EUVD-2026-77520
GHSA-c92j-r2f4-67xg
Severity by source
AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N
Network-reachable DCR endpoint requires no auth (PR:N), but crafted URI and victim OAuth interaction impose AC:H and UI:R; account takeover yields C:H/I:H with no availability impact.
Primary rating from Vendor (Mattermost).
CVSS VectorVendor: Mattermost
Lifecycle Timeline
1DescriptionCVE.org
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
AnalysisAI
OAuth redirect URI allowlist bypass in Mattermost's Dynamic Client Registration allows remote unauthenticated attackers to register OAuth clients with attacker-controlled callback hosts. The flaw arises from glob patterns being matched against the raw redirect URI string rather than against parsed URL components, enabling an attacker to embed an allowlisted host or path inside the query string of a malicious URI (e.g., https://evil.com/callback?trusted.example.com/path). …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires that Mattermost's Dynamic Client Registration endpoint is reachable by the attacker - PR:N in the CVSS vector confirms no authentication is needed to register an OAuth client. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The vendor-assigned CVSS 6.8 (AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N) is well-calibrated. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Upgrade Mattermost to a version beyond the affected ranges per the vendor advisory at https://mattermost.com/security-updates - specifically to 11.7.8 or later for 11.7.x deployments, 11.8.5 or later for 11.8.x deployments, or to a patched 11.9.x release for 11.9.0 deployments (exact fix version numbers are not explicitly stated in the input data; verify with the vendor advisory). … Detailed patch versions, workarounds, and compensating controls in full report. |
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