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.
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: <img src=xyz onerror=alert(1)>.
PoC
Resulting output file (emailText.html):
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
mailgen
<= 2.0.30
2.0.31
Связанные уязвимости
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.