Vulnerability · Published May 21, 2026 · Assigned by Mattermost

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

High 8.0

In plain English

A high-severity path traversal in Mattermost from Mattermost. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 26% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)8.0High

Exploit odds (30 days)0.3%top 74.0% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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 packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Go	github.com/mattermost/mattermost-server	11.6.1	GHSA-c4r7-j7pp-r8mp
Go	github.com/mattermost/mattermost-server	11.5.4	GHSA-c4r7-j7pp-r8mp
Go	github.com/mattermost/mattermost-server	11.4.5	GHSA-c4r7-j7pp-r8mp
Go	github.com/mattermost/mattermost-server	10.11.15	GHSA-c4r7-j7pp-r8mp
Go	github.com/mattermost/mattermost-server	10.11.15+incompatible, 11.4.5+incompatible, 11.5.4+incompatible, 11.6.1+incompatible	GO-2026-5311

Affected products (as reported)

Vendor	Product	Versions
Mattermost	Mattermost	11.6.0 – through 11.6.011.5.0 – through 11.5.311.4.0 – through 11.4.410.11.0 – through 10.11.14

Weakness: CWE-22 · Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:H/A:H

References

MMSA-2026-00640 vendor-advisory