CVE-2026-92595

Nodemailer (npm package nodemailer) versions 9.1.0 and earlier do not honor the disableFileAccess and disableUrlAccess sandbox options when message content is resolved through the public plugin API MailMessage.resolveContent() using the documented legacy three-argument signature resolveContent(data, key, callback). Because shared.resolveContent() normalizes the missing options argument to an empty object, the message-level flags copied into mail.data by the MailMessage constructor are discarded, and resolveContentValue() skips both access-control checks, reaching nmfetch(url) or fs.createReadStream(path). As a result, plugin or application code that resolves untrusted message content (html, text, attachment path or href) via this API can be induced to read arbitrary local files or issue outbound HTTP(S) requests (server-side request forgery), bypassing the sandbox the application enabled. The internal paths used by transporter.sendMail() (resolveAll(), _convertDataImages(), and the MIME streaming path) are not affected. Fixed in version 9.1.1.

Nodemailer (npm package nodemailer) versions 9.1.0 and earlier do not honor the disableFileAccess and disableUrlAccess sandbox options when message content is resolved through the public plugin API MailMessage.resolveContent() using the documented legacy three-argument signature resolveContent(data, key, callback). Because shared.resolveContent() normalizes the missing options argument to an empty object, the message-level flags copied into mail.data by the MailMessage constructor are discarded, and resolveContentValue() skips both access-control checks, reaching nmfetch(url) or fs.createReadStream(path). As a result, plugin or application code that resolves untrusted message content (html, text, attachment path or href) via this API can be induced to read arbitrary local files or issue outbound HTTP(S) requests (server-side request forgery), bypassing the sandbox the application enabled. The internal paths used by transporter.sendMail() (resolveAll(), _convertDataImages(), and the MIME streaming path) are not affected. Fixed in version 9.1.1.

Nodemailer (npm package nodemailer) versions 9.1.0 and earlier do not honor the disableFileAccess and disableUrlAccess sandbox options when message content is resolved through the public plugin API MailMessage.resolveContent() using the documented legacy three-argument signature resolveContent(data, key, callback). Because shared.resolveContent() normalizes the missing options argument to an empty object, the message-level flags copied into mail.data by the MailMessage constructor are discarded, and resolveContentValue() skips both access-control checks, reaching nmfetch(url) or fs.createReadStream(path). As a result, plugin or application code that resolves untrusted message content (html, text, attachment path or href) via this API can be induced to read arbitrary local files or issue outbound HTTP(S) requests (server-side request forgery), bypassing the sandbox the application enabled. The internal paths used by transporter.sendMail() (resolveAll(), _convertDataImages(), and the MIME streaming path) are not affected. Fixed in version 9.1.1.

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):

['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: [email protected], 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 =…

Nodemailer (npm package nodemailer) versions 9.1.0 and earlier do not honor the disableFileAccess and disableUrlAccess sandbox options when message content is resolved through the public plugin API MailMessage.resolveContent() using the documented legacy three-argument signature resolveContent(data, key, callback). Because shared.resolveContent() normalizes the missing options argument to an empty object, the message-level flags copied into mail.data by the MailMessage constructor are discarded, and resolveContentValue() skips both access-control checks, reaching nmfetch(url) or fs.createReadStream(path). As a result, plugin or application code that resolves untrusted message content (html, text, attachment path or href) via this API can be induced to read arbitrary local files or issue outbound HTTP(S) requests (server-side request forgery), bypassing the sandbox the application enabled. The internal paths used by transporter.sendMail() (resolveAll(), _convertDataImages(), and the MIME streaming path) are not affected. Fixed in version 9.1.1.

Nodemailer (npm package nodemailer) versions 9.1.0 and earlier do not honor the disableFileAccess and disableUrlAccess sandbox options when message content is resolved through the public plugin API MailMessage.resolveContent() using the documented legacy three-argument signature resolveContent(data, key, callback). Because shared.resolveContent() normalizes the missing options argument to an empty object, the message-level flags copied into mail.data by the MailMessage constructor are discarded, and resolveContentValue() skips both access-control checks, reaching nmfetch(url) or fs.createReadStream(path). As a result, plugin or application code that resolves untrusted message content (html, text, attachment path or href) via this API can be induced to read arbitrary local files or issue outbound HTTP(S) requests (server-side request forgery), bypassing the sandbox the application enabled. The internal paths used by transporter.sendMail() (resolveAll(), _convertDataImages(), and the MIME streaming path) are not affected. Fixed in version 9.1.1.