# CVE-2026-100701: Nodemailer TLS servername cache confusion vulnerability

Source: https://junglewise.ai/threats/cve-2026-100701-nodemailer-versions-5-0-0-through-10-0-1-use-a-process-global  
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-2026-100701 · Severity: medium · CVSS 5.9 · Published 2026-09-26

Nodemailer, a widely-used email sending library for Node.js, has a flaw in how it caches DNS lookups for SMTP connections. When multiple email transports connect to the same server using different security identities (SNI values), the library reuses cached security settings from the first connection. An attacker in a multi-tenant service can exploit this to intercept email credentials by priming the cache and forcing victim connections to accept the attacker's certificate.

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-2026-100701 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-100701 being exploited in the wild.

**How severe is CVE-2026-100701?** Medium severity, with a CVSS score of 5.9, published 26 September 2026.

**Which products and versions are affected?** Nodemailer 5.0.0 through 10.0.1; nodemailer (npm) SEMVER:introduced=5.0.0,fixed=10.0.2.

**Is there a fix for CVE-2026-100701?** 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-2026-100701 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-100701?** 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 is a cache poisoning issue in the process-global DNS cache (keyed only by hostname) that also stores caller-specific TLS servername values. When a second direct TLS/SMTPS transport (secure: true) looks up the same non-IP host, the cached servername from the first transport overwrites the current transport's configured value via Object.assign(), causing incorrect SNI and certificate validation against the wrong identity. An authenticated attacker in a multi-tenant deployment can prime the cache with their malicious servername, causing victim transports to connect to attacker-controlled virtual hosts and leak SMTP credentials despite rejectUnauthorized: true.

## Affected products

- Nodemailer Nodemailer 5.0.0 through 10.0.1

## Identifiers

- CVE-2026-100701
- GHSA-6vj9-mwq6-2f5v

## Timeline

- 2026-09-26: disclosed
- 2026-09-26: patched: Fixed in version 10.0.2

## References

- [https://github.com/nodemailer/nodemailer/security/advisories/GHSA-6vj9-mwq6-2f5v](https://github.com/nodemailer/nodemailer/security/advisories/GHSA-6vj9-mwq6-2f5v)
- [https://www.vulncheck.com/advisories/nodemailer-5.0.0-through-10.0.1-tls-servername-cache-confusion](https://www.vulncheck.com/advisories/nodemailer-5.0.0-through-10.0.1-tls-servername-cache-confusion)

## 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)