CVE-2026-10103 PUBLISHED

Authenticated remote cluster can modify or delete posts it does not own in Mattermost Connected Workspaces shared channels

Assigner: Mattermost
Reserved: 29.05.2026 Published: 13.07.2026 Updated: 13.07.2026

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

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N
CVSS Score: 4.3

Attack Vector	Network	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	None
Privileges Required	Low	Integrity Impact	Low
User Interaction	None	Availability Impact	None

CVSS 3.1

Product Status

Vendor	Mattermost
Product	Mattermost
Versions	Default: unaffected affected from 11.7.0 to 11.7.2 (incl.) affected from 11.6.0 to 11.6.4 (incl.) affected from 10.11.0 to 10.11.19 (incl.) Version 11.8.0 is unaffected Version 11.7.3 is unaffected Version 11.6.5 is unaffected Version 10.11.20 is unaffected

Solutions

Update Mattermost to versions 11.8.0, 11.7.3, 11.6.5, 10.11.20 or higher.

Credits

ratrarity finder

References

MMSA-2026-00689

Problem Types

CWE-639: Authorization Bypass Through User-Controlled Key CWE