nvd", "url": "https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2026-21861" }, { "category": "external", "summary": "Source - cveprojectv5", "url": "https://raw.githubusercontent.com/CVEProject/cvelistV5/main/cves/2026/21xxx/CVE-2026-21861.json" }, { "category": "external", "summary": "Source - first", "url": "https://api.first.org/data/v1/epss?limit=10000&offset=0" }, { "category": "external", "summary": "Source - github", "url": "https://api.github.com/advisories/GHSA-qxmc-6f24-g86g" }, { "category": "external", "summary": "Reference - cveprojectv5; github; nvd", "url": "https://basercms.net/security/JVN_20837860" }, { "category": "external", "summary": "Reference - cveprojectv5; github; nvd", "url": "https://github.com/baserproject/basercms/releases/tag/5.2.3" }, { "category": "external", "summary": "Reference - cveprojectv5; github; nvd", "url": "https://github.com/baserproject/basercms/security/advisories/GHSA-qxmc-6f24-g86g" }, { "category": "external", "summary": "Reference - github", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-21861" }, { "category": "external", "summary": "Reference - github", "url": "https://github.com/advisories/GHSA-qxmc-6f24-g86g" } ], "scores": [ { "cvss_v3": { "version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H", "baseScore": 9.1, "baseSeverity": "CRITICAL" }, "products": [ "CSAFPID-5966272", "CSAFPID-5982832" ] } ], "title": "CVE-2026-21861" } ] }