CVE-2026-14298 Mattermost CVE debrief

Who should care

Defenders responsible for Mattermost installations should assess exposure and prioritize verification and updates to prevent potential attacks. This includes reviewing system logs for signs of exploitation, restricting access to the Boards archive import endpoint, and ensuring that installations are running a version that addresses the vulnerability. Additionally, defenders should consider implementing compensating controls for exposed systems and tracking

Why it matters

CVE-2026-14298 is a vulnerability in Mattermost's Boards archive import handler that allows authenticated users to cause memory exhaustion or unbounded disk consumption. Defenders responsible for Mattermost installations should assess exposure and prioritize verification and updates to prevent potential attacks.

• Memory exhaustion or unbounded disk consumption can lead to denial-of-service conditions.
• Authenticated users can exploit the vulnerability to cause potential attacks.
• Verification and updates are necessary to prevent potential attacks.

Technical summary

The vulnerability is caused by the failure of the Boards archive import handler to limit decompressed content size and enforce the configured maximum file size. This allows an authenticated user to upload a crafted .boardarchive file that can cause memory exhaustion or unbounded disk consumption. The issue affects Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.7, and 10.11.x <= 10.11.22, and can lead to denial-of-service conditions if exploited. Defenders should prioritize verifying and updating Mattermost installations to prevent potential attacks.

Defensive priority

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

Recommended defensive actions

• Verify and update Mattermost installations to ensure they are running a version that addresses the vulnerability.
• Restrict access to the Boards archive import endpoint to only trusted users.
• Monitor Mattermost installations for potential memory exhaustion or disk consumption attacks.
• 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 described in the CVE Program record and the NVD vulnerability detail page. The vendor advisory is available on the Mattermost security updates page. Evidence is limited to public sources and may not reflect the full scope or impact of the vulnerability. Defenders should verify the vulnerability's existence and impact within their specific environments.

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.