CVE-2026-41887: Flarum LFI and SSRF via LESS theme settings injection

CVE-2026-41887 · Severity: medium · CVSS 4.9 · Published 2026-05-08

Flarum is an open-source forum platform. A security flaw allows an authenticated administrator to read sensitive files from the server or access internal network resources by manipulating theme settings. This could lead to the exposure of database credentials, API keys, or other private configuration data.

Technologies: flarum/core (Packagist). Vendors: Packagist.

Quick answers

Is CVE-2026-41887 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-41887 being exploited in the wild.
How severe is CVE-2026-41887?
Medium severity, with a CVSS score of 4.9, published 8 May 2026.
Which products and versions are affected?
Flarum <= 1.8.15, >= 2.0.0-beta.1, <= 2.0.0-beta.8; flarum/core (Packagist) ECOSYSTEM:introduced=0,fixed=1.8.16.
Is there a fix for CVE-2026-41887?
Yes. flarum/core (Packagist): upgrade to 1.8.16 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-41887 attacked?
It is attacked over the network, in a web application.
Am I affected by CVE-2026-41887?
Check whether you run Flarum or flarum/core (Packagist) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • flarum/core (Packagist): upgrade to 1.8.16 or later
    composer require flarum/core:^1.8.16

Technical details

An incomplete fix for a previous vulnerability (CVE-2023-27577) failed to restrict @import and data-uri() directives in all LESS configuration variables. While 'custom_less' was protected, other variables like 'theme_primary_color' and 'theme_secondary_color' are interpolated verbatim into the LESS source at compile time. An authenticated administrator can inject an '@import (inline)' directive to include local files (e.g., /etc/passwd, .env) or trigger SSRF requests. The contents of the imported files or external responses are then embedded into the publicly accessible forum.css file. The issue is fixed in versions 1.8.16 and 2.0.0-rc.1.

Affected products

  • Flarum Flarum core <= 1.8.15, >= 2.0.0-beta.1, <= 2.0.0-beta.8

Identifiers

  • CVE-2026-41887
  • GHSA-xjvc-pw2r-6878

Timeline

  • 2026-04-18: advisory: GitHub Security Advisory published
  • 2026-04-18: patched: Version 1.8.16 released
  • 2026-04-20: patched: Version 2.0.0-rc.1 released
  • 2026-05-08: disclosed: CVE-2026-41887 published to NVD

References

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