CVE-2024-5458 Overview
CVE-2024-5458 is an input validation vulnerability affecting PHP's filter_var() function when used with the FILTER_VALIDATE_URL flag. Due to a code logic error in PHP versions 8.1.* before 8.1.29, 8.2.* before 8.2.20, and 8.3.* before 8.3.8, certain malformed URLs containing invalid user information (username and password components) are incorrectly treated as valid. This flaw may cause downstream applications to accept and parse URLs that should have been rejected, potentially leading to security bypass scenarios.
Critical Impact
Applications relying on PHP's URL validation may accept malformed URLs with invalid credentials, enabling potential URL parsing inconsistencies, SSRF attacks, or authentication bypass depending on how validated URLs are subsequently processed.
Affected Products
- PHP 8.1.* versions before 8.1.29
- PHP 8.2.* versions before 8.2.20
- PHP 8.3.* versions before 8.3.8
- Fedora 40
Discovery Timeline
- 2024-06-09 - CVE-2024-5458 published to NVD
- 2025-11-03 - Last updated in NVD database
Technical Details for CVE-2024-5458
Vulnerability Analysis
This vulnerability stems from insufficient verification of data authenticity (CWE-345) within PHP's URL filtering mechanism. When developers use filter_var($url, FILTER_VALIDATE_URL) to sanitize user-supplied URLs, the function is expected to reject malformed or potentially dangerous URL structures. However, due to a code logic error in the validation routine, certain URLs containing malformed user information components (the username:password@ portion of a URL) are incorrectly accepted as valid.
The impact of this vulnerability depends heavily on how applications process validated URLs. Common attack scenarios include:
- URL Parsing Discrepancies: Different URL parsers may interpret the malformed user information differently, leading to inconsistent behavior between validation and actual use
- SSRF Potential: If validated URLs are used in server-side requests, attackers may be able to craft URLs that bypass validation but redirect to unintended destinations
- Authentication Confusion: Applications parsing user credentials from URLs may extract incorrect or attacker-controlled values
Root Cause
The vulnerability exists due to a code logic error in PHP's ext/filter/logical_filters.c file, specifically in the URL validation logic. The filter implementation fails to properly validate the user information component of URLs according to RFC 3986 specifications. This allows specially crafted URLs with invalid characters or malformed structures in the username and password fields to pass validation when they should be rejected.
Attack Vector
The attack vector is network-based and requires no authentication or user interaction. An attacker can exploit this vulnerability by submitting malformed URLs to any PHP application that relies on filter_var() with FILTER_VALIDATE_URL for input validation. The exploitation process involves:
- Identifying a PHP application that validates URLs using filter_var($input, FILTER_VALIDATE_URL)
- Crafting a URL with malformed user information that exploits the validation bypass
- Submitting the malformed URL to the target application
- The application accepts the invalid URL as valid and processes it according to its intended purpose
The specific impact depends on how the application uses the validated URL—whether for redirects, server-side requests, display, or further parsing.
Detection Methods for CVE-2024-5458
Indicators of Compromise
- Web application logs showing unusual URL patterns with malformed user information components (e.g., URLs with special characters in the username/password section)
- Unexpected SSRF-like behavior in applications that process user-supplied URLs
- Application errors or anomalies when parsing URLs that were previously validated
Detection Strategies
- Audit PHP applications for use of filter_var() with FILTER_VALIDATE_URL flag and assess downstream URL processing logic
- Implement additional URL validation layers using parse_url() and manual verification of URL components
- Monitor web server logs for URL submissions containing unusual characters in the authority component
Monitoring Recommendations
- Enable verbose logging for applications that process user-supplied URLs to capture potential exploitation attempts
- Implement web application firewall (WAF) rules to flag URLs with suspicious patterns in user information fields
- Review application behavior when processing URLs from external sources
How to Mitigate CVE-2024-5458
Immediate Actions Required
- Upgrade PHP to version 8.1.29, 8.2.20, or 8.3.8 or later immediately
- Audit all applications using filter_var() with FILTER_VALIDATE_URL to assess exposure
- Implement defense-in-depth by adding secondary URL validation logic until patches can be applied
- Review downstream URL processing to understand potential impact of accepting malformed URLs
Patch Information
PHP has released security patches addressing this vulnerability in versions 8.1.29, 8.2.20, and 8.3.8. The fix corrects the code logic error in the URL validation routine to properly reject URLs with invalid user information components. Detailed information is available in the GitHub Security Advisory.
Distribution-specific patches are available:
Workarounds
- Implement additional validation using parse_url() to manually verify URL components after filter_var() validation
- Use allowlists for URL schemes and hosts where possible to limit the attack surface
- Consider using third-party URL validation libraries that provide stricter parsing until PHP can be upgraded
- Deploy WAF rules to filter potentially malformed URLs at the network perimeter
# Check current PHP version and verify if vulnerable
php -v
# Update PHP on Debian/Ubuntu-based systems
sudo apt update && sudo apt upgrade php
# Update PHP on RHEL/Fedora-based systems
sudo dnf update php
# Verify the updated version is patched (8.1.29+, 8.2.20+, or 8.3.8+)
php -v
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
