CVE-2025-27933: Unauthorized Private-to-Public Channel Conversion

Severity: medium (CVSS 4.3 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: 2025-03-21 · updated 2026-06-17
Weakness: CWE-863

Description

Mattermost versions 10.4.x <= 10.4.2, 10.3.x <= 10.3.3, 9.11.x <= 9.11.8 fail to fail to enforce channel conversion restrictions, which allows members with permission to convert public channels to private ones to also convert private ones to public

Affected products

Mattermost: from 9.11.0 before 9.11.9; from 10.3.0 before 10.3.4; from 10.4.0 before 10.4.3 — fixed in 10.3.4, 10.4.3, 9.11.9

How to fix

Upgrade to a fixed version: Mattermost 10.3.4, 10.4.3, 9.11.9. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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