CVE-2026-12985: mattermost server from 11.7.0 (inclusive), before 11.7.8 (exclusive), from 11.8.0 (inclusive), before 11.8.5…

Affected technology

mattermost server · from 11.7.0 (inclusive), before 11.7.8 (exclusive)
mattermost

mattermost server · from 11.8.0 (inclusive), before 11.8.5 (exclusive)
mattermost

mattermost server · from 11.9.0 (inclusive), before 11.9.1 (exclusive)
mattermost

Mattermost · 11.9.0 through 11.9.0, 11.8.0 through 11.8.4, 11.7.0 through 11.7.7
Mattermost

Description’s affected range: versions 11.9.x <= 11.9.0

Component: Not specified by the source

Attack conditions (Vendor/CNA, CVSS 3.1): Network (remote) · No privileges required · User interaction required

Attack conditions (NVD, CVSS 3.1): Network (remote) · No privileges required · User interaction required

What an attacker can do

A remote unauthenticated attacker can 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. Vendor/CNA’s CVSS 3.1 assessment (base score 6.8/10) rates confidentiality and integrity impact as high; availability impact as none. NVD’s CVSS 3.1 assessment (base score 9.3/10) rates confidentiality and integrity impact as high; availability impact as none.