Vulnerability · Published Jul 13, 2026 · Assigned by Mattermost

CVE-2026-9708Incoming webhook user attribution via unvalidated webhook owner

Medium 4.9

In plain English

A medium-severity authorization bypass via user-controlled key in Mattermost from Mattermost. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 30% of all known vulnerabilities).

Severity (CVSS 3.1)4.9Medium

Exploit odds (30 days)0.4%top 70.0% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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

Affected products (as reported)

Vendor	Product	Versions
Mattermost	Mattermost	11.7.0 – through 11.7.211.6.0 – through 11.6.410.11.0 – through 10.11.19

Weakness: CWE-639 · Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N

References

MMSA-2026-00683 vendor-advisory