CVE-2026-6961 — Vulnerability in...

HIGH

Mattermost doesn't sanitize FileInfo.Name received from federated peers during shared channel file sync

Published June 12, 2026Updated August 26, 2026Source: osv

Summary

Mattermost versions 11.6.x <= 11.6.1, 11.5.x <= 11.5.4, 10.11.x <= 10.11.15, 10.11.x <= 10.11.16 fail to sanitize FileInfo.Name received from federated peers during shared channel file sync, which allows an attacker who controls a federated server to write files to arbitrary locations within the target server's filestore via path traversal sequences in the filename field. Mattermost Advisory ID: MMSA-2026-00661

Advisory Timeline

First published June 12, 2026 (122 days ago).
Last revised August 26, 2026 — 74 days after initial publication.

Remediation

Upgrade to the fixed version using your package manager.

Update github.com/mattermost/mattermost-server to 11.5.5 or later

go get github.com/mattermost/mattermost-server@v11.5.5

Update github.com/mattermost/mattermost-server to 10.11.17 or later

go get github.com/mattermost/mattermost-server@v10.11.17

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/v8 to 8.0.0-20260423180926-c021eeaff8f0 or later

go get github.com/mattermost/mattermost/server/v8@v8.0.0-20260423180926-c021eeaff8f0

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

Affected Packages (4)

Affects 1 ecosystem: go (2).

Package	Ecosystem	Affected	Fixed In
github.com/mattermost/mattermost-server	go	All versions	11.5.5
github.com/mattermost/mattermost-server	go	All versions	10.11.17
github.com/mattermost/mattermost-server	go	11.6.0	11.6.1
github.com/mattermost/mattermost/server/v8	go	All versions	8.0.0-20260423180926-c021eeaff8f0

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) 7.6 score means for each attack dimension.

Attack Vector

Network

Attack Complexity

Low

Privileges Required

High

User Interaction

None

Scope

Changed

Confidentiality

None

Integrity

High

Availability

Low

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

References

Frequently Asked Questions

What is CVE-2026-6961?: Mattermost doesn't sanitize FileInfo.Name received from federated peers during shared channel file sync This vulnerability has been assigned a severity rating of HIGH (CVSS score: 7.6/10).
How do I check if my project is affected by CVE-2026-6961?: CVE-2026-6961 affects github.com/mattermost/mattermost-server and github.com/mattermost/mattermost/server/v8. Use GeekWala's free vulnerability scanner to check your dependencies against CVE-2026-6961 and 200,000+ other known vulnerabilities.

Severity & Exploitability

CVSS Score

7.6

High exploitability or significant impact. Prioritize remediation within days.

Also Known As

GHSA-8qq9-cqj8-82w4

GO-2026-6281

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