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CVE PROGRAM SOURCE RECORD5.3 Medium

CVE-2026-10556

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

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Status
Published
Published
Updated
Assigning organization
Mattermost

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

Affected products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

Mattermost Mattermost

Default version status: unaffected

  • 11.9.0 to ≤ 11.9.0affected
  • 11.8.0 to ≤ 11.8.4affected
  • 11.7.0 to ≤ 11.7.7affected
  • 10.11.0 to ≤ 10.11.22affected
  • 11.10.0unaffected
  • 11.9.1unaffected
  • 11.8.5unaffected
  • 11.7.8unaffected
  • 10.11.23unaffected

References