CVE-2026-100699: Nodemailer address parser malformed recipient in RFC 5322 comments

CVE-2026-100699 · Severity: medium · CVSS 5.3 · Published 2026-09-26

Nodemailer is a Node.js library that sends emails on behalf of applications. A parsing flaw in versions 9.1.0 through 10.0.8 allows attackers to inject malformed recipient addresses by exploiting RFC 5322 comment syntax, potentially causing emails to be sent to unintended recipients or triggering unexpected behavior in SMTP server processing.

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

Quick answers

Is CVE-2026-100699 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-100699 being exploited in the wild.
How severe is CVE-2026-100699?
Medium severity, with a CVSS score of 5.3, published 26 September 2026.
Which products and versions are affected?
Nodemailer Project Nodemailer >=9.1.0, <10.0.9; nodemailer (npm) SEMVER:introduced=9.1.0,fixed=10.0.9.
Is there a fix for CVE-2026-100699?
Yes. nodemailer (npm): upgrade to 10.0.9 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-100699 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-100699?
Check whether you run Nodemailer Project 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 10.0.9 or later
    npm install nodemailer@10.0.9

Technical details

The address parser fails to properly sanitize quoted local-parts followed by RFC 5322 comments, retaining attacker-controlled domain fragments in the normalized address (e.g., "user"@example.com(x)evil.com becomes user@example.com evil.com). This malformed address is propagated directly into the SMTP envelope without additional validation. Network-based attacker with no privileges required can supply crafted email addresses; confirmed impact is malformed recipient acceptance, though end-to-end SMTP delivery impact is not yet confirmed.

Affected products

  • Nodemailer Project Nodemailer >=9.1.0, <10.0.9

Identifiers

  • CVE-2026-100699
  • GHSA-g57g-f23g-4646

Timeline

  • 2026-09-26: disclosed
  • 2026-09-26: patched: Version 10.0.9 contains the fix

References

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