CVE-2026-9708CWE-639

Incoming webhook user attribution via unvalidated webhook owner

Medium · published July 13, 2026

CVSS v3.1
4.9
EPSS
0%
Percentile
28.6
In the wild
Unconfirmed
What it is

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

The record
Technical detail
CVSS v3.1
4.9 · MEDIUM
Vector
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:N
CVSS v4.0
Not supplied
EPSS
0.00361 · 28.6th percentile
Weakness
CWE-639 · Authorization Bypass Through User-Controlled Key
Published
2026-07-13T08:00Z
EPSS history
Timeline
  • 13 JUL 08:00Z
    Incoming webhook user attribution via unvalidated webhook owner
    cvelistv5