GHSA-8c8m-p3m8-cjg8 - Nodemailer: A nested comment ends early in addressparser, releasing the rest of the comment as a recipient
### Vulnerability summary
RFC 5322 comments nest. addressparser ended a comment at the first `)`, including the one that closes a nested comment, and parsed the rest of the outer comment as header text. `Victim (x(y) <evil@evil.com>) <v@victim.com>` names `v@victim.com` with `x(y) <evil@evil.com>` as a comment, and Nodemailer read it as the address `evil@evil.com`. This is the same shape as the escaped parenthesis fixed in 10.1.2, reached through nesting instead of a quoted-pair. Affected: 3.0.0 through 10.1.3.
### Attacker capabilities
The attacker controls the text of an address that an application passes to Nodemailer, or the From or To header of an inbound message parsed with mailparser. No access to the application, its configuration or its credentials is needed. The value is a syntactically valid RFC 5322 address that conformant parsers accept without defects.
### Realistic exploitation scenario
An application validates a submitted address with a conformant parser and allows only its own domain. The attacker submits `Victim (x(y) <evil@evil.com>) <v@victim.com>`, which validates as `v@victim.com`. Nodemailer delivers to `evil@evil.com`. In the inbound direction, a DMARC or display layer built on a conformant parser and a mail client built on mailparser disagree on the author of the same message, which is the setting for sender spoofing. The boundary crossed is the application's recipient allow list, or the author check of the receiving side.
### Proof of concept
```js
const addressparser = require('nodemailer/lib/addressparser');
console.log(addressparser("Victim (x(y) <evil@evil.com>) <v@victim.com>"));
// [ { address: 'evil@evil.com', name: 'Victim) v@victim.com' } ]
```
Python's `email._header_value_parser.get_address_list` reads the same value as `v@victim.com` with the display name `Victim`, with no defects reported.
The envelope a message gets is built from the same parse, so `sendMail({ to: "Victim (x(y) <evil@evil.com>) <v@victim.com>" })` iss
MEDIUM
Severity & confidence
Source severitymedium
Platform severitymedium
Confidencemedium
Exploitationunknown
CVSS6.5
Affected
Vendorsnodemailer
Productsnodemailer
Reporting sources (1)
GitHub Security Advisories
Timeline & provenance
Published2026-10-23T21:53:04
Last updated2026-10-27T18:57:28
Ingested2026-10-23T22:03:29
FreshnessNEAR-REAL-TIME
Threat typeadvisory
Recommended action
Review the advisory and upgrade affected packages to the first patched version.
Next steps
- Identify affected systems in your environment.
- Apply the vendor patch or mitigation guidance.
- Review logs for indicators described in the advisory.
- Follow the affected vendor/product to track updates.
Confidence explanation
Reported by a single or secondary source; treat as indicative, verify before acting.
Source type: vendor ยท Original: GitHub Security Advisories