GHSA-268h-hp4c-crq3 Nodemailer: CRLF injection in Nodemailer List-* header comments allows arbitrary message header injection
SummaryNodemailer constructs `List-*` headers from the caller-provided `list` message option using internally prepared header values. The `list.*.comment` field is inserted into those prepared values without removing CR (`\r`) or LF (`\n`) characters. Because prepared headers bypass the normal header-value sanitizer and are passed to `mimeFuncs.foldLines()`, a CRLF sequence in a list comment is emitted as an actual header boundary in the generated RFC822 message.An application that lets a lower-privileged or unauthenticated user influence `list.help.comment`, `list.unsubscribe.comment`, `list.subscribe.comment`, `list.post.comment`, `list.owner.comment`, `list.archive.comment`, or `list.id.comment` can therefore be made to generate messages containing attacker-chosen additional headers.DetailsSource-to-sink evidence:`lib/mailer/mail-message.js:241-249` calls `_getListHeaders(this.data.list)` and adds each returned value with `this.message.addHeader(listHeader.key, value)`.`lib/mailer/mail-message.js:253-296` builds each list header value as `{ prepared: true, foldLines: true, value: ... }`.For `List-ID`, `lib/mailer/mail-message.js:272-279` copies `value.comment` into the generated header value. If `mimeFuncs.isPlainText(comment)` returns true, it wraps the comment in quotes rather than encoding or CRLF-normalizing it.For the other `List-*` headers, `lib/mailer/mail-message.js:283-288` copies `value.comment` into `(<comment>)`. If `mimeFuncs.isPlainText(comment)` returns true, the value is not encoded or CRLF-normalized.`lib/mime-node/index.js:323-351` accepts the prepared header object.`lib/mime-node/index.js:533-540` trusts `options.prepared`; when `foldLines` is set, it pushes `mimeFuncs.foldLines(key + ': ' + value)` directly into the header block.The normal header-value sanitizer path is bypassed because the value is marked prepared. By contrast, ordinary unprepared header values are normalized in the regular header-building path.`lib/mailer/mail-message.js:299-308` removes whitespace and angle brackets from `list.*.url`, so the confirmed injection source is the `comment` field, not the URL field.Default/common exposure evidence:`lib/nodemailer.js:21-60` exposes the public `createTransport(...).sendMail(...)` flow used by the package.`examples/full.js:106-123` documents `list.unsubscribe.comment` and `list.id.comment` as normal message options.The behavior is in shipped runtime code and does not require test-only code, non-default build steps, or undocumented internals.False-positive screening and negative controls:SMTP command construction was separately reviewed. Envelope sender/recipients reject CRLF before SMTP commands, EHLO names strip CRLF, SIZE is numeric, and DSN fields are encoded; no SMTP command-injection variant was confirmed.Ordinary `subject` header input containing CRLF was normalized to a single `Subject:` header and did not create `X-Injected` in the local control case.Address display names and MIME filename/content-type parameters were reviewed by a focused MIME/header audit and were encoded or CRLF-normalized in local checks.`prepared: true` custom headers are an explicit low-level escape hatch, but this issue is different because Nodemailer itself creates prepared headers from the documented `list.*.comment` option.Variant analysis:Local testing confirmed the same root cause for comments in `List-Help`, `List-Unsubscribe`, `List-Subscribe`, `List-Post`, `List-Owner`, `List-Archive`, and `List-ID`. These should be fixed together by rejecting or normalizing CR/LF in list comments before prepared header generation, or by avoiding the prepared-header bypass for caller-controlled list values.Affected version evidence and uncertainty:Confirmed vulnerable: `nodemailer` 8.0.8 at commit `15138a84c543c20aa399218534cdbbfa2ea1ce55`.Git history shows `_getListHeaders` present in historical commits including `22fcff8` (`v4.3.0`) and related list-header work in `9b4f90a` (`v3.1.8`), but older versions were not dynamically tested during this audit.Affected range is therefore recorded as unknown beyond the confirmed current version.No patched version was identified in this checkout.Severity rationale:AV: The vulnerable library path is reached through application-level message submission in typical networked applications that use Nodemailer.AC: A single CRLF sequence in a documented message option triggers the issue.PR: Conservative assumption that the attacker is a lower-privileged user of an application that exposes list metadata fields. Some applications could expose this to unauthenticated users, but that was not assumed.UI: No maintainer or victim interaction is needed after the application accepts the message object.S: The impact remains in the application/mail-generation security scope.C/I: Injected headers can affect message metadata, mail-client/filter interpretation, and downstream mail-pipeline decisions. No SMTP envelope recipient injection or code execution was demonstrated.A: No availability impact was demonstrated.Final self-review:Reproduction evidence was generated locally from this checkout with a safe in-memory `streamTransport` PoC and a negative `Subject` control case.The PoC is non-destructive and does not send network traffic outside the process.The observed output contains an actual CRLF-delimited injected header line.Reachability, sanitizer bypass, package exposure, variants, and non-exploitable sibling paths were checked as described above.The affected range is not overclaimed; only the current tested version is confirmed vulnerable.PoCFrom a clean checkout of `nodemailer` at commit `15138a84c543c20aa399218534cdbbfa2ea1ce55`, run:Observed output in this environment:Expected vulnerable output: `POSITIVE_HAS_INJECTED=true` and all listed variants ending in `=true`. Expected negative/control output: `CONTROL_HAS_INJECTED=false`, showing the ordinary `Subject` header path does not create a separate injected header.Cleanup: none required; the PoC uses only in-memory message generation.ImpactA lower-privileged attacker who can influence `list.*.comment` fields in an application using Nodemailer can inject arbitrary additional headers into generated email messages. This can alter message semantics and downstream mail-client or mail-filter behavior, including adding attacker-controlled metadata headers. The PoC confirms header-boundary injection in the generated RFC822 output; it does not demonstrate SMTP command injection, recipient injection, or code execution.Suggested remediationNormalize or reject CR and LF in `list.*.comment` before constructing prepared `List-*` headers. Prefer sharing the same CRLF-neutralization behavior used for ordinary header values, or avoid using `prepared: true` for caller-controlled list comment content. Add regression tests for CRLF in every documented `list` comment-bearing field and verify that generated messages do not contain attacker-controlled standalone headers.
CVSS v3.1 score: 5.4