PT-2026-28642 · Mattermost · Mattermost

Daw10 · Published 2026-03-26 · Updated 2026-03-26 · CVE-2026-4274

Positive Technologies (AI Summary)

CVSS v3.1

5.4

Medium

Base vector

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

Name of the Vulnerable Software and Affected Versions Mattermost versions 10.11.0 through 10.11.10 Mattermost versions 11.2.0 through 11.2.2 Mattermost versions 11.3.0 through 11.3.1 Mattermost versions 11.4.0

Description The software does not properly restrict team-level access when processing membership synchronization from a remote cluster. This allows a malicious remote cluster to grant a user access to an entire private team instead of only the shared channel. This is achieved by sending crafted membership synchronization messages that trigger team membership assignment.

Recommendations Update Mattermost to a version later than 10.11.10. Update Mattermost to a version later than 11.2.2. Update Mattermost to a version later than 11.3.1. Update Mattermost to a version later than 11.4.0.

Fix

Incorrect Authorization

Weakness Enumeration

CWE-863

Related Identifiers

CVE-2026-4274

GHSA-G7FP-CQJ5-X8HF

Affected Products

Mattermost

References · 6

• https://mattermost.com/security-updates · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2026-4274 · Security Note
• https://osv.dev/vulnerability/GHSA-g7fp-cqj5-x8hf · Vendor Advisory
• https://github.com/mattermost/mattermost · Note
• https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2026-4274 · Note
• https://twitter.com/CVEnew/status/2037137711186764276 · Twitter Post