CVE-2026-9708

Incoming webhook user attribution via unvalidated webhook owner

State: Published
Severity: 4.9 Medium
Published: Jul 13, 2026
Updated: Jul 13, 2026
Reserved: May 27, 2026

Description

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

Scores

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

Weaknesses

CWE-639 Authorization Bypass Through User-Controlled Key

Affected Products

Product	Versions
MattermostMattermost	11.7.0 through 11.7.2Affected 11.6.0 through 11.6.4Affected 10.11.0 through 10.11.19Affected 11.8.0Not affected 11.7.3Not affected 11.6.5Not affected 10.11.20Not affected

References

MMSA-2026-00683vendor-advisory

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