CVE-2026-5163: mattermost server from 11.5.0 (inclusive), before 11.5.2 (exclusive); +1 more affected products

Affected technology

mattermost server · from 11.5.0 (inclusive), before 11.5.2 (exclusive)
mattermost

Mattermost · 11.5.0 through 11.5.1
Mattermost

Description’s affected range: versions 11.5.x <= 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which

Component: Not specified by the source

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

What an attacker can do

The source says mattermost versions 11.5.x <= 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an authenticated attacker to read the content of threads in private channels and direct messages they do not have access to via a crafted request to the post rewrite endpoint. Vendor/CNA’s CVSS 3.1 assessment (base score 6.5/10) rates confidentiality impact as high; integrity and availability impact as none.