CVE-2026-9708 PUBLISHED

Incoming webhook user attribution via unvalidated webhook owner

Assigner: Mattermost
Reserved: 27.05.2026 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 validate that an assigned incoming webhook user has access to the target team or channel, which allows a requester with webhook management permissions to create posts or direct messages attributed to another user via crafted incoming webhook configuration and payloads.. Mattermost Advisory ID: MMSA-2026-00683

Metrics

CVSS 3.1

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N
CVSS Score: 4.9

Attack Vector	Network	Scope	Unchanged
Attack Complexity	Low	Confidentiality Impact	None
Privileges Required	High	Integrity Impact	High
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

arang finder

References

MMSA-2026-00683

Problem Types

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