CVE-2026-86813 MetForm CVE debrief

Who should care

Defenders responsible for WordPress sites using the MetForm plugin should assess exposure and prioritize updating the plugin to version 4.1.9 or later. They should also review email configurations and monitor email headers for potential injections. Security teams and vulnerability management teams should be aware of this vulnerability and its potential impact.

Why it matters

CVE-2026-86813 allows unauthenticated attackers to inject additional email headers in WordPress sites using the MetForm plugin before version 4.1.9. Defenders should prioritize updating the plugin and monitoring email headers.

• Potential email header injection allows for unauthorized Bcc or other header modifications
• Requires verification of plugin version and email configuration to prevent exploitation
• Defenders should monitor email headers for potential injections

Technical summary

The MetForm WordPress plugin before 4.1.9 does not properly neutralize newline characters in user-submitted values that are placed into notification email headers, allowing unauthenticated attackers to inject additional email headers, such as Bcc, into the emails the site sends when a submitted field value is configured to populate a header. This vulnerability affects WordPress sites using the MetForm plugin, particularly those with email notifications configured. The vulnerability allows for potential email header injection.

Defensive priority

Defenders should prioritize verifying and updating the MetForm WordPress plugin to version 4.1.9 or later, and monitor email headers for potential injections.

Recommended defensive actions

• Verify and update the MetForm WordPress plugin to version 4.1.9 or later
• Monitor email headers for potential injections
• Review and update email configuration to prevent unauthorized header injection
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Review the supplied official advisory or CVE record to validate affected scope, severity, and vendor guidance
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE record and NVD vulnerability detail page provide information on the vulnerability. Limited evidence is available on potential exploitation or impact. The vulnerability allows unauthenticated attackers to inject additional email headers. The MetForm plugin before version 4.1.9 is affected. Defenders should verify plugin version and email configuration.

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.