CVE-2026-41887
Flarum: Path traversal in LESS parser via theme color settings (incomplete fix for CVE-2023-27577)
Impact
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.
Affected packages
| Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|
| composer | flarum/core | <= 1.8.15 | 1.8.16 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-xjvc-pw2r-6878
- https://github.com/flarum/framework/security/advisories/GHSA-vhm8-wwrf-3gcw
- https://github.com/flarum/framework/security/advisories/GHSA-xjvc-pw2r-6878
- https://nvd.nist.gov/vuln/detail/CVE-2023-27577
- https://github.com/flarum/framework/commit/2d90a1f19f0e46f8c7e1b07c48ba74b5e38f8410
- https://github.com/flarum/framework/releases/tag/v1.8.16
- https://github.com/flarum/framework/releases/tag/v2.0.0-rc.1
- https://nvd.nist.gov/vuln/detail/CVE-2026-41887