CVE-2024-50340: Symfony Runtime RCE Vulnerability

CVE-2024-50340 Overview

CVE-2024-50340 is an injection vulnerability (CWE-74) in the symfony/runtime module for the Symfony PHP framework. This component is designed to decouple PHP applications from global state. When the register_argv_argc PHP directive is set to on, attackers can exploit specially crafted query strings to manipulate the environment or debug mode used by the kernel when handling requests. This can lead to unauthorized information disclosure, application state manipulation, and potential security bypasses.

Critical Impact

Attackers can remotely manipulate the application environment and debug settings through crafted URL query strings, potentially exposing sensitive debugging information and altering application behavior without authentication.

Affected Products

• Symfony Runtime versions prior to 5.4.46
• Symfony Runtime versions 6.x prior to 6.4.14
• Symfony Runtime versions 7.x prior to 7.1.7

Discovery Timeline

• 2024-11-06 - CVE-2024-50340 published to NVD
• 2024-11-08 - Last updated in NVD database

Technical Details for CVE-2024-50340

Vulnerability Analysis

This vulnerability stems from improper input validation in the SymfonyRuntime class. When PHP's register_argv_argc directive is enabled, the runtime incorrectly processes $_SERVER['argv'] values from web requests, allowing attackers to inject environment configuration parameters through URL query strings. This behavior was unintended for non-CLI (SAPI) PHP runtimes and enables remote attackers to modify critical application settings such as the environment mode (e.g., switching from production to debug) without any authentication requirements.

The attack can be executed remotely over the network with low complexity, requiring no privileges or user interaction. A successful exploit can result in low-level impacts to confidentiality, integrity, and availability of the application.

Root Cause

The root cause is an improper separation between CLI and web (SAPI) execution contexts in the SymfonyRuntime class. The vulnerable code path reads from $_SERVER['argv'] when processing environment options, even in web request contexts where argv values can be manipulated via URL query parameters. This behavior violates the principle of least privilege by allowing web users to access functionality intended only for command-line execution.

Attack Vector

The attack vector is network-based and requires the following conditions:

1. The target Symfony application uses the vulnerable symfony/runtime component
2. PHP's register_argv_argc directive is set to on
3. The attacker crafts a malicious query string that injects environment or debug parameters

Attackers can exploit this by sending HTTP requests with specially crafted query strings that populate $_SERVER['argv'] with malicious values. When the SymfonyRuntime processes these values, it applies the attacker-controlled environment settings to the kernel, potentially enabling debug mode or switching the application environment.

// Security patch in src/Symfony/Component/Runtime/SymfonyRuntime.php
// Source: https://github.com/symfony/symfony/commit/a77b308c3f179ed7c8a8bc295f82b2d6ee3493fa
 
         if (isset($options['env'])) {
             $_SERVER[$envKey] = $options['env'];
-        } elseif (isset($_SERVER['argv']) && class_exists(ArgvInput::class)) {
+        } elseif (empty($_GET) && isset($_SERVER['argv']) && class_exists(ArgvInput::class)) {
             $this->options = $options;
             $this->getInput();
         }

The patch adds a check for empty($_GET) to ensure that $_SERVER['argv'] is only processed when no GET parameters are present, effectively blocking web-based exploitation while preserving CLI functionality.

Detection Methods for CVE-2024-50340

Indicators of Compromise

• Unusual HTTP requests containing environment-related query parameters such as --env=, --debug, or APP_ENV=
• Web server logs showing requests with CLI-style arguments in query strings
• Unexpected application behavior indicating environment or debug mode changes
• Application logs showing production applications running in debug mode without administrative action

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block query strings containing CLI-style arguments like --env or --debug
• Monitor application logs for environment mode changes that don't correlate with deployment activities
• Use runtime application self-protection (RASP) solutions to detect attempts to manipulate application configuration
• Deploy intrusion detection systems (IDS) with signatures for Symfony-specific exploitation patterns

Monitoring Recommendations

• Enable detailed logging of all HTTP request query strings in web server access logs
• Configure alerts for any application environment changes detected at runtime
• Monitor for debug information appearing in HTTP responses that should be production-only
• Implement file integrity monitoring on Symfony configuration files to detect unauthorized changes

How to Mitigate CVE-2024-50340

Immediate Actions Required

• Upgrade to patched versions: Symfony Runtime 5.4.46, 6.4.14, or 7.1.7 or later
• Review PHP configuration and consider disabling register_argv_argc if CLI argument processing is not required
• Audit web server logs for potential exploitation attempts
• Verify application environment settings are correctly configured for production deployments

Patch Information

Symfony has released security patches in versions 5.4.46, 6.4.14, and 7.1.7. The fix modifies the SymfonyRuntime class to ignore $_SERVER['argv'] values for non-SAPI PHP runtimes by adding a check for empty($_GET) before processing argv input. Users should update their symfony/runtime dependency to the latest patched version.

For more details, see the GitHub Security Advisory and the GitHub Commit Details.

Workarounds

• There are no known workarounds for this vulnerability; upgrading is the only recommended mitigation
• As a defense-in-depth measure, ensure register_argv_argc is set to off in production PHP configurations if not explicitly required
• Implement WAF rules to filter requests containing suspicious query string patterns targeting Symfony internals

# Configuration example - Verify and update Symfony Runtime version
composer show symfony/runtime
composer require symfony/runtime:^5.4.46  # For 5.x branch
composer require symfony/runtime:^6.4.14  # For 6.x branch
composer require symfony/runtime:^7.1.7   # For 7.x branch

# Verify PHP register_argv_argc setting
php -i | grep register_argv_argc