CVE-2026-10103

Medium

Description

Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to verify post ownership in the shared channel inbound sync handler, which allows an authenticated remote cluster to modify or delete posts authored by local users or other remotes via crafted sync messages referencing arbitrary post IDs in channels shared with that remote.. Mattermost Advisory ID: MMSA-2026-00689

SeverityMedium

CVSS4.3

Exploit probability—

Product

Mattermost Server

PublishedJul 13, 2026

First seenJul 13, 2026

Weakness typeCWE-639Authorization bypass through user-controlled key

How to fix

Update

mattermost mattermost_server10.11.20, 11.6.5, 11.7.3 or later

Vendor advisories

mattermost.com/security-updates

Affected products

Product	Affected versions	Fixed in
mattermost mattermost_server	10.11.0 ≤ v < 10.11.20, 11.6.0 ≤ v < 11.6.5, 11.7.0 ≤ v < 11.7.3	10.11.20, 11.6.5, 11.7.3

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