CVE-2026-110871: Nodemailer 3.0.0 before 10.0.10 Quadratic DKIM Header Unfolding Denial of Service
Nodemailer from 3.0.0 before 10.0.10 contains a denial of service vulnerability in MessageParser.parseHeaders that allows users to exhaust CPU through quadratic header unfolding. Attackers can supply large recipient lists or long headers that fold into tens of thousands of continuation lines, blocking the Node.js event loop during DKIM signing.
Affected Software
Event History
Frequently Asked Questions
Which deployments are exposed to this issue?
Deployments using the npm/nodemailer package from version 3.0.0 up to, but not including, 10.0.10 are affected. The vulnerable processing occurs during DKIM signing.
What does an attacker need to do to trigger the denial of service?
An attacker needs the ability to supply large recipient lists or long headers that are folded into tens of thousands of continuation lines. Processing those headers can consume CPU and block the Node.js event loop.
What is the operational impact of successful exploitation?
Successful exploitation exhausts CPU during header parsing for DKIM signing and can block the Node.js event loop. This results in a denial of service; no confidentiality or integrity impact is identified in the provided vector.