Attack Chain

1. An application configured to use Nodemailer with disableFileAccess and/or disableUrlAccess for sandboxing processes untrusted user input.
2. An attacker crafts malicious input for the transporter.sendMail() call, specifically targeting the raw message option.
3. The attacker's input includes a malicious path (e.g., raw: { path: '/etc/passwd' }) or a malicious URL (e.g., raw: { href: 'http://169.254.169.254/latest/meta-data/' }).
4. Nodemailer's MailComposer.compile() function creates the root MIME node for the raw message without correctly applying the disableFileAccess/disableUrlAccess flags.
5. The MimeNode constructor initializes these flags to false by default, effectively ignoring the application's intended sandboxing.
6. During message compilation, setRaw() calls _getStream(), which proceeds to read the specified local file or fetch the specified URL, as the security flags are inactive.
7. The entire content of the read file or the fetched HTTP response body becomes the actual message content of the email.
8. Nodemailer's transport mechanisms deliver this crafted email, containing sensitive server data, to an email address specified by the attacker (e.g., attacker@evil.test).

Impact

The primary impact of this vulnerability is a high compromise of data confidentiality. Attackers can exfiltrate arbitrary local files from the server, such as /etc/passwd, /proc/self/environ, application .env files, or key material. Additionally, the full-response SSRF capability allows attackers to query internal network services or cloud metadata endpoints (e.g., 169.254.169.254) and retrieve their full responses. This sensitive information is then delivered directly to an attacker-controlled mailbox, making internal data accessible to external adversaries. The vulnerability directly subverts security controls put in place by the application, rendering them ineffective for the raw message type.

Recommendation

• Patch: Immediately update Nodemailer to a patched version once available. Monitor the official Nodemailer repository and npm for security releases addressing GHSA-p6gq-j5cr-w38f.
• Application-level mitigation: Review all code paths that use transporter.sendMail() with the raw option. Ensure that untrusted user input cannot directly influence the path or href properties within the raw object. Implement strict input validation and sanitization.
• Deployment: Deploy the provided Sigma rules to your SIEM/EDR to detect attempts at SSRF and suspicious file access by Node.js processes on Linux hosts.
• Logging: Ensure comprehensive logging for process activity, file access, and network connections on servers hosting Node.js applications, particularly on Linux systems, to facilitate detection and investigation.