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

Impact

ReDoS causes the event loop to stuck a specially crafted evil email can cause this problem.

References

• GHSA-9h6g-pr28-7cqp
• https://gist.github.com/francoatmega/890dd5053375333e40c6fdbcc8c58df6
• https://gist.github.com/francoatmega/9aab042b0b24968d7b7039818e8b2698
• nodemailer/nodemailer@dd8f5e8