CVE-2026-4858 — Vulnerability in...

HIGH

Mattermost has a Path Traversal issue

Published May 21, 2026Updated June 25, 2026Source: osv

Summary

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.

Advisory Timeline

First published May 21, 2026 (144 days ago).
Last revised June 25, 2026 — 35 days after initial publication.

Remediation

Upgrade to the fixed version using your package manager.

Update github.com/mattermost/mattermost-server to 10.11.15 or later

go get github.com/mattermost/mattermost-server@v10.11.15

Update github.com/mattermost/mattermost-server to 11.6.1 or later

go get github.com/mattermost/mattermost-server@v11.6.1

Update github.com/mattermost/mattermost-server to 11.5.4 or later

go get github.com/mattermost/mattermost-server@v11.5.4

Update github.com/mattermost/mattermost-server to 11.4.5 or later

go get github.com/mattermost/mattermost-server@v11.4.5

After upgrading, run your dependency scanner again to confirm the vulnerability is resolved.

Affected Packages (4)

Affects 1 ecosystem: go (1).

Package	Ecosystem	Affected	Fixed In
github.com/mattermost/mattermost-server	go	All versions	10.11.15
github.com/mattermost/mattermost-server	go	11.6.0	11.6.1
github.com/mattermost/mattermost-server	go	All versions	11.5.4
github.com/mattermost/mattermost-server	go	All versions	11.4.5

Vulnerability Classification

Common Weakness Enumeration (CWE) identifiers for this vulnerability type.

CWE-22
Path TraversalMITRE

CVSS Score Breakdown

What the CVSS (Common Vulnerability Scoring System) 8.0 score means for each attack dimension.

Attack Vector

Network

Attack Complexity

High

Privileges Required

Low

User Interaction

Required

Scope

Changed

Confidentiality

High

Integrity

High

Availability

High

CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:C/C:H/I:H/A:H

References

https://nvd.nist.gov/vuln/detail/CVE-2026-4858
ADVISORY
https://github.com/mattermost/mattermost
PACKAGE
https://mattermost.com/security-updates
WEB

Frequently Asked Questions

What is CVE-2026-4858?: Mattermost has a Path Traversal issue This vulnerability has been assigned a severity rating of HIGH (CVSS score: 8.0/10).
How do I check if my project is affected by CVE-2026-4858?: CVE-2026-4858 affects github.com/mattermost/mattermost-server. Use GeekWala's free vulnerability scanner to check your dependencies against CVE-2026-4858 and 200,000+ other known vulnerabilities.

Severity & Exploitability

CVSS Score

8.0

High exploitability or significant impact. Prioritize remediation within days.

Also Known As

GHSA-c4r7-j7pp-r8mp

GO-2026-5311

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