Mattermost up to 10.11.22/11.7.7/11.8.4/11.9.0 Calendar Plugin input validation

Summaryinfo

A vulnerability, which was classified as problematic, was found in Mattermost up to 10.11.22/11.7.7/11.8.4/11.9.0. This affects an unknown function of the component Calendar Plugin. Executing a manipulation can lead to input validation. This vulnerability is registered as CVE-2026-10556. It is possible to launch the attack remotely. No exploit is available. You should upgrade the affected component.

Detailsinfo

A vulnerability has been found in Mattermost up to 10.11.22/11.7.7/11.8.4/11.9.0 and classified as problematic. This vulnerability affects some unknown functionality of the component Calendar Plugin. The manipulation with an unknown input leads to a input validation vulnerability. The CWE definition for the vulnerability is CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. As an impact it is known to affect availability. CVE summarizes:

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

The advisory is available at mattermost.com. This vulnerability was named CVE-2026-10556 since 06/01/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. The technical details are unknown and an exploit is not available.

Upgrading to version 10.11.23, 11.7.8, 11.8.5, 11.9.1 or 11.10.0 eliminates this vulnerability.

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Productinfo

Type

• Groupware Software

Name

• Mattermost

Version

• 10.11.0
• 10.11.1
• 10.11.2
• 10.11.3
• 10.11.4
• 10.11.5
• 10.11.6
• 10.11.7
• 10.11.8
• 10.11.9
• 10.11.10
• 10.11.11
• 10.11.12
• 10.11.13
• 10.11.14
• 10.11.15
• 10.11.16
• 10.11.17
• 10.11.18
• 10.11.19
• 10.11.20
• 10.11.21
• 10.11.22
• 11.0
• 11.1
• 11.2
• 11.3
• 11.4
• 11.5
• 11.6
• 11.7
• 11.7.0
• 11.7.1
• 11.7.2
• 11.7.3
• 11.7.4
• 11.7.5
• 11.7.6
• 11.7.7
• 11.8
• 11.8.0
• 11.8.1
• 11.8.2
• 11.8.3
• 11.8.4
• 11.9.0

License

• open-source

CPE 2.3info

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CPE 2.2info

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