GitHub Advisoryadvisory · Go

GHSA-8r89-8w26-cq32 Mattermost doesn't verify channel membership when processing AI-assisted message rewrites

MEDIUM Published 2026-05-18 Modified 2026-06-01 Official page ↗
Aliases
CVE-2026-5163
Ecosystem
Go
Packages
github.com/mattermost/mattermost/server/v8, github.com/mattermost/mattermost-server
Severity
Moderate
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Weaknesses
CWE-862
Reviewed
2026-06-01

Affected packages

• Go github.com/mattermost/mattermost/server/v8: >= 11.5.0, < 11.5.2 → fixed in 11.5.2 • Go github.com/mattermost/mattermost/server/v8: < 8.0.0-20260401090745-f4d1abe7e8f5 → fixed in 8.0.0-20260401090745-f4d1abe7e8f5 • Go github.com/mattermost/mattermost-server: < 5.3.2-0.20260401090745-f4d1abe7e8f5 → fixed in 5.3.2-0.20260401090745-f4d1abe7e8f5

Description

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.. Mattermost Advisory ID: MMSA-2026-00645

Related

Alias · CVE (1)

  • CVE-2026-5163 Mattermost versions 11.5.x <= 11.5.1 fail to verify channel membership when processing AI-assisted message rewrites which allows an… vulnerability

Weakness · CWE (1)

  • CWE-862 Missing Authorization weakness

References