CVE-2024-42406: Unauthorized access on archived channels

Severity: medium (CVSS 5.4 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2024-09-26 · updated 2026-06-17
Weakness: CWE-284

Description

Mattermost versions 9.11.x <= 9.11.0, 9.10.x <= 9.10.1, 9.9.x <= 9.9.2 and 9.5.x <= 9.5.8 fail to properly authorize requests when viewing archived channels is disabled, which allows an attacker to retrieve post and file information about archived channels. Examples are flagged or unread posts as well as files.

Affected products

Mattermost: from 9.5.0 before 9.5.9; from 9.9.0 before 9.9.3; from 9.10.0 before 9.10.2; 9.11.0, 9.11.0-rc1, 9.11.0-rc2, 9.11.0-rc3 — fixed in 9.10.2, 9.5.9, 9.9.3

How to fix

Upgrade to a fixed version: Mattermost 9.10.2, 9.5.9, 9.9.3. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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