Mattermost up to 11.7.7/11.8.4/11.9.0 Dynamic Client Registration redirect

Summaryinfo

A vulnerability marked as problematic has been reported in Mattermost up to 11.7.7/11.8.4/11.9.0. This issue affects some unknown processing of the component Dynamic Client Registration. This manipulation causes redirect. This vulnerability is handled as CVE-2026-12985. The attack can be initiated remotely. There is not any exploit available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability classified as problematic was found in Mattermost up to 11.7.7/11.8.4/11.9.0. Affected by this vulnerability is an unknown code of the component Dynamic Client Registration. The manipulation with an unknown input leads to a redirect vulnerability. The CWE definition for the vulnerability is CWE-601. A web application accepts a user-controlled input that specifies a link to an external site, and uses that link in a Redirect. This simplifies phishing attacks. As an impact it is known to affect integrity. The summary by CVE is:

Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7 Mattermost failed to validate Dynamic Client Registration redirect URIs by URL component (matching glob patterns against the raw URI string instead) which allows a remote unauthenticated attacker to register an OAuth client with an attacker-controlled callback host that bypasses the configured redirect URI allowlist via a crafted redirect URI that places an allowlisted host/path suffix inside the query string.. Mattermost Advisory ID: MMSA-2026-00700

The advisory is shared at mattermost.com. This vulnerability is known as CVE-2026-12985 since 06/23/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. It demands that the victim is doing some kind of user interaction. Neither technical details nor an exploit are publicly available. MITRE ATT&CK project uses the attack technique T1204.001 for this issue.

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

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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
• 11.8
• 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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Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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