CVE-2026-6957: Mattermost Plugins versions <=1.1.5 fail to sanitize filenames received from federated peers before using them

Q: How do I fix CVE-2026-6957?

legal hold: upgrade to newer than 1.1.5. Exact commands for each OS are on this page.

Q: Is CVE-2026-6957 being exploited?

CVE-2026-6957 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-6957 affect?

CVE-2026-6957 affects legal hold. Severity is high (CVSS 8.0). Mattermost Plugins versions <=1.1.5 fail to sanitize filenames received from federated peers before using them to construct export destination paths, which allows an administrator of a remote federated Mattermost server to write files to ar

Routine

HIGH 8.0UPGRADE

CVE-2026-6957 is a high-severity flaw (CVSS 8.0) affecting legal hold. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Mattermost Plugins versions <=1.1.5 fail to sanitize filenames received from federated peers before using them to construct export destination paths, which allows an administrator of a remote federated Mattermost server to write files to arbitrary locations within the target server's filestore via a malicious filename delivered through the shared-channel attachment sync protocol. Mattermost Advisory ID: MMSA-2026-00659

Why this priority

High severity

A fixed release or distro patch exists.

Risk facts

CVSS score	8.0 (High)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	High
User interaction	None
EPSS exploit chance	0.3% (top 78%)
CISA exploited list	No
Weakness	CWE-22
Published	2026-05-27
Last modified	2026-06-17

Publisher (CNA): Mattermost, Inc. · Vendor: mattermost

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-27 15:16 UTCPublished CVE record published
2026-06-17 11:01 UTCUpdated Record last modified

mattermost legal hold UPGRADE

Affected: <= 1.1.5

Fixed in: newer than 1.1.5

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy legal-hold || rpm -q legal-hold || legal-hold --version

2. UPGRADE to newer than 1.1.5 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade legal-hold

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade legal-hold

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-6957?

legal hold: upgrade to newer than 1.1.5. Exact commands for each OS are on this page.

Is CVE-2026-6957 being exploited?

CVE-2026-6957 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-6957 affect?

CVE-2026-6957 affects legal hold. Severity is high (CVSS 8.0). Mattermost Plugins versions <=1.1.5 fail to sanitize filenames received from federated peers before using them to construct export destination paths, which allows an administrator of a remote federated Mattermost server to write files to ar

How urgent is CVE-2026-6957?

Priority 34/100. High severity

Software pages

Mattermost vulnerabilities

References

← Back to latest CVEs