CVE-2026-6340
Analyzed Analyzed - Analysis Complete
Memory Exhaustion in Mattermost via Malicious 7zip Archive

Publication date: 2026-05-18

Last updated on: 2026-05-19

Assigner: Mattermost, Inc.

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
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Meta Information
Published
2026-05-18
Last Modified
2026-05-19
Generated
2026-06-10
AI Q&A
2026-05-18
EPSS Evaluated
2026-06-08
NVD
CVE-2026-6340
Affected Vendors & Products
Showing 3 associated CPEs
Vendor Product Version / Range
mattermost mattermost_server From 10.11.0 (inc) to 10.11.14 (exc)
mattermost mattermost_server From 11.4.0 (inc) to 11.4.4 (exc)
mattermost mattermost_server From 11.5.0 (inc) to 11.5.2 (exc)
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Exploitability
CWE
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KEV
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CWE ID Description
CWE-789 The product allocates memory based on an untrusted, large size value, but it does not ensure that the size is within expected limits, allowing arbitrary amounts of memory to be allocated.
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Executive Summary

This vulnerability affects certain versions of Mattermost (11.5.x <= 11.5.1, 10.11.x <= 10.11.13, 11.4.x <= 11.4.3) where the software fails to properly validate the structure of 7zip archives before processing them.

An authenticated attacker can exploit this by uploading a specially crafted 7zip file that contains excessive folder declarations, which causes the server to exhaust its memory resources.

This leads to a denial of service condition on the server.

Impact Analysis

The primary impact of this vulnerability is a denial of service (DoS) on the Mattermost server.

By uploading a malicious 7zip file with excessive folder declarations, an authenticated attacker can cause the server to exhaust its memory, potentially making the service unavailable to legitimate users.

This can disrupt communication and collaboration within an organization relying on Mattermost.

Mitigation Strategies

To mitigate this vulnerability, you should upgrade Mattermost to a version later than the affected versions 11.5.x <= 11.5.1, 10.11.x <= 10.11.13, and 11.4.x <= 11.4.3 where the issue with 7zip archive validation has been fixed.

Additionally, monitor Mattermost's official security updates page and subscribe to their security bulletin for notifications about fixes and patches.

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