PT-2026-41655 · Mattermost · Mattermost

Daw10 · Published 2026-05-18 · Updated 2026-05-18 · CVE-2026-5163

Positive Technologies (AI Summary)

CVSS v3.1

6.5

Medium

Base vector

AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

Name of the Vulnerable Software and Affected Versions Mattermost versions 11.5.x through 11.5.1

Description An issue exists where channel membership is not verified during the processing of AI-assisted message rewrites. This allows an authenticated attacker to read the content of threads in private channels and direct messages they are not authorized to access by sending a crafted request to the 'post rewrite' endpoint.

Recommendations Update Mattermost to a version later than 11.5.1.

Fix

Missing Authorization

Weakness Enumeration

CWE-862

Related Identifiers

CVE-2026-5163

GHSA-8R89-8W26-CQ32

Affected Products

Mattermost

References · 8

• https://nvd.nist.gov/vuln/detail/CVE-2026-5163 · Security Note
• https://osv.dev/vulnerability/GHSA-8r89-8w26-cq32 · Vendor Advisory
• https://mattermost.com/security-updates · Vendor Advisory
• https://github.com/mattermost/mattermost/commit/f4d1abe7e8f545f1a87f463fa9fe451c731aebf8 · Note
• https://github.com/mattermost/mattermost · Note
• https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-5163 · Note
• https://twitter.com/CVEarity/status/2056409542192484676 · Twitter Post
• https://t.me/CVEtracker/54115 · Telegram Post