{"id":"CVE-2026-41887","aliases":["GHSA-xjvc-pw2r-6878"],"url":"https://o3.security/vulnerability/CVE-2026-41887","summary":"Flarum: Path traversal in LESS parser via theme color settings (incomplete fix for CVE-2023-27577)","details":"Flarum is open-source forum software. Prior to versions 1.8.16 and 2.0.0-rc.1, Flarum's patch for CVE-2023-27577 restricted the @import and data-uri() LESS features in the custom_less setting, but the same restriction was never applied to other settings registered as LESS config variables (for example theme_primary_color and theme_secondary_color, as well as any key registered via Extend\\Settings::registerLessConfigVar()). Those values are interpolated verbatim into the LESS source at compile time, allowing an authenticated administrator to craft a theme-color value that injects an arbitrary @import directive into the compiled forum.css. Because the underlying LESS parser honours @import (inline) '<path>', an attacker can read arbitrary files reachable by the PHP process (local file inclusion) or trigger outbound HTTP(S) requests (server-side request forgery). This issue has been patched in versions 1.8.16 and 2.0.0-rc.1.","published":"2026-05-08T15:50:38.484Z","modified":"2026-08-07T11:51:04.619998935Z","cvss":{"score":4.9,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N"},"epss":null,"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Packagist","name":"flarum/core","fixedVersion":"1.8.16"},{"ecosystem":"Packagist","name":"flarum/core","fixedVersion":"2.0.0-rc.1"}],"fix":{"url":"https://github.com/flarum/framework/commit/2d90a1f19f0e46f8c7e1b07c48ba74b5e38f8410","label":"flarum/framework@2d90a1f"},"references":[{"type":"WEB","url":"https://github.com/flarum/framework/releases/tag/v1.8.16"},{"type":"WEB","url":"https://github.com/flarum/framework/releases/tag/v2.0.0-rc.1"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/41xxx/CVE-2026-41887.json"},{"type":"ADVISORY","url":"https://github.com/flarum/framework/security/advisories/GHSA-xjvc-pw2r-6878"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-41887"},{"type":"FIX","url":"https://github.com/flarum/framework/commit/2d90a1f19f0e46f8c7e1b07c48ba74b5e38f8410"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-07T11:51:04.619998935Z"}}