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CVE-2026-5740

⚠️ high
🔍 Scan for this CVE
Summary

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 Score
7.5
High
EPSS Score
0.1
Exploit Probability
Published Date
2026-05-22
First Seen: 2026-05-27
📊 Relative Risk Intelligence

This CVE is Moderate Risk - more severe than 69.0% of all 326,604 vulnerabilities in our database.

#101,315
Above average severity
Severity Percentile
🎯 CISA SSVC Assessment Updated: May 22, 2026
🔍 Exploitation Status
None
No known exploits
⚙️ Automatable
YES
Can be exploited automatically
💥 Technical Impact
Partial
Limited system impact
🏆 Discovered By
ZephrFish
SSVC data provided by CISA
Last Modified 2026-05-22
Source NVD 🔗
CVSS Vector 3.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE IDs (Weakness Types)
CWE-789

📦 Affected Products 4

Vendor Product Status Affected Versions
mattermost mattermost_server Affected
> 10.11.0 < 10.11.15
mattermost mattermost_server Affected
> 11.4.0 < 11.4.5
mattermost mattermost_server Affected
> 11.5.0 < 11.5.4
mattermost mattermost_server Affected
> 11.6.0 < 11.6.1

🔗 References 1

https://mattermost.com/security-updates
Vendor Advisory

🔗 Related CVEs 6

CVE ID Severity CVSS EPSS Summary Published
CVE-2026-4915 🔶 medium 6.5 0.1 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 filter nil element... 2026-05-25
CVE-2026-3473 🔶 medium 5.9 0.0 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 validate file owne... 2026-05-22
CVE-2026-3636 🔶 medium 4.3 0.0 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 sanitize team memb... 2026-05-22
CVE-2026-4635 🔶 medium 6.5 0.0 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 archive the channe... 2026-05-22
CVE-2026-4646 🔶 medium 4.3 0.1 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 validate user-supp... 2026-05-22
CVE-2026-5308 🔶 medium 4.9 0.1 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 enforce request bo... 2026-05-22
These CVEs affect the same products