GHSA-8C8M-P3M8-CJG8
Vulnerability from github – Published: 2026-10-23 21:53 – Updated: 2026-10-23 21:53Vulnerability 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
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>" }) issues the RCPT TO shown above.
Security impact
Mail intended for an approved recipient is delivered to an attacker chosen domain, disclosing its content, and parsers built on this module report a different author than conformant ones. The misreading only occurs on values a conformant validator approves, so correct validation is bypassed. Affected are applications that pass user influenced addresses to Nodemailer and consumers of the standalone parser such as mailparser.
The fix counts comment depth and ends a comment only at the ) that closes the outermost one.
Found in an internal review of addressparser on 2026-10-18. Verified on 3.0.0, 6.9.16 and 10.1.3.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "nodemailer"
},
"ranges": [
{
"events": [
{
"introduced": "3.0.0"
},
{
"fixed": "10.1.4"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-20",
"CWE-436"
],
"github_reviewed": true,
"github_reviewed_at": "2026-10-23T21:53:04Z",
"nvd_published_at": null,
"severity": "MODERATE"
},
"details": "### Vulnerability summary\n\nRFC 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) \u003cevil@evil.com\u003e) \u003cv@victim.com\u003e` names `v@victim.com` with `x(y) \u003cevil@evil.com\u003e` 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.\n\n### Attacker capabilities\n\nThe 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.\n\n### Realistic exploitation scenario\n\nAn application validates a submitted address with a conformant parser and allows only its own domain. The attacker submits `Victim (x(y) \u003cevil@evil.com\u003e) \u003cv@victim.com\u003e`, 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\u0027s recipient allow list, or the author check of the receiving side.\n\n### Proof of concept\n\n```js\nconst addressparser = require(\u0027nodemailer/lib/addressparser\u0027);\nconsole.log(addressparser(\"Victim (x(y) \u003cevil@evil.com\u003e) \u003cv@victim.com\u003e\"));\n// [ { address: \u0027evil@evil.com\u0027, name: \u0027Victim) v@victim.com\u0027 } ]\n```\n\nPython\u0027s `email._header_value_parser.get_address_list` reads the same value as `v@victim.com` with the display name `Victim`, with no defects reported.\n\nThe envelope a message gets is built from the same parse, so `sendMail({ to: \"Victim (x(y) \u003cevil@evil.com\u003e) \u003cv@victim.com\u003e\" })` issues the RCPT TO shown above.\n\n### Security impact\n\nMail intended for an approved recipient is delivered to an attacker chosen domain, disclosing its content, and parsers built on this module report a different author than conformant ones. The misreading only occurs on values a conformant validator approves, so correct validation is bypassed. Affected are applications that pass user influenced addresses to Nodemailer and consumers of the standalone parser such as mailparser.\n\nThe fix counts comment depth and ends a comment only at the `)` that closes the outermost one.\n\nFound in an internal review of addressparser on 2026-10-18. Verified on 3.0.0, 6.9.16 and 10.1.3.",
"id": "GHSA-8c8m-p3m8-cjg8",
"modified": "2026-10-23T21:53:05Z",
"published": "2026-10-23T21:53:04Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/nodemailer/nodemailer/security/advisories/GHSA-8c8m-p3m8-cjg8"
},
{
"type": "WEB",
"url": "https://github.com/nodemailer/nodemailer/commit/0a8761762ac78f2db2ba37f712f2a52a404ce011"
},
{
"type": "PACKAGE",
"url": "https://github.com/nodemailer/nodemailer"
},
{
"type": "WEB",
"url": "https://github.com/nodemailer/nodemailer/releases/tag/v10.1.4"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N",
"type": "CVSS_V3"
}
],
"summary": "Nodemailer: A nested comment ends early in addressparser, releasing the rest of the comment as a recipient"
}
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