Unauthenticated WebSocket binary frame causes denial of service in Mattermost Server
Summary
| CVE | CVE-2026-5740 |
|---|---|
| State | PUBLISHED |
| Assigner | Mattermost |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-05-22 11:16:23 UTC |
| Updated | 2026-07-23 16:10:00 UTC |
| 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 |
Risk And Classification
Primary CVSS: v3.1 7.5 HIGH from [email protected]
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Problem Types: CWE-789 | CWE-789 CWE-789: Memory Allocation with Excessive Size Value
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | [email protected] | Secondary | 7.5 | HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
| 3.1 | CNA | CVSS | 7.5 | HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
LowPrivileges Required
NoneUser Interaction
NoneScope
UnchangedConfidentiality
NoneIntegrity
NoneAvailability
HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD Known Affected Configurations (CPE 2.3)
| Type | Vendor | Product | Version | Update | Edition | Language |
|---|---|---|---|---|---|---|
| Application | Mattermost | Mattermost Server | All | All | All | All |
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Mattermost | Mattermost | affected 11.6.0 11.6.0 semver | Not specified |
| CNA | Mattermost | Mattermost | affected 11.5.0 11.5.3 semver | Not specified |
| CNA | Mattermost | Mattermost | affected 11.4.0 11.4.4 semver | Not specified |
| CNA | Mattermost | Mattermost | affected 10.11.0 10.11.14 semver | Not specified |
| CNA | Mattermost | Mattermost | unaffected 11.7.0 | Not specified |
| CNA | Mattermost | Mattermost | unaffected 11.6.1 | Not specified |
| CNA | Mattermost | Mattermost | unaffected 11.5.4 | Not specified |
| CNA | Mattermost | Mattermost | unaffected 11.4.5 | Not specified |
| CNA | Mattermost | Mattermost | unaffected 10.11.15 | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| mattermost.com/security-updates | [email protected] | mattermost.com | Vendor Advisory |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: ZephrFish (en)
Additional Advisory Data
Solutions
CNA: Update Mattermost to versions 11.7.0, 11.6.1, 11.5.4, 11.4.5, 10.11.15 or higher.
There are currently no legacy QID mappings associated with this CVE.