CVE-2025-6226: IDOR in CreatePost API allows for timeboxed message disclosure

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-07-18 · updated 2026-06-17
Weakness: CWE-306

Description

Mattermost versions 10.5.x <= 10.5.6, 10.8.x <= 10.8.1, 10.7.x <= 10.7.3, 9.11.x <= 9.11.16 fail to verify authorization when retrieving cached posts by PendingPostID which allows an authenticated user to read posts in private channels they don't have access to via guessing the PendingPostID of recently created posts.

Affected products

Mattermost: from 9.11.0 before 9.11.17; from 10.5.0 before 10.5.7; from 10.7.0 before 10.7.4; from 10.8.0 before 10.8.2 — fixed in 10.5.7, 10.7.4, 10.8.2, 9.11.17

How to fix

Upgrade to a fixed version: Mattermost 10.5.7, 10.7.4, 10.8.2, 9.11.17. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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