MetForm permits unauthenticated notification-header injection
MetForm before 4.1.9 does not neutralize newline characters in visitor-supplied values when a form field is configured to populate a notification email header. An unauthenticated attacker can inject additional headers such as Bcc into mail sent by the site.
- Component
- MetForm
- Plugin slug
metform- Affected
- < 4.1.9
- Safe version
4.1.9- Published
- Sep 11, 2026
This CVE was published Sep 11, 2026 and is one of 24 known issues for this plugin.
Update, patch or deactivate.
Update MetForm to 4.1.9 or later. The authoritative affected data marks versions below 4.1.9 affected. The application-level fix must reject carriage returns and line feeds in all header-derived values and build mail headers through a constrained API rather than raw concatenation.
A safe version is available, so updating to that version or later is the preferred remediation. If an immediate update is not practical, consider a targeted application patch or temporarily restricting the affected functionality.
Deactivate only when warranted by your risk profile, or when advised by your hosting provider in the limited circumstances where the vulnerability cannot otherwise be mitigated. If you’re unsure which action is appropriate, contact Fused or your hosting provider for guidance.
Technical description
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.
CVE / CNA vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N