CVE-2025-20051: Arbitrary file read via block duplication in Mattermost Boards

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.6% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-02-24 · updated 2026-06-17
Weakness: CWE-22

Description

Mattermost versions 10.4.x <= 10.4.1, 9.11.x <= 9.11.7, 10.3.x <= 10.3.2, 10.2.x <= 10.2.2 fail to properly validate input when patching and duplicating a board, which allows a user to read any arbitrary file on the system via duplicating a specially crafted block in Boards.

Affected products

Mattermost: from 9.11.0 before 9.11.8; from 10.2.0 before 10.2.3; from 10.3.0 before 10.3.3; from 10.4.0 before 10.4.2 — fixed in 10.2.3, 10.3.3, 10.4.2, 9.11.8

How to fix

Upgrade to a fixed version: Mattermost 10.2.3, 10.3.3, 10.4.2, 9.11.8. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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