AIKIDO-2026-804227
nodemailer is vulnerable to Regular Expression Denial of Service (ReDoS)
59
Medium Risk
This Affects:
nodemailerTL;DR
Nodemailer's SMTP client checks a peer's EHLO response for supported AUTH mechanisms using four regular expressions that each contain two overlapping alternatives for matching whitespace. When the EHLO response omits a mechanism name, the regex engine tries every partition of the whitespace run before failing, producing quadratic backtracking. A malicious SMTP server or an attacker on the network path can answer EHLO with a long run of whitespace and block the Node.js event loop for a long time before authentication completes. The fix rewrites the AUTH mechanism patterns to remove the overlapping alternation.
Who does this affect?
You are affected if you are using a version that falls within the vulnerable range and you connect to an SMTP server that is untrusted or reachable by an attacker on the network path.
Background info
nodemailer is vulnerable to Regular Expression Denial of Service (ReDoS) in versions 3.0.0 - 10.0.12.
How to fix this
Upgrade the nodemailer library to the patch version.
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