CVE-2026-14298 Mattermost CVE debrief

Who should care

Mattermost Server administrators and users who have access to the import endpoint should be aware of this vulnerability and take necessary precautions to prevent potential memory exhaustion or disk consumption.

Why it matters

CVE-2026-14298 is a vulnerability in Mattermost Server that allows an authenticated user to cause memory exhaustion or unbounded disk consumption. Defenders should prioritize verifying and updating Mattermost Server instances to prevent potential memory exhaustion or disk consumption.

• Potential memory exhaustion or unbounded disk consumption
• Possible denial of service (DoS) attacks
• Need for verification and updates to prevent exploitation

Technical summary

The vulnerability is caused by the failure to limit decompressed content size and enforce the configured maximum file size in the Boards archive import handler, allowing an authenticated user to cause memory exhaustion or unbounded disk consumption via a crafted .boardarchive file uploaded to the import endpoint. This issue affects Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, 10.11.x <= 10.11.22. Defenders should prioritize verifying and updating Mattermost Server instances to prevent potential memory exhaustion or disk consumption.

Defensive priority

Defenders should prioritize verifying and updating Mattermost Server instances to prevent potential memory exhaustion or disk consumption.

Recommended defensive actions

• Verify and update Mattermost Server instances to the latest version
• Restrict access to the import endpoint
• Monitor for suspicious .boardarchive file uploads
• 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 vulnerability is caused by the failure to limit decompressed content size and enforce the configured maximum file size in the Boards archive import handler. Evidence is based on the Mattermost Advisory ID: MMSA-2026-00713 and CVE Program records. Defenders should verify the affected versions and update to the latest version to prevent exploitation. The CVE record was published on 2026-08-13T09:17:11.860Z and has not been modified since then.

Sources and 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.