GHSA-8m3c-c648-2xjj

Nodemailer: resolveContent() on a MailMessage bypasses disableFileAccess/disableUrlAccess when called with the legacy signature

Published

2026-09-08

Modified

2026-09-08

Sources

github-advisory

Summary

### Summary Nodemailer's `disableFileAccess` / `disableUrlAccess` options are a security sandbox that lets an application forbid untrusted message content (`html`/`text`/attachment `path`/`href`) from reading local files or making outbound HTTP(S) requests. The fix for GHSA-wqvq-jvpq-h66f (commit `5f69497`) threaded these flags through the library's internal resolution paths (`MailMessage.resolveAll()` and `_convertDataImages()`), but the public plugin API `MailMessage.resolveContent(...args)` (`lib/mailer/mail-message.js:41-43`) remains a raw passthrough to `shared.resolveContent()`. When called with the documented legacy signature `mail.resolveContent(data, key, callback)`, `shared.resolveContent` normalizes the missing options argument to an empty object (`options = options || {}`, `lib/shared/index.js:530`). The message-level flags that the `MailMessage` constructor already copied into `mail.data` (`lib/mailer/mail-message.js:34-38`) are silently discarded, so `resolveContentValue` skips both access-control guards and reaches `nmfetch(url)` (SSRF, `lib/shared/index.js:588`) or `fs.createReadStream(path)` (arbitrary file read, `lib/shared/index.js:597`). A plugin or application code that resolves message content through the documented API (the same API the library's own `_convertDataImages` uses, threading the flags explicitly) thereby bypasses the sandbox an application deliberately enabled. ### Details Root cause. The `MailMessage` constructor stores the transporter-level sandbox flags on the message object (`lib/mailer/mail-message.js:34-38`): ```js ['disableFileAccess', 'disableUrlAccess', 'normalizeHeaderKey', 'maxRecipients'].forEach(key => { if (key in options) { this.data[key] = options[key]; } }); ``` The public resolver is a pure passthrough (`lib/mailer/mail-message.js:41-43`): ```js resolveContent(...args) { return shared.resolveContent(...args); } ``` `shared.resolveContent` supports the legacy 3-argument signature and collapses the missing options to `{}` (`lib/shared/index.js:524-530`): ```js module.exports.resolveContent = (data, key, options, callback) => { // options is optional; support the legacy resolveContent(data, key, callback) signature if (!callback && typeof options === 'function') { callback = options; options = false; } options = options || {}; ... resolveContentValue(data, key, options, callback); ``` `resolveContentValue` then checks `options.disableUrlAccess` / `options.disableFileAccess` (`lib/shared/index.js:581` / `:590`), both `undefined` for the legacy signature, so it falls through to `nmfetch` (`:588`) or `fs.createReadStream` (`:597`). Contrast with the fixed paths. `resolveAll()` (`lib/mailer/mail-message.js:112-115`) and `_convertDataImages()` (`lib/mailer/index.js:437-440`) both pass the message flags explicitly. The MIME streaming path (`lib/mime-node/index.js:1059-1077`) also honors the flags. So an application that enables the sandbox and then calls `transporter.sendMail()` is protected; the bypass appears only when message content is resolved through the public legacy-signature API — which is the documented plugin usage (the `resolveContent` JSDoc at `lib/shared/index.js:510-523` states it is "useful when you want to create a plugin that needs a content value"). Affected versions. Confirmed on `9.1.0` (HEAD `efd6e29c10c6e0c25c57bd2f2a71302838235a4f`, the current npm latest). The gap was introduced by the GHSA-wqvq-jvpq-h66f fix and is still present; the public API has no regression coverage (`test/mailer/mail-message-test.js` contains no `resolveContent` test). ### PoC Requires: `[email protected]`, a readable local file, and any reachable HTTP endpoint (loopback suffices). Non-destructive; no network egress beyond a local listener. ```js 'use strict'; const nodemailer = require('nodemailer'); const MailMessage = require('nodemailer/lib/mailer/mail-message'); const TARGET_FILE = '/app/src/package.json';

Affected packages

Remediation: Upgrade to 9.1.1 or later.

References

• https://github.com/advisories/GHSA-8m3c-c648-2xjj