CVE-2024-8925: PHP Multipart Form Parsing Vulnerability

CVE-2024-8925 Overview

CVE-2024-8925 is an HTTP Request Smuggling vulnerability affecting PHP's multipart form data parsing mechanism. In vulnerable PHP versions, erroneous parsing of multipart form data contained in HTTP POST requests could lead to legitimate data not being processed correctly. This allows a malicious attacker who can control part of the submitted data to exclude portions of other data, potentially leading to erroneous application behavior.

Critical Impact

Attackers can manipulate multipart form data parsing to exclude legitimate user-submitted data, potentially bypassing security controls, corrupting application state, or causing business logic failures in web applications.

Affected Products

• PHP 8.1.* versions before 8.1.30
• PHP 8.2.* versions before 8.2.24
• PHP 8.3.* versions before 8.3.12

Discovery Timeline

• 2024-10-08 - CVE-2024-8925 published to NVD
• 2025-11-03 - Last updated in NVD database

Technical Details for CVE-2024-8925

Vulnerability Analysis

This vulnerability (CWE-444: Inconsistent Interpretation of HTTP Requests, also known as HTTP Request Smuggling) resides in PHP's core multipart form data parsing functionality. When processing HTTP POST requests with multipart/form-data content type, the PHP interpreter fails to correctly handle certain malformed boundary conditions or specially crafted data segments.

The flaw enables an attacker who can inject or control a portion of form data within an HTTP request to influence how PHP parses the entire request body. This parsing inconsistency can result in legitimate form fields being silently dropped or ignored, while the attacker-controlled data is processed normally.

The attack surface is significant because multipart form data is the standard encoding for file uploads and complex form submissions across web applications. Any PHP application accepting file uploads or processing forms with multiple fields could be affected.

Root Cause

The root cause lies in PHP's multipart form data parser not properly handling edge cases in boundary detection and field delimitation. When encountering specially crafted content that exploits these parsing inconsistencies, the parser may incorrectly identify field boundaries, causing subsequent legitimate data fields to be excluded from the parsed result.

Attack Vector

This vulnerability is exploitable over the network without requiring authentication or user interaction. An attacker can craft a malicious HTTP POST request with carefully constructed multipart form data that exploits the parsing flaw. The attack requires the ability to submit data to a vulnerable PHP application.

The exploitation scenario involves:

1. The attacker identifies a PHP application endpoint that accepts multipart form data
2. The attacker crafts a POST request with malformed boundary markers or field structures
3. The malicious payload causes PHP to misparse the request, excluding legitimate data
4. The application processes the manipulated data, potentially bypassing validation or altering business logic

For detailed technical information on the parsing vulnerability, see the PHP Security Advisory.

Detection Methods for CVE-2024-8925

Indicators of Compromise

• Unusual or malformed multipart boundary strings in HTTP POST requests
• Application logs showing missing expected form fields or incomplete data submissions
• HTTP requests with abnormally structured Content-Type: multipart/form-data headers
• Unexpected application behavior following form submissions that processed without errors

Detection Strategies

• Monitor web server access logs for POST requests with unusual multipart boundary patterns
• Implement input validation to detect and log requests where expected form fields are missing
• Deploy Web Application Firewall (WAF) rules to identify malformed multipart request structures
• Enable PHP error logging and monitor for parsing-related warnings or notices

Monitoring Recommendations

• Audit PHP version deployments across infrastructure to identify vulnerable installations
• Monitor application error logs for unexpected null or missing form field values
• Implement anomaly detection for form submission patterns that deviate from normal baselines
• Track EPSS score trends for this vulnerability to assess evolving exploitation likelihood

How to Mitigate CVE-2024-8925

Immediate Actions Required

• Upgrade PHP 8.1.x installations to version 8.1.30 or later
• Upgrade PHP 8.2.x installations to version 8.2.24 or later
• Upgrade PHP 8.3.x installations to version 8.3.12 or later
• Review application code for dependencies on multipart form data processing

Patch Information

PHP has released patched versions addressing this vulnerability. The fix corrects the multipart form data parsing logic to properly handle boundary conditions and prevent data exclusion attacks.

Security advisories and patch details are available from:

• PHP GitHub Security Advisory
• Debian LTS Security Announcement
• NetApp Security Advisory

Workarounds

• Implement server-side validation to verify all expected form fields are present before processing
• Deploy a Web Application Firewall with rules to normalize or reject malformed multipart requests
• Add application-level integrity checks to detect missing or manipulated form data
• Consider implementing request signing or HMAC validation for critical form submissions

# Check PHP version and upgrade on Debian/Ubuntu systems
php -v
sudo apt update
sudo apt install php8.3  # Install patched version 8.3.12+