Nodemailer: RFC 5322 comment inside an angle-bracket address is never stripped

Story map

Why it is Yellow

• CVSS 5.3 medium
• Public exploit or proof of concept referenced
• On your watchlist: npm

Affected packages

References

• https://github.com/advisories/GHSA-g73g-hqqh-jr95
• https://github.com/nodemailer/nodemailer/security/advisories/GHSA-g73g-hqqh-jr95
• https://github.com/nodemailer/nodemailer/commit/a502247555fd81773eac337486781f3b6008e16a
• https://github.com/nodemailer/nodemailer/releases/tag/v10.0.13
• https://github.com/advisories/GHSA-g73g-hqqh-jr95

Original description

## Summary Nodemailer's address parser has three published, patched fixes for RFC 5322 comment `( ... )` handling inside an addr-spec: GHSA-cc9r-2j5m-2m83 (comment glued two domain atoms into one), GHSA-g57g-f23g-4646 (the same glue for a quoted local part), and the related ReDoS fixes GHSA-prgh-xp8r-p3m5 / GHSA-v53p-9fqp-m79j. All three fixes live in `_handleAddress()`'s `joins` / `_recoverAddrSpec()` logic in `src/addressparser/index.ts`, and that logic is exercised whenever the local text-accumulation path in the tokenizer runs. That logic is **never reached at all** for the single most common way a recipient is written: a display name followed by an angle-bracket address, `Name <local@domain>`. When the input inside the angle brackets itself contains an RFC 5322 comment, e.g. ``` Legit User <user@good-corp.com(x)evil.com> ``` the comment is not recognized as an operator, is not stripped, and the parenthesis characters survive **verbatim** inside the parsed address. That value is used as-is for `envelope.to` and is written raw onto the wire in the `RCPT TO` SMTP command. I confirmed this end to end: * against nodemailer's own `jsonTransport`/`streamTransport` (`envelope.to` and the emitted `To:` header both carry the malformed value), and * against a real SMTP server (`aiosmtpd`), where the malformed value is fatal to the transaction (`501 Syntax: RCPT TO: <address> [SP <mail-parameters>]`, all recipients rejected). This reproduces unmodified on every version I tested from `6.9.16` through the current `10.0.12` HEAD, i.e. it predates and survives all three of the address-parser advisories above unchanged, because it is a different root cause in a code path those fixes never touch. ## Root cause ### 1. The tokenizer has a single-slot operator stack `src/addressparser/index.ts`, `Tokenizer.checkChar()`: ```ts } else if (!this.operatorExpecting && !this.inDomainLiteral && chr in this.operators) { this.node = { type: 'operator', value: chr }; this.list.push(this.node); this.node = null; this.operatorExpecting = this.operators[chr]; this.escaped = false; return; } ``` (currently around line 670) `operatorExpecting` is a single string, not a stack. Once `<` opens the address scope, `operatorExpecting` is set to `'>'`. The branch above that recognizes a *new* operator character (such as `(`) is gated on `!this.operatorExpecting`, which is now false. So while inside `<...>`, a `(` is never tokenized as an operator at all — it is just an ordinary character appended to the running text token, together with everything up to the next `>`. The RFC 5322 comment is not recognized, not entered, and not stripped: it rides straight through as literal text. ### 2. The `_handleAddress` state machine loses the `address` state on any operator boundary `src/addressparser/index.ts`, inside `_handleAddress()` (currently around line 365-388): ```ts switch (token.value) { case '<': state = 'address'; insideQuotes = false; break; case '(': state = 'comment'; insideQuotes = false; break; ... default: state = 'text'; insideQuotes = false; break; } ``` Even where a comment *is* recognized (outside angle brackets), closing it with `)` falls through to `default` and resets `state` to `'text'`, not back to whatever state was active before the comment opened. This is why the fixed cases (bare address, quoted local part) only work at all: the leaked comment tail lands in the free-`text` bucket, where `_recoverAddrSpec()`/the ADDR_SPEC extraction logic can find and strip it. Inside `<...>`, none of that applies in the first place (point 1), so there is no text-bucket safety net to fall back on — the whole point 1/point 2 interaction is what makes the angle-bracket case categorically different from, and unprotected by, the three existing fixes. ### 3. The one existing safety net requires whitespace, and this value has none `_recoverAddrSpec()` (currently around line 283) is the function all three prior fixes rely on to peel a clean addr-spec back out of a polluted value. Its very first line is: ```ts function _recoverAddrSpec(data: { address: string; text: string }): void { if (!HAS_WHITESPACE.test(data.address)) { return; } ... ``` `user@good-corp.com(x)evil.com` contains no whitespace at all — the comment content `x` had none, and nothing in the angle-bracket path inserts any — so `_recoverAddrSpec` bails out immediately and never even looks at the value. There is no cleanup path for this shape. ## Proof of Concept Environment: Node.js, current `master` (commit `30e4cfd5902fd5da4d1bc76dc8e4bc92d288adef`, package.json version `10.0.12`), no special transport configuration required. ### Parser-level confirmation ```js const addressparser = require('nodemailer/lib/addressparser'); console.log(addressparser('Legit User <user@good-corp.com(x)evil.com>')); // [ { address: 'user@good-corp.com(x)evil.com', name: 'Legit User' } ] ``` Compare with the already-fixed, unbracketed form of the exact same bytes: ```js console.log(addressparser('user@good-corp.com(x)evil.com')); // [ { address: 'user@good-corp.com', name: 'evil.com' } ] <- correctly stripped ``` ### `sendMail` / envelope confirmation (jsonTransport, no network) ```js const nodemailer = require('nodemailer'); (async () => { const t = nodemailer.createTransport({ jsonTransport: true }); const info = await t.sendMail({ from: 'app@good-corp.com', to: 'Legit User <user@good-corp.com(x)evil.com>', subject: 'hi', text: 'x' }); console.log('envelope.to:', info.envelope.to); })(); ``` Observed output: ``` envelope.to: [ 'user@good-corp.com(x)evil.com' ] ``` The raw `streamTransport` message shows the same value in the emitted header: ``` From: app@good-corp.com To: Legit User <user@good-corp.com(x)evil.com> Subject: hi ``` ### Wire-level confirmation against a real S