# CVE-2026-100702: Nodemailer stack exhaustion in recipient array flattening

Source: https://junglewise.ai/threats/cve-2026-100702-nodemailer-before-10-0-2-fails-to-properly-flatten-deeply-nested  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-26. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-100702 · Severity: medium · CVSS 5.9 · Published 2026-09-26

Nodemailer, a Node.js email library, fails to properly flatten deeply nested arrays in recipient fields (to, cc, bcc), allowing attackers to crash the email service. An attacker can send a specially crafted JSON with nested arrays that triggers excessive recursion, exhausting the server's call stack and terminating the Node.js process, causing a denial of service that may affect email delivery or related services.

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-2026-100702 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-100702 being exploited in the wild.

**How severe is CVE-2026-100702?** Medium severity, with a CVSS score of 5.9, published 26 September 2026.

**Which products and versions are affected?** Nodemailer before 10.0.2; nodemailer (npm) SEMVER:introduced=0,fixed=10.0.2.

**Is there a fix for CVE-2026-100702?** Yes. nodemailer (npm): upgrade to 10.0.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-100702 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-100702?** 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 10.0.2 or later

  ```sh
  npm install nodemailer@10.0.2
  ```


## Technical details

The vulnerability stems from improper array flattening in the _parseAddresses() method, which only removes the outermost array layer via concat(), leaving nested arrays intact. When addressparser() processes remaining nested arrays, it calls Array.toString() which recursively descends through all nested levels until the V8 call stack is exhausted. The attack requires network access and no authentication; a ~10 KB payload with 5,000-deep nesting triggers RangeError: Maximum call stack size exceeded during synchronous sendMail() invocation before SMTP transport is reached.

## Affected products

- Nodemailer Nodemailer before 10.0.2

## Identifiers

- CVE-2026-100702
- GHSA-8vvx-rff5-p5rq

## Timeline

- 2026-09-26: disclosed: CVE-2026-100702 and GHSA-8vvx-rff5-p5rq published
- 2026-09-26: patched: Patched in version 10.0.2

## References

- [https://github.com/nodemailer/nodemailer/security/advisories/GHSA-8vvx-rff5-p5rq](https://github.com/nodemailer/nodemailer/security/advisories/GHSA-8vvx-rff5-p5rq)
- [https://www.vulncheck.com/advisories/nodemailer-before-10.0.2-stack-exhaustion-via-nested-recipient-arrays](https://www.vulncheck.com/advisories/nodemailer-before-10.0.2-stack-exhaustion-via-nested-recipient-arrays)

## 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)