CVE-2026-10556

published 2026-09-14

CVE-2026-10556: 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…

Priority P4 32 medium 5.3 CVSS 3.1

AV N AC L PR N UI N S U C N I N A L

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

Affected

8 ranges

Vendor	Product	Version range	Fixed in
mattermost	mattermost	10.11.0 – 10.11.22	—
mattermost	mattermost	11.7.0 – 11.7.7	—
mattermost	mattermost	11.8.0 – 11.8.4	—
mattermost	mattermost	11.9.0 – 11.9.0	—
mattermost	mattermost_server	>= 10.11.0 < 10.11.23	10.11.23
mattermost	mattermost_server	>= 11.7.0 < 11.7.8	11.7.8
mattermost	mattermost_server	>= 11.8.0 < 11.8.5	11.8.5
mattermost	mattermost_server	>= 11.9.0 < 11.9.1	11.9.1

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CWE-754