Mattermost up to 11.7.9/11.8.5/11.9.1/11.10.0 input validation

Summaryinfo

A vulnerability labeled as critical has been found in Mattermost up to 11.7.9/11.8.5/11.9.1/11.10.0. Affected is an unknown function. The manipulation results in input validation. This vulnerability is known as CVE-2026-18223. It is possible to launch the attack remotely. No exploit is available. The affected component should be upgraded.

Detailsinfo

A vulnerability classified as critical has been found in Mattermost up to 11.7.9/11.8.5/11.9.1/11.10.0. Affected is an unknown part. The manipulation with an unknown input leads to a input validation vulnerability. CWE is classifying the issue as 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. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

Mattermost versions 11.10.x <= 11.10.0, 11.7.x <= 11.7.9, 11.9.x <= 11.9.1, 11.8.x <= 11.8.5 fail to validate the invited recipient's email address when redeeming team and guest invitation tokens, which allows an authenticated attacker to join a team or gain unauthorized access to private channels via a forwarded or leaked invitation link.. Mattermost Advisory ID: MMSA-2026-00747

The advisory is shared for download at mattermost.com. This vulnerability is traded as CVE-2026-18223 since 07/29/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. Successful exploitation requires user interaction by the victim. There are neither technical details nor an exploit publicly available.

Upgrading to version 11.7.10, 11.8.6, 11.9.2, 11.10.1 or 11.11.0 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-102748). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Type

• Groupware Software

Name

• Mattermost

Version

• 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
• 11.7.8
• 11.7.9
• 11.8
• 11.8.0
• 11.8.1
• 11.8.2
• 11.8.3
• 11.8.4
• 11.8.5
• 11.9
• 11.9.0
• 11.9.1
• 11.10.0

License

• open-source

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VulDB is the best source for vulnerability data and more expert information about this specific topic.

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