Vulnerability DatabaseCVE-2026-5740
Mend.io Vulnerability Database
The largest open source vulnerability database
What is a Vulnerability ID?
New vulnerability? Tell us about it!
CVE-2026-5740
Published:May 22, 2026
Updated:June 11, 2026
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
Affected Packages
https://github.com/mattermost/mattermost.git (GITHUB):
Affected version(s) >=v11.5.0 <v11.5.4
Fix Suggestion:
Update to version v11.5.4
https://github.com/mattermost/mattermost.git (GITHUB):
Affected version(s) >=v10.11.0 <v10.11.15
Fix Suggestion:
Update to version v10.11.15
https://github.com/mattermost/mattermost.git (GITHUB):
Affected version(s) >=v11.4.0 <v11.4.5
Fix Suggestion:
Update to version v11.4.5
https://github.com/mattermost/mattermost.git (GITHUB):
Affected version(s) =v11.6.0 <v11.6.1
Fix Suggestion:
Update to version v11.6.1
github.com/mattermost/mattermost (GO):
Affected version(s) >=v11.4.0 <v11.4.5
Fix Suggestion:
Update to version v11.4.5
github.com/mattermost/mattermost (GO):
Affected version(s) >=v10.11.0 <v10.11.15
Fix Suggestion:
Update to version v10.11.15
github.com/mattermost/mattermost (GO):
Affected version(s) >=v11.5.0 <v11.5.4
Fix Suggestion:
Update to version v11.5.4
github.com/mattermost/mattermost (GO):
Affected version(s) =v11.6.0 <v11.6.1
Fix Suggestion:
Update to version v11.6.1
Related Resources (1)
https://mattermost.com/security-updates
Do you need more information?
Contact Us
CVSS v4
Base Score:
8.7
Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
NONE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
NONE
Vulnerable System Availability
HIGH
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
7.5
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
HIGH
Weakness Type (CWE)
Memory Allocation with Excessive Size Value
CWE-789
EPSS
Base Score:
0.11