Medium severity · published May 18, 2026
CVE-2026-6340
Memory Exhaustion via Malicious 7zip File Upload
6.5
CVSS
0.2%
EPSS
No
On KEV
Description
Mattermost versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3 fail to validate 7zip archive structure before processing which allows an authenticated attacker to cause server memory exhaustion and denial of service via uploading a specially crafted 7zip file with excessive folder declarations.. Mattermost Advisory ID: MMSA-2026-00573
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.2% · higher than 15% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
MA
Mattermost · Mattermost
11.5.0 through 11.5.1; 10.11.0 through 10.11.13; 11.4.0 through 11.4.3 · source: vendor
MS
Mattermost Server · Mattermost
10.11.0 before 10.11.14; 11.4.0 before 11.4.4; 11.5.0 before 11.5.2 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-6340
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-6340
Vendor Advisory
https://mattermost.com/security-updates
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