CVE-2017-18343 in Symfony
Summary
by MITRE
** DISPUTED ** The debug handler in Symfony before v2.7.33, 2.8.x before v2.8.26, 3.x before v3.2.13, and 3.3.x before v3.3.6 has XSS via an array key during exception pretty printing in ExceptionHandler.php, as demonstrated by a /_debugbar/open?op=get URI. NOTE: the vendor's position is that this is not a vulnerability because the debug tools are not intended for production use. NOTE: the Symfony Debug component is used by Laravel Debugbar.
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Analysis
by VulDB Data Team • 08/06/2024
The vulnerability identified as CVE-2017-18343 affects the Symfony framework's debug handler component, specifically targeting versions prior to the mentioned secure releases. This issue manifests as a cross-site scripting vulnerability that occurs during exception pretty printing within the ExceptionHandler.php file, making it particularly concerning for applications that utilize Symfony's debugging capabilities. The vulnerability is triggered when an array key is processed during exception handling, creating a potential attack vector that could be exploited by malicious actors. The specific URI pattern that demonstrates this vulnerability is the /_debugbar/open?op=get endpoint, which serves as the attack surface for the XSS payload execution. This vulnerability exists within Symfony's debug tools that are designed to provide detailed error information and debugging capabilities, but the security implications become significant when these tools are accessible in production environments.
The technical flaw resides in how the Symfony debug handler processes and displays array keys during exception rendering, particularly within the ExceptionHandler.php component. When an exception occurs and the debug handler attempts to pretty print the exception details, it fails to properly sanitize array keys that may contain malicious script content. This improper sanitization creates a classic cross-site scripting vulnerability where an attacker could inject malicious JavaScript code through array keys that are then rendered in the debug output. The vulnerability specifically affects the debug bar functionality that provides detailed information about application exceptions, making it particularly dangerous when debug tools are enabled in production environments where they should not be accessible. The flaw demonstrates a failure in input validation and output sanitization practices, which aligns with CWE-79 - Cross-site Scripting vulnerabilities, and represents a failure in proper data sanitization during debug output generation.
The operational impact of this vulnerability extends beyond the immediate XSS threat, as it demonstrates a broader security misconfiguration issue within web application frameworks. When debug tools are enabled in production environments, they create potential attack surfaces that can be exploited to execute malicious scripts in the context of authenticated users. The vulnerability affects multiple Symfony versions simultaneously, indicating a widespread issue that would require coordinated patching efforts across different release lines. The fact that this vulnerability impacts Laravel Debugbar through its dependency on Symfony's debug component amplifies the potential impact, as it affects a significant portion of the PHP web application ecosystem that relies on these frameworks. This vulnerability highlights the critical importance of properly configuring debug tools and ensuring they are only accessible in development environments, as the security implications of leaving debug functionality enabled in production can be severe.
The vendor's position that this is not a vulnerability because debug tools are not intended for production use represents a common but problematic security stance that can lead to false confidence in application security. This perspective fails to account for the reality that many applications inadvertently leave debug tools accessible in production environments due to misconfiguration or oversight. The vulnerability demonstrates the principle that security should not rely on the assumption that certain features will not be accessible in production, as configuration errors or deployment issues can expose these tools to attackers. Organizations should implement proper access controls and environment-based security configurations to prevent debug tools from being accessible in production environments. The vulnerability also underscores the importance of the principle of least privilege and proper security hardening practices, as the debug functionality should be completely disabled or restricted in production environments according to security best practices and ATT&CK framework considerations for privilege escalation and command execution. The issue highlights the need for comprehensive security testing that includes configuration validation and environment-specific security assessments to prevent such exposure scenarios.