CVE-2026-14298: Boards archive import endpoint allows resource exhaustion via zip bomb and file size limit bypass in Mattermost

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-13 · updated 2026-09-14
Weakness: CWE-409

Description

Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22 fail to limit decompressed content size and enforce the configured maximum file size in the Boards archive import handler, which allows an authenticated user to cause memory exhaustion or unbounded disk consumption via a crafted .boardarchive file uploaded to the import endpoint.. Mattermost Advisory ID: MMSA-2026-00713

Affected products

Mattermost: from 10.11.0 before 10.11.23; from 11.7.0 before 11.7.8; from 11.8.0 before 11.8.5; from 11.9.0 before 11.9.1 — fixed in 10.11.23, 11.7.8, 11.8.5, 11.9.1

How to fix

Upgrade to a fixed version: Mattermost 10.11.23, 11.7.8, 11.8.5, 11.9.1. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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