Nodemailer addressparser RFC 5322 comment parsing bypass

Severity: medium · CVSS 6.5 · Published 2026-10-23

Nodemailer's email address parser incorrectly handles nested comments in RFC 5322 addresses, allowing an attacker to bypass recipient validation and redirect mail to an attacker-controlled domain. An application that validates addresses and restricts recipients to approved domains can be tricked into sending to an unauthorized recipient, exposing the message content. Additionally, inbound message parsing can report a different sender than conformant parsers, enabling sender spoofing in display and authentication contexts.

Technologies: Nodemailer, nodemailer (npm). Vendors: Nodemailer, npm.

Quick answers

Is This vulnerability exploited in the wild?
No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.
How severe is This vulnerability?
Medium severity, with a CVSS score of 6.5, published 23 October 2026.
Which products and versions are affected?
Nodemailer 3.0.0 through 10.1.3; nodemailer (npm) >= 3.0.0, < 10.1.4, SEMVER:introduced=3.0.0,fixed=10.1.4.
Is there a fix for This vulnerability?
Yes. nodemailer (npm): upgrade to 10.1.4 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is This vulnerability attacked?
It is attacked over the network, in a software library.
Am I affected?
Check whether you run Nodemailer or nodemailer (npm) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • nodemailer (npm): upgrade to 10.1.4 or later
    npm install nodemailer@10.1.4

Technical details

The addressparser module terminates RFC 5322 comments at the first closing parenthesis, rather than counting nesting depth to find the matching one. An attacker can craft a syntactically valid address like `Victim (x(y) <evil@evil.com>) <v@victim.com>` that passes conformant RFC 5322 validators but is misparsed as `evil@evil.com` by Nodemailer. The vulnerability affects outbound mail delivery via sendMail() and inbound message parsing via mailparser, both of which rely on the same vulnerable addressparser logic.

Affected products

  • Nodemailer Nodemailer 3.0.0 through 10.1.3

Timeline

  • 2026-10-18: disclosed: Found in internal review
  • 2026-10-23: advisory

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