CVE-2026-4858: Path traversal in integration action URL leading to arbitrary API execution via system admin’s auth token.

Severity: critical (CVSS 9.9 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-21 · updated 2026-07-23
Weakness: CWE-22

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 check integration URL for path traversal which allows an malicious authenticated user to call an arbitrary API via system admin Mattermost auth token using via path traversal in integration action URL.. Mattermost Advisory ID: MMSA-2026-00640

Affected products

Mattermost: from 10.11.0 before 10.11.15; from 11.4.0 before 11.4.5; from 11.5.0 before 11.5.4; 11.6.0 — fixed in 10.11.15, 11.4.5, 11.5.4

How to fix

Upgrade to a fixed version: Mattermost 10.11.15, 11.4.5, 11.5.4. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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