CVE-2026-5740
Unauthenticated WebSocket binary frame causes denial of service in Mattermost Server
Published: May 22, 2026Updated: May 22, 2026 Sources: CVE List BDUCWE-789CWE-789: Memory Allocation with Excessive Size Value
7.5CVSSHIGH
Description
Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to properly validate msgpack-encoded WebSocket frames before memory allocation which allows an unauthenticated remote attacker to crash the server process and cause a full service outage for all users via a crafted binary WebSocket message sent to the public WebSocket endpoint.. Mattermost Advisory ID: MMSA-2026-00647
CVSS Vector Breakdown
Exploitability
AV:NAttack VectorNetwork
AC:LAttack ComplexityLow
PR:NPrivileges RequiredNone
UI:NUser InteractionNone
Scope
S:UScopeUnchanged
Impact
C:NConfidentialityNone
I:NIntegrityNone
A:HAvailabilityHigh
Weaknesses
Affected Products
Exploitability
Official Patch Available
References
Timeline
Published
May 22, 2026
Last Updated
May 22, 2026
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