CVE-2026-41887

CVE-2026-41887 · Flarum: Path traversal in LESS parser via theme color settings (incomplete fix for CVE-2023-27577)

This page contains facts from public vulnerability sources. Check the original advisory before updating.

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.

CVSS 4.9 · Medium · EPSS 0.5% · Fix available

Published

2026-05-08T15:50:38.484Z

Updated

2026-05-08T19:26:53.642Z

Stack: php

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