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CVE-2026-9602 Mattermost CVE debrief

CVE-2026-9602 is a medium-severity vulnerability in Mattermost Desktop App versions <=6.2, 6.0.2, 5.6.13.0. The vulnerability allows a malicious server owner to crash the Mattermost Desktop App by changing the payload of a method to a malformed one. This issue arises from the app's failure to validate payloads sent from the Mattermost Web App to the Desktop App. Users of affected versions should be aware of this vulnerability and take necessary actions to mitigate the risk.

Vendor
Mattermost
Product
Unknown
CVSS
MEDIUM 6.5
CISA KEV
Not listed in stored evidence
Original CVE published
2026-07-17
Original CVE updated
2026-07-30
Advisory published
2026-07-17
Advisory updated
2026-07-30

Who should care

Users of Mattermost Desktop App versions <=6.2, 6.0.2, 5.6.13.0 should be aware of this vulnerability and take necessary actions to mitigate the risk. This includes updating to a version that is not vulnerable, verifying the authenticity of payloads received from the Mattermost Web App, and monitoring the Mattermost Desktop App for crashes or unusual behavior.

Technical summary

The Mattermost Desktop App fails to validate payloads sent from the Mattermost Web App to the Desktop App. This allows a malicious server owner to crash the Mattermost Desktop App via changing the payload of a method to a malformed one. The vulnerability affects versions <=6.2, 6.0.2, 5.6.13.0 of the Mattermost Desktop App. Users should update to a non-vulnerable version and verify payload authenticity.

Defensive priority

Medium

Recommended defensive actions

  • Update Mattermost Desktop App to a version that is not vulnerable
  • Verify the authenticity of payloads received from the Mattermost Web App
  • Monitor the Mattermost Desktop App for crashes or unusual behavior
  • Review compensating controls for exposed systems while remediation is scheduled and verified
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review
  • Track exceptions, retest remediated assets, and close the item only after evidence is documented
  • Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record was published on 2026-07-17T11:17:15.297Z and has not been modified since then. The NVD entry is currently in the 'Received' status. The vulnerability affects Mattermost Desktop App versions <=6.2, 6.0.2, 5.6.13.0. Users should verify the authenticity of payloads received from the Mattermost Web App and monitor the Mattermost Desktop App for crashes or unusual behavior.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-9602 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-9602

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-9602 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-9602

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.