What is the CVSS score of CVE-2026-41887?

CVE-2026-41887 has a CVSS 3.1 base score of 4.9 (Medium). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N. EPSS exploitation probability: 0.0%.

Is there a patch available for CVE-2026-41887?

Yes, a patch is available for CVE-2026-41887. Update the affected software to the latest version immediately.

Flarum CVE-2026-41887

EUVD-2026-28804 MEDIUM

Path Traversal (CWE-22)

2026-05-08 GitHub_M

SSRF PHP Path Traversal

4.9

CVSS 3.1 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

4.9 MEDIUM

AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N

Primary rating from GitHub Advisory · only source for this CVE.

CVSS VectorGitHub Advisory

CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N

Attack Vector

Network

Attack Complexity

Low

Privileges Required

High

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

None

Availability

None

Lifecycle Timeline

Patch available

May 08, 2026 - 18:03 EUVD

Source Code Evidence Fetched

May 08, 2026 - 17:00 vuln.today

Analysis Generated

May 08, 2026 - 17:00 vuln.today

CVE Published

May 08, 2026 - 15:50 nvd

MEDIUM 4.9

DescriptionGitHub Advisory

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.

AnalysisAI

Authenticated administrators in Flarum can read arbitrary files and trigger server-side request forgery via LESS injection in theme color settings. The vulnerability exploits an incomplete patch for CVE-2023-27577 that restricted @import and data-uri() only in the custom_less setting but failed to apply the same restrictions to other LESS config variables such as theme_primary_color and theme_secondary_color. An attacker with admin credentials can inject arbitrary @import directives into compiled forum.css, exposing sensitive files or making outbound HTTP requests to internal networks and cloud metadata endpoints. Vendor-released patches: Flarum 1.8.16 and 2.0.0-rc.1.

Technical ContextAI

Flarum uses LESS (Leaner Style Sheets), a CSS preprocessor that supports @import directives and data-uri() functions. The vulnerability stems from the fact that theme color settings and any custom LESS config variables registered via Extend\Settings::registerLessConfigVar() are interpolated verbatim into LESS source code at compile time without sanitization. The underlying LESS parser honors @import (inline) '<path>' syntax, which allows file inclusion and HTTP requests. The previous patch for CVE-2023-27577 only validated the custom_less setting itself but neglected to apply the same validation to other settings that feed into LESS compilation. This is a path traversal and SSRF vulnerability (CWE-22) enabled by insufficient input validation on LESS preprocessor features.

RemediationAI

Vendor-released patch: Flarum 1.8.16 for the 1.x branch and 2.0.0-rc.1 for the 2.x branch. Upgrade via composer update flarum/core to the patched versions immediately. The fix extends the existing @import and data-uri() validation to all settings registered as LESS config variables, not just custom_less. If immediate upgrade is not possible, the primary workaround is to restrict admin account privileges and enforce strong, unique passwords to prevent account compromise; however, this does not prevent exploitation by legitimately trusted administrators. Alternative mitigations include disabling theme customization features temporarily (if the forum software permits) or restricting the PHP process to a read-only filesystem root to limit local file inclusion impact, though this requires careful testing and may affect forum functionality. See https://github.com/flarum/framework/commit/2d90a1f19f0e46f8c7e1b07c48ba74b5e38f8410 for technical patch details.