Vulnerability · Published Sep 26, 2026 · Assigned by VulnCheck
CVE-2026-100699Nodemailer before 10.0.9 Malformed Envelope Recipient via RFC 5322 Comment
Medium 5.3
In plain English
A medium-severity improper input validation in nodemailer from nodemailer. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 14% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
Nodemailer is a Node.js email-sending library. In versions >= 9.1.0 and < 10.0.9, the address parser (src/addressparser) mishandles addresses whose local-part is a quoted string and that are followed by RFC 5322 comments, allowing trailing comment-separated domain atoms to be retained in the normalized address. For example, the input "user"@example.com(x)evil.com is parsed to the address value 'user@example.com evil.com', which contains additional attacker-controlled domain text separated by a literal space. This parsed value is used without further strict recipient validation when the message envelope is built (envelope.to in src/mime-node), so a malformed/ambiguous recipient address can be accepted and placed in the SMTP envelope. Whether this results in delivery to an unintended recipient on real SMTP servers has not been confirmed. The issue is a variant of the RFC 5322 comment parsing problem addressed in GHSA-cc9r-2j5m-2m83, affecting the separate quoted-local-part code path. Version 10.0.9 contains a fix.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | node-nodemailer | no fix listed | DEBIAN-CVE-2026-100699 |
| Debian:13 | node-nodemailer | no fix listed | DEBIAN-CVE-2026-100699 |
| Debian:14 | node-nodemailer | 10.0.10+~8.0.1-1 | DEBIAN-CVE-2026-100699 |
| Ubuntu:22.04:LTS | node-nodemailer | no fix listed | UBUNTU-CVE-2026-100699 |
| Ubuntu:24.04:LTS | node-nodemailer | no fix listed | UBUNTU-CVE-2026-100699 |
| Ubuntu:26.04:LTS | node-nodemailer | no fix listed | UBUNTU-CVE-2026-100699 |
| Ubuntu:26.10 | node-nodemailer | no fix listed | UBUNTU-CVE-2026-100699 |
| npm | nodemailer | 10.0.9 | GHSA-g57g-f23g-4646 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| nodemailer | nodemailer | 9.1.0 – before 10.0.9 |
Weakness: CWE-20 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
References
- GitHub Security Advisory (GHSA-g57g-f23g-4646) vendor-advisory
- VulnCheck Advisory: Nodemailer before 10.0.9 Malformed Envelope Recipient via RFC 5322 Comment third-party-advisory