Improper Access Control in Mattermost Products
CVE-2026-4274

5.4MEDIUM

Key Information:

Vendor

Mattermost
Status
Mattermost
Vendor
CVE Published:
26 March 2026

What is CVE-2026-4274?

Certain versions of Mattermost contain a vulnerability that fails to restrict team-level access when processing membership synchronization from remote clusters. This oversight permits malicious actors within those remote clusters to manipulate team memberships, potentially granting unauthorized access to private teams instead of merely shared channels. The issues lie within the handling of crafted membership sync messages that could trigger inappropriate team membership assignments.

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Affected Version(s)

Mattermost 11.2.0 <= 11.2.2

Mattermost 10.11.0 <= 10.11.10

Mattermost 11.4.0

References

https://mattermost.com/security-updates
vendor-advisory

CVSS V3.1

Score:
5.4
Severity:
MEDIUM
Confidentiality:
Low
Integrity:
Low
Availability:
Low
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
Low
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

daw10
JSON
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