CVE-2026-5740
Unauthenticated WebSocket binary frame causes denial of service in Mattermost Server
CVSS Score
7.5
EPSS Score
0.0%
EPSS Percentile
0th
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
| CWE | CWE-789 |
| Vendor | mattermost |
| Product | mattermost |
| Published | May 22, 2026 |
| Last Updated | May 22, 2026 |
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CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High
Affected Versions
Mattermost / Mattermost
11.6.0 ≤ 11.6.0 11.5.0 ≤ 11.5.3 11.4.0 ≤ 11.4.4 10.11.0 ≤ 10.11.14
Credits
ZephrFish