# CVE-2026-110872: Nodemailer SMTP parser denial of service

Source: https://junglewise.ai/threats/cve-2026-110872-nodemailer-from-3-0-0-before-10-0-10-contains-a-quadratic  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-14. Updated: 2026-10-16  
License: CC BY 4.0 with a link back

CVE-2026-110872 · Severity: medium · CVSS 5.9 · Published 2026-10-14

Nodemailer is a Node.js library for sending emails via SMTP. A malicious or compromised SMTP server can freeze the entire Node.js process before authentication by streaming crafted continuation lines, causing all other application work to halt. An attacker can sustain the outage indefinitely by continuing to stream data.

Technologies: [Nodemailer](https://junglewise.ai/threats/technologies/nodemailer), [nodemailer (npm)](https://junglewise.ai/threats/technologies/npm-nodemailer). Vendors: [Nodemailer](https://junglewise.ai/threats/vendors/nodemailer), [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2026-110872 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-110872 being exploited in the wild.

**How severe is CVE-2026-110872?** Medium severity, with a CVSS score of 5.9, published 14 October 2026.

**Which products and versions are affected?** Nodemailer 3.0.0 through 10.0.9; nodemailer (npm) SEMVER:introduced=3.0.0,fixed=10.0.10.

**Is there a fix for CVE-2026-110872?** Yes. nodemailer (npm): upgrade to 10.0.10 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-110872 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-110872?** 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

- nodemailer (npm): upgrade to 10.0.10 or later

  ```sh
  npm install nodemailer@10.0.10
  ```


## Technical details

The vulnerability is a quadratic (O(n²)) complexity flaw in the SMTP client reply parser (SMTPConnection._onData and isPartialResponse) that reassembles multiline server replies. When processing continuation lines without a completion line, the parser repeatedly performs string slice and test operations on an unbounded accumulated reply buffer, forcing full string flattens on each line. This stalls the single-threaded Node.js event loop during the greeting/EHLO phase, before authentication, with no size or line-count limit.

## Affected products

- nodemailer nodemailer 3.0.0 through 10.0.9

## Identifiers

- CVE-2026-110872
- GHSA-4g23-2xm8-66gc

## Timeline

- 2026-09-30: disclosed
- 2026-10-14: advisory

## References

- [https://github.com/nodemailer/nodemailer/security/advisories/GHSA-4g23-2xm8-66gc](https://github.com/nodemailer/nodemailer/security/advisories/GHSA-4g23-2xm8-66gc)
- [https://www.vulncheck.com/advisories/nodemailer-3.0.0-before-10.0.10-denial-of-service-via-smtp-reply-parsing](https://www.vulncheck.com/advisories/nodemailer-3.0.0-before-10.0.10-denial-of-service-via-smtp-reply-parsing)

## Related threats

- [Nodemailer address parsing bypass in addressparser](https://junglewise.ai/threats/cve-2026-125755-nodemailer-3-0-0-before-10-4-1-contains-an-address-parsing-flaw)
- [Nodemailer address parsing bypass in nested RFC 5322 comments](https://junglewise.ai/threats/cve-2026-121424-nodemailer-from-3-0-0-before-10-1-4-contains-an-address-parsing)
- [Nodemailer addressparser RFC 5322 comment parsing bypass](https://junglewise.ai/threats/nodemailer-a-nested-comment-ends-early-in-addressparser-releasing-the-4e80613c)
- [Nodemailer addressparser group terminator bypass in quoted strings](https://junglewise.ai/threats/nodemailer-a-inside-a-quoted-string-or-comment-ends-an-address-group-b8b045f9)
- [Nodemailer addressparser angle-addr parsing bypass](https://junglewise.ai/threats/nodemailer-a-inside-a-quoted-local-part-ends-an-angle-addr-early-in-28663cfb)