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CVE-2026-10556 (GCVE-0-2026-10556)

Vulnerability from cvelistv5 – Published: 2026-09-14 10:46 – Updated: 2026-09-14 11:19
VLAI
Title
Unauthenticated webhook request with null notification entry could crash the Microsoft Calendar plugin.
Summary
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
Severity
5.3 (Medium)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
SSVC
Exploitation: none Automatable: yes Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-14 11:04 UTC
CWE
  • CWE-754 - Improper Check for Unusual or Exceptional Conditions
Assigner
References
URL Tags
https://mattermost.com/security-updates vendor-advisory
Impacted products
Vendor Product Version CPE status
Mattermost Mattermost Affected: 11.9.0 , ≤ 11.9.0 (semver)
Affected: 11.8.0 , ≤ 11.8.4 (semver)
Affected: 11.7.0 , ≤ 11.7.7 (semver)
Affected: 10.11.0 , ≤ 10.11.22 (semver)
Unaffected: 11.10.0
Unaffected: 11.9.1
Unaffected: 11.8.5
Unaffected: 11.7.8
Unaffected: 10.11.23
guessed Create a notification for this product.
Credits
kamil-sawicki
Show details on NVD website
To clipboard 

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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.


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Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.