# CVE-2026-12985: Mattermost DCR redirect URI allowlist bypass via improper URL component validation

> CVE-2026-12985: Mattermost DCR redirect URI allowlist bypass via improper URL component validation. CVSS 6.8 (CVSS 3.1).

Canonical: https://rewindex.com/cve/CVE-2026-12985
Last updated: 2026-10-07T17:58:56Z

- Published: 2026-09-14 14:09 UTC · Updated: 2026-10-07 17:58 UTC · Assigner: Mattermost
- CVSS: 6.8 (CVSS 3.1) · Severity: Medium · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N
- EPSS: 0.27%, 19th percentile (scored 2026-10-25)
- CISA KEV: no
- CWE: CWE-601

## 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 vendors and products

- Mattermost: Mattermost

## Tracked companies

- [Mattermost](https://rewindex.com/company/mattermost.md)

## References

- [CVE record on cve.org](https://www.cve.org/CVERecord?id=CVE-2026-12985)
- [NVD entry](https://nvd.nist.gov/vuln/detail/CVE-2026-12985)
- [https://mattermost.com/security-updates](https://mattermost.com/security-updates)

---

_Sources: CVE records from the CVE Program (cve.org). CVE® is a registered trademark of The MITRE Corporation. (https://www.cve.org/) This product uses data from the NVD API but is not endorsed or certified by the NVD. (https://nvd.nist.gov/) Known Exploited Vulnerabilities catalog from CISA. (https://www.cisa.gov/known-exploited-vulnerabilities-catalog) EPSS scores from FIRST (Exploit Prediction Scoring System). (https://www.first.org/epss/)_


---
Canonical: https://rewindex.com/cve/CVE-2026-12985 · Markdown: https://rewindex.com/cve/CVE-2026-12985.md · JSON: https://rewindex.com/api/v1/cves/CVE-2026-12985 · Data licensed CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/) · Generated 2026-10-26T03:09:22.234Z