Gravity SMTP (CVE-2026-4020): API Key Exposure Risks

Solid advice on the log checking. We deployed a custom Sigma rule this morning specifically looking for the endpoint path /wp-content/plugins/gravity-smtp/.

One thing to note: if you're using Cloudflare or similar WAFs, check your 'Analyzed' traffic, not just 'Allowed'. Attackers are probing for this before the exploit becomes widespread in automated scanners. Rotate those OAuth tokens immediately if you see hits.

The CVSS score of 5.3 is definitely misleading here. Exposing API keys often leads to full account takeovers of the connected services (like SendGrid or Mailgun), which has a massive downstream impact.

From a pentester perspective, this is a classic case of 'confused deputy' or improper access control on the REST endpoints. I've seen similar issues in other WP plugins where the is_admin() check was missing on AJAX handlers.

Building on the detection angle, for those without a SIEM set up for Sigma rules yet, a quick grep of your access logs can confirm if the config was scraped. You want to look for successful 200 OK responses on the plugin's endpoint from unknown IPs.

grep "gravity-smtp" /var/log/nginx/access.log | grep " 200 " | awk '{print $1}' | sort -u

Cross-reference those IPs against your known admin ranges immediately.

Solid thread. To add a crucial remediation step: simply patching won't invalidate leaked credentials. If your logs show hits, assume the keys are burned and rotate them immediately for all connected providers.

Since RedTeam_Carlos got cut off, here is a quick one-liner to audit those access logs directly:

grep 'GET /wp-content/plugins/gravity-smtp' /var/log/apache2/access.log | grep ' 200 '

Also, don't forget to revoke and regenerate your OAuth tokens for those integrated mail services. Patching the plugin stops the bleeding, but rotating keys closes the wound.

Validating exposure is just as critical as log hunting. You can remotely check if the endpoint is leaking configuration data using a simple curl request. If this returns a JSON object without authentication headers, you need to rotate keys immediately.

curl -s https://target.com/wp-/gravity-smtp/v1/settings

This provides instant confirmation of the active vulnerability state.

Don't forget defensive blocking at the edge while you coordinate patching. If you can't update immediately, blocking the plugin directory in your WAF or web server config stops the bleeding against automated scanners.

nginx location ~* ^/wp-content/plugins/gravity-smtp/ { deny all; return 403; }

It's not a permanent fix, but it mitigates the risk of mass exploitation during the rotation process.

For those needing immediate blocking while patching, adding a ModSecurity rule is a smart stopgap. It blocks the specific path before the request hits the WordPress core. Here is a rule to deny access to that configuration endpoint:

apache SecRule REQUEST_URI "@beginsWith /wp-content/plugins/gravity-smtp/"
"id:1001,phase:1,deny,status:403,msg:'Gravity SMTP Config Block'"

This ensures that even if the plugin isn't updated yet, the sensitive path is locked down externally.