# CVE-2026-100701: Nodemailer 5.0.0 through 10.0.1 TLS servername Cache Confusion

> An attacker can exploit a DNS cache flaw in Nodemailer to force incorrect TLS servername validation, potentially disclosing SMTP credentials in multi-tenant environments.

- **Severity:** Medium 6.0 (`CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:H/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 26 Sep 2026
- **Updated:** 26 Sep 2026
- **Also known as:** CLEANSTART-2026-HG25385, CLEANSTART-2026-HM32228, CLEANSTART-2026-RE54835, CLSA-2026-1790673224, CLSA-2026-1790676821, CLSA-2026-1792139197, CLSA-2026-1792429268, DEBIAN-CVE-2026-100701, ECHO-94cb-1303-48fb, GHSA-2mg4-38wg-2h6f, GHSA-6vj9-mwq6-2f5v, MINI-382w-fxj2-c42r, MINI-3m96-xh7r-w5mw, MINI-3xp6-vqgw-hxxf, MINI-6j7g-xhmp-v9pg, MINI-87cc-fwgm-2f6r, MINI-9g8f-c762-82gg, MINI-c9q6-mghv-5qj2, MINI-cc3c-vw9w-wqxm, MINI-cr44-5jmg-7r3g, MINI-f96p-m8xh-5p7r, MINI-jhm3-78jc-mrp3, MINI-p3rg-pc2r-w9mw, MINI-p56m-38g3-4p29, MINI-r25p-5wqv-qmvj, MINI-wg54-j58f-wxqf, UBUNTU-CVE-2026-100701

## What is CVE-2026-100701?

CVE-2026-100701 is a medium-severity vulnerability in nodemailer, published on 26 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Nodemailer versions 5.0.0 through 10.0.1 use a process-global DNS cache that is keyed only by the DNS host, while each cache entry also stores the caller-specific TLS servername. When two direct TLS/SMTPS transports (secure: true) resolve the same non-IP host with different tls.servername values, the first transport's servername is returned on the cache hit and overwrites the second transport's explicitly configured value, so Nodemailer sends the wrong SNI value and validates the peer certificate against the wrong identity. In multi-tenant services or SNI-routed SMTP gateways, an attacker who can prime the cache can cause a victim transport to connect to the attacker's TLS virtual host and accept the attacker's certificate even with rejectUnauthorized: true, disclosing the victim's SMTP credentials. Fixed in 10.0.2.

Weakness: CWE-295 (Improper Certificate Validation)

## Which versions are affected by CVE-2026-100701?

2 open source packages ship an affected version, including nodemailer.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `nodemailer` | npm | From 5.0.0 | 10.0.2 |
| `nodemailer` | npm | From 5.0.0 | 10.0.2 |

## How do I fix CVE-2026-100701?

Upgrade nodemailer to 10.0.2 or later.

## Is CVE-2026-100701 being exploited?

There is no known exploitation of CVE-2026-100701 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-100701 and fix it if it is affected.

What it is: CVE-2026-100701 is a medium-severity vulnerability in nodemailer, published on 26 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-100701 in the wild and no public exploit code.

Affected packages and fixed versions:
- nodemailer (npm): affected from 5.0.0; fixed in 10.0.2
- nodemailer (npm): affected from 5.0.0; fixed in 10.0.2

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-100701/ (Markdown: https://insights.sbomify.com/CVE-2026-100701/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-100701
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-100701
- OSV: https://osv.dev/vulnerability/CVE-2026-100701

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-100701/
Summaries are generated and may contain mistakes; the official description above is the record.