Threat actors are exploiting a recently patched security flaw impacting Gravity SMTP, a WordPress plugin that's installed on about 100,000 sites.
The vulnerability, tracked as CVE-2026-4020 (CVSS score: 5.3), is a medium-severity information disclosure flaw that can allow unauthenticated attackers to extract sensitive data, such as configuration data, API keys, secrets, and OAuth tokens configured for the plugin's email integrations.
"This is due to a REST API endpoint registered at /wp-json/gravitysmtp/v1/tests/mock-data with a permission_callback that unconditionally returns true, allowing any unauthenticated visitor to access it," Wordfence said.
"When the ?page=gravitysmtp-settings query parameter is appended, the plugin's register_connector_data() method populates internal connector data, causing the endpoint to return approximately 365 KB of JSON containing the full System Report."
As a result, an unauthenticated attacker can weaponize this issue to retrieve a wide range of information, including -
- PHP version
- Loaded extensions
- Web server version
- Document root path
- Database server type and version
- WordPress version
- All active plugins with versions
- Active theme
- WordPress configuration details
- Database table names
- API keys/tokens configured in the plugin, such as Amazon SES, Google, Mailjet, Resend, and Zoho
Attackers could then leverage this exposure to harvest credentials that could be abused to send email on behalf of the site, as well as glean extensive details of the site's software stack, which could act as a foundation for follow-on attacks.
"As with all sensitive information exposure vulnerabilities, the impact depends on what data is exposed," Wordfence added. "In this case, the exposure of live third-party API credentials means an attacker could abuse the site's connected email services, while the detailed system report significantly lowers the effort required to plan further attacks against the site."
A patch for the vulnerability has been released in version 2.1.5 of the plugin. Bad actors have already pounced on the defect by sending unauthenticated HTTP GET requests to the vulnerable REST API endpoint with the "?page=gravitysmtp-settings" query parameter, causing the server to return valuable information about the site without requiring any authentication.
Wordfence has blocked more than 17 million exploit attempts targeting CVE-2026-4020 to date, with initial activity commencing at the start of May 2026 before spiking up dramatically around June 6, 2026, touching a high of over 4,000,000 requests a day later. The exploit efforts have originated from the following IP addresses -
- 45.148.10.95
- 193.32.162.60
- 176.65.148.139
- 173.199.90.188
- 45.148.10.120
- 185.8.107.155
- 185.8.106.37
- 185.8.106.92
- 185.8.106.145
- 176.65.148.30
Site owners running a vulnerable version of the Gravity SMTP plugin and have configured third-party email integrations should assume compromise, and rotate the credentials after updating the plugin to the latest version as soon as possible. It's also advised to review server log files for requests originating from the aforementioned IP addresses for any suspicious requests to the API endpoint.
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