CVE-2026-12985

critical

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 compone…

Vendor / product: Mattermost — mattermost server

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

CVSS

9.3

9.3 (CVSS v3.1)

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N

Severity source: NVD CVSS v3.1 (nvd@nist.gov)

Timeline (UTC)

Published: 2026-09-14 15:17

Modified: 2026-10-07 17:58

NVD status: Analyzed

Last synced 1 day ago

Verified against the source API 2026-10-27 07:07 UTC

Exploitation

Not listed in CISA KEV (as of last catalog sync)

Absence from KEV does not mean a CVE is not exploited. Exploitation status: unknown (no authoritative evidence in our sources).

Affected products

mattermost / mattermost_server ≥11.7.0 <11.7.8, ≥11.8.0 <11.8.5, ≥11.9.0 <11.9.1

Weakness classification (CWE)

CWE-601

Source: NVD / CISA. “NVD-CWE-Other” and “NVD-CWE-noinfo” mean NVD could not assign a specific weakness.

Mitigation & advisories

Vendor advisory: https://mattermost.com/security-updates

References

https://mattermost.com/security-updates responsibledisclosure@mattermost.com

Data sources

NVD CVE API 2.0 — fetched 2026-10-27 07:07 UTC · record ↗

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CVE-2026-12985

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