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Response snapshot Oct 26, 2026, 22:12 UTC

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VulnerabilityGHSA-m943-m63m-w62w

Nodemailer: A ";" inside a quoted string or comment ends an address group early in addressparser, turning display text into a recipient

addressparser ends an RFC 5322 group at the first `;`, including one inside a quoted display name or a comment. The text after it is parsed again as top level recipients with the quoting flipped, so text that every conformant parser reads as a display name or comment becomes a live address.

Published Updated

At a glance

Exploited
Not known
Severity
Not scored yet
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: nodemailer: 10.1.4. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-m943-m63m-w62w (opens a new tab)

What happened

### Vulnerability summary

addressparser ends an RFC 5322 group at the first `;`, including one inside a quoted display name or a comment. The text after it is parsed again as top level recipients with the quoting flipped, so text that every conformant parser reads as a display name or comment becomes a live address. `G: (a; ) ;` names only `v@victim.com`, and Nodemailer read it as the single recipient `evil@evil.com`. Affected: 3.0.0 through 10.1.3.

### Attacker capabilities

The attacker controls the text of an address field that an application passes to Nodemailer, or the 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 group that conformant parsers accept without defects.

Continue reading

### Realistic exploitation scenario

An application validates the recipients of a submitted address list with a conformant parser and only allows addresses at its own domain. The attacker submits `G: (a; ) ;`. The validator sees one mailbox, `v@victim.com`, and approves it. Nodemailer delivers to `evil@evil.com` only. The same works through a quoted display name, `G: "a;" " " ;`. The boundary crossed is the application's recipient allow list.

### Proof of concept

```js const addressparser = require('nodemailer/lib/addressparser'); console.log(addressparser("G: (a; ) ;")); // [ { name: 'G', group: [ [Object] ] }, { address: 'evil@evil.com', name: ') v@victim.com' } ] ```

Python's `email._header_value_parser.get_address_list` reads the same value as the single mailbox `v@victim.com`, with no defects reported.

The envelope a message gets is built from the same parse, so `sendMail({ to: "G: (a; ) ;" })` issues the RCPT TO shown above.

### Security impact

Mail that an application intends for an approved recipient goes to a recipient chosen by the attacker, which discloses its content, and the intended recipient never receives it. The misreading only occurs on values a conformant validator approves, so correct validation is bypassed, which makes it a security issue rather than a parsing bug. Affected are applications that pass user influenced address lists to Nodemailer and consumers of the standalone parser such as mailparser.

The fix tracks quoted strings and comments inside a group and reads only a `;` outside them.

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 ranges reported by GitHub: nodemailer: >= 3.0.0, < 10.1.4

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-m943-m63m-w62w (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-m943-m63m-w62w, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 23). Nodemailer: A ";" inside a quoted string or comment ends an address group early in addressparser, turning display text into a recipient. https://kevwire.com/record/GHSA-m943-m63m-w62w

MLA

"Nodemailer: A ";" inside a quoted string or comment ends an address group early in addressparser, turning display text into a recipient." KEVWire, 23 Oct. 2026, kevwire.com/record/GHSA-m943-m63m-w62w.

Chicago

KEVWire. "Nodemailer: A ";" inside a quoted string or comment ends an address group early in addressparser, turning display text into a recipient." Last modified October 23, 2026. https://kevwire.com/record/GHSA-m943-m63m-w62w.

Evidence summary (plain text)

Nodemailer: A ";" inside a quoted string or comment ends an address group early in addressparser, turning display text into a recipient (Oct 23, 2026).
addressparser ends an RFC 5322 group at the first `;`, including one inside a quoted display name or a comment. The text after it is parsed again as top level recipients with the quoting flipped, so text that every conformant parser reads as a display name or comment becomes a live address. `G: (a; ) ;` names only `v@victim.com`, and Nodemailer read it as the single recipient `evil@evil.com`. Affected: 3.0.0 through 10.1.3.

The attacker controls the text of an address field that an application passes to Nodemailer, or the 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 group that conformant parsers accept without defects.
Sources:
GitHub-reviewed advisory GHSA-m943-m63m-w62w: https://github.com/advisories/GHSA-m943-m63m-w62w
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: GHSA-m943-m63m-w62w.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 26, 2026, 20:55 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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