# CVE-2026-12985

## Summary

- **CVE ID:** CVE-2026-12985
- **Severity:** MEDIUM
- **CVSS Score:** 6.8 (CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N)
- **CWE:** CWE-601
- **Published:** Sep 14, 2026
- **Last Modified:** Sep 15, 2026

## 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

## Affected Products

- Mattermost — Mattermost (11.9.0)
- Mattermost — Mattermost (11.8.0)
- Mattermost — Mattermost (11.7.0)
- Mattermost — Mattermost (11.10.0)
- Mattermost — Mattermost (11.9.1)
- Mattermost — Mattermost (11.8.5)
- Mattermost — Mattermost (11.7.8)

## References

- [CNA](https://mattermost.com/security-updates)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.28%
- **EPSS Percentile:** 20.5

---
_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-17._