Description
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: 2026-05-08
Score: 4.9 Medium
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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Tracking

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Advisories
Source ID Title
Github GHSA Github GHSA GHSA-xjvc-pw2r-6878 Flarum: Path traversal in LESS parser via theme color settings (incomplete fix for CVE-2023-27577)
History

Sun, 10 May 2026 21:45:00 +0000

Type Values Removed Values Added
First Time appeared Flarum
Flarum framework
Vendors & Products Flarum
Flarum framework

Fri, 08 May 2026 20:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Fri, 08 May 2026 16:30:00 +0000

Type Values Removed Values Added
Description 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.
Title Flarum: Path traversal in LESS parser via theme color settings (incomplete fix for CVE-2023-27577)
Weaknesses CWE-22
CWE-918
References
Metrics cvssV3_1

{'score': 4.9, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N'}


Subscriptions

Flarum Framework
cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-05-08T19:26:53.642Z

Reserved: 2026-04-22T15:11:54.671Z

Link: CVE-2026-41887

cve-icon Vulnrichment

Updated: 2026-05-08T19:23:44.211Z

cve-icon NVD

Status : Deferred

Published: 2026-05-08T17:16:30.890

Modified: 2026-05-12T16:45:18.893

Link: CVE-2026-41887

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-05-10T21:25:04Z

Weaknesses