CVE-2026-12985: Open Redirect (CVSS 6.8)

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

Is your site exposed to CVE-2026-12985?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

6.8

MEDIUM

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

EPSS — Exploit Prediction

0.0028

Probability of exploitation

0.21%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-601 CWE-601

References

Other References

https://mattermost.com/security-updates

Frequently Asked Questions

What is 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 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 It has a CVSS v3.1 base score of 6.8 (MEDIUM).

How severe is CVE-2026-12985? +

CVE-2026-12985 has a CVSS v3.1 score of 6.8 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0028, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-12985? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2024-53995

SickChill is an automatic video library manager for TV shows. A user-controlled `login` endpoint's `next_` parameter takes arbitrary content. Prior …

CVE-2026-40299

next-intl provides internationalization for Next.js. Applications using the `next-intl` middleware prior to version 4.9.1with `localePrefix: 'as-needed'` could construct URLs where …

CVE-2026-42350

Kargo manages and automates the promotion of software artifacts. Prior to versions 1.7.10, 1.8.13, 1.9.8, and 1.10.2, Kargo is vulnerable …

CVE-2026-8152

Unblu Spark contains an open redirect vulnerability that can be escalated to a DOM-based cross-site scripting (XSS) attack. When Unblu …

CVE-2026-10839

Open redirection vulnerability in the authentication system allows an attacker to use manipulated values in the X-Forwarded-Host header to alter …

CVE-2026-10837

Open redirection vulnerability due to insufficient validation of the X-Forwarded-Host HTTP header. An attacker could create manipulated links that, when …

CVE-2026-12985