CVE-2026-13426: Client4 fails to validate path parameters

Severity: medium (CVSS 5.4 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: 2026-06-26 · updated 2026-10-25
Weakness: CWE-22

Description

The Mattermost Go module github.com/mattermost/mattermost/server/public versions < v0.1.22 fail to validate path parameters when constructing API route paths which allows an attacker to redirect API calls to unintended endpoints via crafted IDs containing path traversal components. Mattermost Advisory ID: MMSA-2025-00532

Affected products

Mattermost github.com/mattermost/mattermost/server/public: from v0.0.0 before v0.1.22 — fixed in v0.1.22

How to fix

Upgrade to a fixed version: Mattermost github.com/mattermost/mattermost/server/public v0.1.22. Check the vendor advisory for mitigations.

References

https://mattermost.com/security-updates

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