Quick answers
- Is This vulnerability exploited in the wild?
- No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.
- How severe is This vulnerability?
- Medium severity, with a CVSS score of 6.5, published 15 October 2026.
- Which products and versions are affected?
- Nodemailer 3.0.0 through 10.0.9; nodemailer (npm) >= 3.0.0, <= 10.0.9, SEMVER:introduced=3.0.0,last_affected=10.0.9.
- Is there a fix for This vulnerability?
- Yes: fixed in 10.0.10. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is This vulnerability attacked?
- It is attacked over the network, in a software library.
- Am I affected?
- Check whether you run 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
- Fixed in: 10.0.10
Technical details
The MessageParser.parseHeaders function in src/dkim/message-parser.ts unfolds RFC 5322 header continuation lines with quadratic complexity: it concatenates continuation lines in a loop and re-tests an anchored regex against the growing merged line on each iteration, forcing a full string flatten proportional to accumulated length. An attacker who controls message headers (especially large recipient lists) can force tens of thousands of continuation lines and block the single-threaded Node.js event loop for seconds during DKIM signing.
Affected products
- Nodemailer Nodemailer 3.0.0 through 10.0.9
Timeline
- 2026-09-30: disclosed
- 2026-10-14: advisory
- 2026-10-15: patched