Header Injection in Symfony MIME Component

Executive Summary

This vulnerability is a CRLF injection flaw in Symfony's Mime component. It occurs in the ParameterizedHeader class which handles email headers like Content-Type or Content-Disposition. The issue allows attackers to inject malicious parameter names containing non-token characters such as CRLF sequences, enabling them to terminate existing headers and add new ones. This happens because the class validates and encodes parameter values but not parameter names, which are emitted verbatim.

Useful 0 Not Useful 0

Detection Guidance

Detecting this vulnerability requires checking if your system is running an affected version of Symfony. The vulnerability affects Symfony versions prior to 5.4.52, 6.4.40, 7.4.12, and 8.0.12.

• Check the installed version of Symfony using Composer. Run the following command in your project directory: composer show symfony/symfony or composer show symfony/mime. Compare the output with the affected version ranges.
• Inspect your application's dependencies to identify if any vulnerable versions of symfony/mime or symfony/symfony are present. Use: composer audit or composer why symfony/mime.
• Review your application's code for instances where the ParameterizedHeader class is used, particularly in email header construction. Look for direct or indirect usage of untrusted input in parameter names for headers like Content-Type or Content-Disposition.

Network-level detection is challenging since this is a code-level vulnerability. However, you can monitor outgoing emails for unusual headers or malformed MIME structures that might indicate exploitation attempts.

Useful 0 Not Useful 0

Impact Analysis

If exploited, this vulnerability could allow attackers to manipulate email headers, potentially leading to phishing attacks, spoofing legitimate emails, or bypassing security measures. Attackers might inject malicious headers to alter email content, redirect recipients to fraudulent sites, or exfiltrate sensitive data through crafted emails.

Useful 0 Not Useful 0

Compliance Impact

This vulnerability could impact compliance by enabling unauthorized data access or manipulation through email header injection. For GDPR, it may lead to breaches of confidentiality or integrity of personal data. For HIPAA, it could compromise protected health information integrity. Organizations using vulnerable Symfony versions risk non-compliance due to inadequate security controls.

Useful 0 Not Useful 0

Mitigation Strategies

The primary mitigation step is to upgrade Symfony to a patched version. The vulnerability is fixed in versions 5.4.52, 6.4.40, 7.4.12, and 8.0.12.

• Update the symfony/mime or symfony/symfony package using Composer. Run: composer require symfony/mime:^5.4.52 or the appropriate version for your project (e.g., ^6.4.40, ^7.4.12, or ^8.0.12).
• If upgrading is not immediately possible, apply a temporary workaround by validating all parameter names used in email headers manually. Ensure they conform to RFC 2045 and RFC 5322 token standards, rejecting any names containing non-token characters (e.g., spaces, semicolons, equals signs, quotes, or control characters like CRLF).
• Review and sanitize all untrusted input used in constructing email headers, particularly parameter names for headers like Content-Type or Content-Disposition. Avoid deriving parameter names directly from user input.
• Monitor your application for any signs of exploitation, such as malformed email headers or unexpected behavior in email sending functionality.

Useful 0 Not Useful 0