CVE-2025-27571: Channel metadata visible in archived channels despite configuration setting

Severity: medium (CVSS 4.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-04-16 · updated 2026-06-17
Weakness: CWE-863

Description

Mattermost versions 10.5.x <= 10.5.1, 10.4.x <= 10.4.3, 9.11.x <= 9.11.9 fail to check the "Allow Users to View Archived Channels" configuration when fetching channel metadata of a post from archived channels, which allows authenticated users to access such information when a channel is archived.

Affected products

Mattermost: from 9.11.0 before 9.11.10; from 10.4.0 before 10.4.4; from 10.5.0 before 10.5.2 — fixed in 10.4.4, 10.5.2, 9.11.10

How to fix

Upgrade to a fixed version: Mattermost 10.4.4, 10.5.2, 9.11.10. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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