CVE-2026-9602: Mattermost Desktop App versions <=6.2 6.0.2 5.6.13.0 fail to validate payloads sent from the Mattermost Web Ap

Q: How urgent is CVE-2026-9602?

Priority 32/100. No elevated risk signals yet.

Routine

MEDIUM 6.5UPGRADE

CVE-2026-9602 is a medium-severity flaw (CVSS 6.5) affecting mattermost desktop. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Mattermost Desktop App versions <=6.2 6.0.2 5.6.13.0 fail to validate payloads sent from the Mattermost Web App to the Desktop App which allows a malicious server owner to crash the Mattermost Desktop App via changing the payload of a method to a malformed one. Mattermost Advisory ID: MMSA-2026-00678

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	6.5 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.4% (top 64%)
CISA exploited list	No
Weakness	CWE-400
Published	2026-07-17
Last modified	2026-10-15

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

Last updated 2026-10-15 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-17 11:17 UTCPublished CVE record published
2026-10-15 13:32 UTCUpdated Record last modified

mattermost mattermost desktop UPGRADE

Affected: < 5.13.7 · >= 6.0.0 and <= 6.0.2 · >= 6.2.0 and < 6.2.1

Fixed in: 5.13.7, 6.2.1

Safe to downgrade to: a release before 6.0.0

1. Check installed version

apt-cache policy mattermost-desktop || rpm -q mattermost-desktop || mattermost-desktop --version

2. UPGRADE to 5.13.7 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade mattermost-desktop

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade mattermost-desktop

Note

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

3. If no update is available yet, DOWNGRADE to a release before 6.0.0 (Debian / Ubuntu)

apt-cache madison mattermost-desktop sudo apt install mattermost-desktop=<VERSION_BEFORE_6.0.0> sudo apt-mark hold mattermost-desktop

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list mattermost-desktop sudo dnf downgrade mattermost-desktop-<VERSION_BEFORE_6.0.0> sudo dnf versionlock add mattermost-desktop

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

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-2026-9602?

mattermost desktop: upgrade to 5.13.7, 6.2.1. Exact commands for each OS are on this page.

Is CVE-2026-9602 being exploited?

CVE-2026-9602 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-2026-9602 affect?

CVE-2026-9602 affects mattermost desktop. Severity is medium (CVSS 6.5). Mattermost Desktop App versions <=6.2 6.0.2 5.6.13.0 fail to validate payloads sent from the Mattermost Web App to the Desktop App which allows a malicious server owner to crash the Mattermost Desktop App via changing the payload of a metho

How urgent is CVE-2026-9602?

Priority 32/100. No elevated risk signals yet.

Software pages

Mattermost vulnerabilities

Related CVEs

CVE-2026-8075 MEDIUM 6.5 UPGRADE Mattermost Desktop App versions <=6.2 5.5.13 6.0.2.0 fail to properly null check when checking for headers in
CVE-2026-75025 MEDIUM 4.7 UPGRADE Mattermost Desktop App versions <=6.2 6.2.2.0 Fixed an issue where Mattermost Desktop did not sufficiently res
CVE-2026-75587 LOW 3.6 UPGRADE Mattermost Desktop App versions <=6.2 6.2.2.0 fail to redact the pre-auth secret when generating a diagnostics

References

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