Executive Summary

[{'type': 'paragraph', 'content': "CVE-2026-3455 is a Cross-site Scripting (XSS) vulnerability in the mailparser npm package versions before 3.9.3. It occurs in the textToHtml() function, which improperly sanitizes URLs in email content. Attackers can inject malicious JavaScript by adding extra quotation marks to URLs, causing the generated HTML anchor tags to break out of their attribute context and execute arbitrary scripts in the victim's browser."}, {'type': 'paragraph', 'content': 'Specifically, the vulnerability arises because URLs and link text are inserted directly into the href attribute and link text without proper escaping or encoding. For example, a malicious URL like http://google.com?"onmouseover="alert(\'XSS\')" results in an anchor tag that executes JavaScript when a user interacts with it.'}, {'type': 'paragraph', 'content': 'This vulnerability allows attackers to bypass the Same Origin Policy and execute scripts in the context of trusted websites, potentially leading to cookie theft, session hijacking, and other malicious actions.'}] [1, 2, 4]

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Impact Analysis

This vulnerability can impact you by allowing attackers to execute arbitrary JavaScript code in your browser when you process malicious emails using the affected mailparser versions. This can lead to several security risks including:

• Stealing cookies and session tokens, which can lead to account hijacking.
• Exposing sensitive information displayed or accessible in the browser.
• Hijacking user sessions and impersonating users.
• Accessing privileged services or performing unauthorized actions.
• Delivering malware or further malicious payloads through the browser.

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Compliance Impact

I don't know

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Detection Guidance

[{'type': 'paragraph', 'content': 'This vulnerability can be detected by analyzing email content processed by the mailparser package, specifically looking for malicious URLs containing extra double quotes that break out of HTML attributes and inject JavaScript code.'}, {'type': 'paragraph', 'content': "A practical detection method involves parsing suspicious emails with a test script using the mailparser library's simpleParser function to generate HTML output and then inspecting the output for injected event handlers or script tags."}, {'type': 'paragraph', 'content': 'For example, a proof-of-concept test script can parse a crafted .eml email file containing a malicious URL like `http://google.com?"onmouseover="alert(\'XSS\')"` and write the vulnerable HTML output to a file (e.g., poc_output.html). Opening this file in a browser will trigger the XSS alert if the vulnerability is present.'}, {'type': 'paragraph', 'content': 'No specific network commands are provided in the resources, but monitoring email processing logs and scanning for suspicious URLs with embedded quotes in email content processed by mailparser can help detect exploitation attempts.'}] [2]

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Mitigation Strategies

The primary and immediate mitigation step is to upgrade the mailparser package to version 3.9.3 or later, where the vulnerability has been fixed.

The fix involves escaping double quotes in URLs before inserting them into HTML anchor tags and HTML-encoding the link text to prevent injection of malicious scripts.

• Upgrade mailparser to version 3.9.3 or later.
• Sanitize and validate all user inputs, especially URLs extracted from emails.
• Escape special characters in URLs and link text before embedding them into HTML.
• Implement Content Security Policies (CSP) to restrict execution of unauthorized scripts.
• Disable client-side scripts where possible to reduce attack surface.
• Redirect or block invalid requests containing suspicious URL patterns.
• Detect and invalidate simultaneous logins to reduce session hijacking risks.

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