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CVE-2026-10556

Unauthenticated webhook request with null notification entry could crash the Microsoft Calendar plugin.

CVSS 3.1 5.3 MEDIUMCheck source for fixed versionsKEV status unknown
Original advisory

cve-program · CVE-2026-10556

Published

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

Read the publisher's advisory

Affected versions, risk and source history

Related advisories and sources

Publishers link these advisories through the identifiers shown below. A shared identifier or date alone does not tell you whether your software is affected or whether the advisories describe the same cause.

CVE-2026-10556 · CVE overview and exploitation status

cve-program · CVE-2026-10556

Related changes

Linked by CVE identifier

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