Server Memory Exhaustion Vulnerability in Mattermost Product
CVE-2026-6340

4.3MEDIUM

Key Information:

Vendor

Mattermost
Status
Mattermost
Vendor
CVE Published:
18 May 2026

What is CVE-2026-6340?

Mattermost versions 11.5.x up to 11.5.1, 10.11.x up to 10.11.13, and 11.4.x up to 11.4.3 are susceptible to a vulnerability that fails to validate the structure of 7zip archives before processing them. This flaw allows authenticated users to upload a specially crafted 7zip file featuring excessive folder declarations, triggering server memory exhaustion and resulting in denial of service. The vulnerability poses risks to server performance and availability, making it essential for users to update to secure versions.

Affected Version(s)

Mattermost 11.5.0 <= 11.5.1

Mattermost 10.11.0 <= 10.11.13

Mattermost 11.4.0 <= 11.4.3

References

https://mattermost.com/security-updates
vendor-advisory

CVSS V3.1

Score:
4.3
Severity:
MEDIUM
Confidentiality:
None
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
Low
User Interaction:
None
Scope:
Unchanged

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Juho Forsén
.