CVE-2026-10556

MediumCVSS 5.3/10Last modified Oct 7, 2026

Description

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

Metrics

CVSS 3.1 5.3/10CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Weakness enumeration

CWE-754 CWE-476

Affected software

No affected versions have been published.

Timeline

Published: Sep 14, 2026
Last modified: Oct 7, 2026
NVD status: Analyzed

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