GHSA-xjvc-pw2r-6878: flarum/core (CVE-2026-41887)

Package	Ecosystem	Affected	Fixed in
flarum/core	Packagist	<1.8.16 \|\| >=2.0.0-beta.1, <2.0.0-rc.1	1.8.16, 2.0.0-rc.1

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Flarum (flarum/core) versions before 1.8.16, and 2.0.0-beta.1 up to but not including 2.0.0-rc.1, are affected. An attacker with administrator access can enter a theme color value that injects an import directive into the compiled stylesheet, letting them read local files on the server or make outbound requests from it. Upgrade to flarum/core 1.8.16 or 2.0.0-rc.1. No configuration workaround is listed beyond protecting administrator accounts.

Written 3 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

Score	Rating	CVSS	Vector	Source
4.9	Medium	3.1	CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:N/A:N	CNA (GitHub_M)

CISA KEV Not listed.
EPSS 0.0047, the 41st percentile, on 14 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

31 Oct 2026, 14:25 UTC First seen by agentprime
31 Oct 2026, 14:25 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.