CVE WatchSep 15, 2026

CVE-2026-12985

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

CVSS

6.8

Medium

EPSS

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KEV

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Exploit Today

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0-100

Published: Sep 14, 2026 · Last modified: Sep 15, 2026 · CWE-601

EPSS · 30d

Not enough EPSS history yet.

Technical description

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

Official references

mattermost.comhttps://mattermost.com/security-updates

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