CVE-2026-100699 Nodemailer before 10.0.9 Malformed Envelope Recipient via RFC 5322 Comment
Attackers can inject malformed recipient addresses via RFC 5322 comments, potentially causing unintended email delivery or data modification.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-100699?
CVE-2026-100699 is a medium-severity vulnerability in nodemailer, published on 26 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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 '[email protected] 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.
Weakness: CWE-20
Which versions are affected by CVE-2026-100699?
2 open source packages ship an affected version, including nodemailer.
| Package | Affected | Fixed in |
|---|---|---|
nodemailer npm | From 9.1.0 | 10.0.9 |
nodemailer npm | From 9.1.0 | 10.0.9 |
How do I fix CVE-2026-100699?
Upgrade nodemailer to 10.0.9 or later.
Is CVE-2026-100699 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-100699 exists.
Sources
Also known as CLEANSTART-2026-AA77700, CLEANSTART-2026-TR78672, DEBIAN-CVE-2026-100699, ECHO-1bcb-fe8f-0e9b, GHSA-fcjc-3m4q-q926, GHSA-g57g-f23g-4646 and 4 more.