CVE-2026-100700 nodemailer before 10.0.6 Denial of Service via addressparser
Attackers can cause service unavailability in applications using nodemailer by sending crafted email headers that trigger quadratic backtracking in the address parser.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-100700?
CVE-2026-100700 is a high-severity denial of service 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 before 10.0.6 contains a denial of service vulnerability in the addressparser free-text fallback regex pattern that exhibits quadratic backtracking behavior. Attackers can supply crafted email header values with long whitespace-free runs to block the Node.js event loop for tens of seconds, causing service unavailability.
Weakness: CWE-407
Which versions are affected by CVE-2026-100700?
2 open source packages ship an affected version, including nodemailer.
| Package | Affected | Fixed in |
|---|---|---|
nodemailer npm | All versions | 10.0.6 |
nodemailer npm | All versions | 10.0.6 |
How do I fix CVE-2026-100700?
Upgrade nodemailer to 10.0.6 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-100700 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-100700 exists.
Sources
Also known as CLEANSTART-2026-TF67496, CLEANSTART-2026-UX56548, CLSA-2026-1790863073, CLSA-2026-1790937712, CLSA-2026-1791028046, DEBIAN-CVE-2026-100700 and 20 more.