CVE-2026-10556CWE-476CWE-754

CVE-2026-10556

Medium · published September 14, 2026

CVSS v3.1
5.3
EPSS
0%
Percentile
15.2
In the wild
Unconfirmed
What it is

Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22 fail to validate null entries in Microsoft Graph webhook notification payloads, which allows an unauthenticated attacker to crash the Microsoft Calendar plugin process and deny calendar integration service to all users on the instance via a crafted {{POST}} request to the public webhook endpoint.. Mattermost Advisory ID: MMSA-2026-00693

The record
Technical detail
CVSS v3.1
5.3 · MEDIUM
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
CVSS v4.0
Not supplied
EPSS
0.00248 · 15.2th percentile
Weaknesses
CWE-476 · NULL Pointer Dereference; CWE-754 · Improper Check for Unusual or Exceptional Conditions
Published
2026-09-14T15:17Z
Affected products (4)
ProductVersionsFixed in
mattermost/mattermost_server≥ 10.11.0, < 10.11.2310.11.23
mattermost/mattermost_server≥ 11.7.0, < 11.7.811.7.8
mattermost/mattermost_server≥ 11.8.0, < 11.8.511.8.5
mattermost/mattermost_server≥ 11.9.0, < 11.9.111.9.1
References (1)
https://mattermost.com/security-updates · [email protected]
EPSS history
Timeline
  • 16 SEP 04:24Z
    EPSS moved — → 0%
    epss
  • 14 SEP 10:46Z
    Unauthenticated webhook request with null notification entry could crash the Microsoft Calendar plugin.
    cvelistv5