CVE-2024-56527 - Security Vulnerability in TCPDF Before 6.8.: HTML Injection in Error Messages

A security vulnerability has been discovered in the popular PHP library, TCPDF, which is widely used for generating PDF documents. This vulnerability, identified as CVE-2024-56527, affects all versions of TCPDF prior to 6.8.. It could potentially allow malicious users to inject arbitrary HTML and JavaScript code into error messages generated by the library, leading to cross-site scripting (XSS) attacks.

In this post, we will explore the details of this vulnerability, including its background, the affected code snippets, and the possible impacts. Furthermore, links to original references and an overview of exploit possibilities will be provided.

Background

The TCPDF library is an open-source, free-to-use PHP class used for generating PDF documents dynamically. With the capability to manage colors, graphic primitives, and page formatting, it offers tremendous control over the appearance and content of PDFs generated. TCPDF has an active user base and has seen widespread adoption across various web applications.

Original references for this issue were acknowledged in the CHANGELOG.TXT file under version 6.8. in the TCPDF GitHub repository, where this security vulnerability was addressed. You can find it here.

Code Snippet Analysis

The vulnerable code snippet can be found in the Error function, defined in the include/tcpdf_static.php file of the TCPDF library. The problem lies in the missing htmlspecialchars() call for the error message parameter $msg. This allows attackers to inject unescaped content into error messages produced.

Here is the problematic code snippet in the vulnerable versions

public static function Error($msg) {
    // exit with error message
    die('<strong>TCPDF ERROR: </strong>' . $msg);
}

Upon discovering this vulnerability, the necessary patch was applied in version 6.8.. The missing htmlspecialchars() call was added to properly escape the error messages:

public static function Error($msg) {
    // exit with error message
    $msg = htmlspecialchars($msg, ENT_QUOTES, 'UTF-8', false);
    die('<strong>TCPDF ERROR: </strong>' . $msg);
}

Exploit Details

Considering the absence of proper error message escaping in versions earlier than 6.8., an attacker could utilize specially crafted input strings that incorporate HTML or JavaScript code to trigger an error that includes this injected code. By doing so, malicious content can be rendered in the browser, leading to XSS attacks.

A simple example of exploiting this vulnerability could involve making a request to load a non-existent font using the setFont() method, passing in a malformed string that includes HTML or JavaScript code:

$pdf->setFont('<img src=x onerror="alert(1)"></img>');

Upon encountering this error, an unescaped error message containing the injected code would be displayed:

<strong>TCPDF ERROR: </strong>Font file not found: <img src=x onerror="alert(1)"></img>

When rendered in the browser, the HTML and JavaScript code within the error message are executed, compromising the user's session and data.

Conclusion

The security vulnerability CVE-2024-56527 in TCPDF versions earlier than 6.8. could allow attackers to execute cross-site scripting attacks through maliciously injecting code into error messages. Thankfully, this vulnerability was addressed in the 6.8. release, and users are encouraged to update to this version or later to prevent potential exploitation.

As always, it is vital to keep your libraries and packages up-to-date to avoid security issues, as well as to thoroughly scan user-supplied input for possible vulnerabilities.

Timeline

Published on: 12/27/2024 06:15:23 UTC
Last modified on: 03/13/2025 14:15:33 UTC