Summary
Nodemailer: A ";" inside a quoted string or comment ends an address group early in addressparser, turning display text into a recipient
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; <[email protected]>) <[email protected]>; names only [email protected], and Nodemailer read it as the single recipient [email protected]. 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.
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; <[email protected]>) <[email protected]>;. The validator sees one mailbox, [email protected], and approves it. Nodemailer delivers to [email protected] only. The same works through a quoted display name, G: "a;" "<[email protected]>" <[email protected]>;. The boundary crossed is the application's recipient allow list.
Proof of concept
const addressparser = require('nodemailer/lib/addressparser');
console.log(addressparser("G: (a; <[email protected]>) <[email protected]>;"));
// [ { name: 'G', group: [ [Object] ] }, { address: '[email protected]', name: ') [email protected]' } ]
Python's email._header_value_parser.get_address_list reads the same value as the single mailbox [email protected], with no defects reported.
The envelope a message gets is built from the same parse, so sendMail({ to: "G: (a; <[email protected]>) <[email protected]>;" }) 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.
Impact
The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths. Typical impact: varies by context: data corruption, logic bypass, or denial of service.
GHSA-M943-M63M-W62W has a CVSS score of 6.5 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (10.1.4); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Frequently Asked Questions
- What is GHSA-M943-M63M-W62W? GHSA-M943-M63M-W62W is a medium-severity improper input validation vulnerability in nodemailer (npm), affecting versions >= 3.0.0, < 10.1.4. It is fixed in 10.1.4. The application does not adequately validate input before processing it, allowing unexpected values to reach sensitive code paths.
- How severe is GHSA-M943-M63M-W62W? GHSA-M943-M63M-W62W has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of nodemailer are affected by GHSA-M943-M63M-W62W? nodemailer (npm) versions >= 3.0.0, < 10.1.4 is affected.
- Is there a fix for GHSA-M943-M63M-W62W? Yes. GHSA-M943-M63M-W62W is fixed in 10.1.4. Upgrade to this version or later.
- Is GHSA-M943-M63M-W62W exploitable, and should I be worried? Whether GHSA-M943-M63M-W62W is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether GHSA-M943-M63M-W62W is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix GHSA-M943-M63M-W62W? Upgrade
nodemailerto 10.1.4 or later.