CVE-2025-1736 Overview
CVE-2025-1736 is an input validation vulnerability affecting multiple versions of PHP. When user-supplied headers are sent, insufficient validation of end-of-line characters may prevent certain headers from being sent correctly or lead to header misinterpretation. This vulnerability falls under CWE-20 (Improper Input Validation) and impacts the integrity of HTTP header handling in PHP applications.
Critical Impact
Improper end-of-line character validation in PHP's header handling can lead to header injection attacks, bypassing security controls, or causing unexpected application behavior when processing HTTP headers.
Affected Products
- PHP 8.1.* before 8.1.32
- PHP 8.2.* before 8.2.28
- PHP 8.3.* before 8.3.19
- PHP 8.4.* before 8.4.5
- NetApp ONTAP 9
Discovery Timeline
- 2025-03-30 - CVE-2025-1736 published to NVD
- 2025-11-03 - Last updated in NVD database
Technical Details for CVE-2025-1736
Vulnerability Analysis
This vulnerability stems from improper input validation in PHP's header handling mechanism. When PHP applications process user-supplied HTTP headers, the end-of-line (EOL) character validation is insufficient. This inadequate validation can result in two primary issues: certain legitimate headers may fail to be transmitted, or headers may be misinterpreted by receiving systems.
The attack requires network access and involves some complexity, as it depends on specific conditions being met regarding how user input flows into header generation. While the vulnerability primarily affects confidentiality with limited impact, it does not require any privileges or user interaction to exploit.
Root Cause
The root cause is improper input validation (CWE-20) in PHP's header processing functionality. The validation logic for end-of-line characters within HTTP headers does not adequately handle all edge cases, allowing specially crafted input to bypass header validation checks. This can lead to header injection scenarios where attackers manipulate how headers are parsed and interpreted.
Attack Vector
The attack vector is network-based. An attacker can exploit this vulnerability by providing malicious input that includes improperly validated end-of-line characters in contexts where user data is incorporated into HTTP headers. When PHP processes these headers, the insufficient EOL validation allows the attacker's input to either:
- Prevent legitimate headers from being sent
- Cause headers to be misinterpreted by the server or downstream systems
This could potentially be leveraged for HTTP response splitting attacks, cache poisoning, or bypassing security controls that depend on proper header parsing.
Detection Methods for CVE-2025-1736
Indicators of Compromise
- Unexpected HTTP header formatting in application logs
- Anomalous end-of-line characters in header values within web server access logs
- HTTP response splitting patterns in traffic analysis
- Cache poisoning indicators in CDN or proxy logs
Detection Strategies
- Monitor web application firewall (WAF) logs for header injection attempts containing unusual line-ending sequences
- Implement log analysis rules to detect malformed HTTP headers in application traffic
- Deploy network-based intrusion detection signatures for HTTP header manipulation patterns
- Review PHP application logs for header-related errors or warnings
Monitoring Recommendations
- Enable verbose logging for PHP applications processing user-supplied headers
- Configure WAF rules to inspect and log suspicious header manipulation attempts
- Monitor for unusual patterns in HTTP response headers from PHP applications
- Set up alerts for HTTP response splitting signatures in network traffic
How to Mitigate CVE-2025-1736
Immediate Actions Required
- Update PHP installations to patched versions: 8.1.32, 8.2.28, 8.3.19, or 8.4.5 or later
- Review and audit application code that passes user input to header functions
- Implement additional input validation for any user-controlled data used in HTTP headers
- Deploy WAF rules to filter suspicious header injection attempts as a temporary measure
Patch Information
PHP has released security updates addressing this vulnerability. Upgrade to the following minimum versions based on your PHP branch:
- PHP 8.1: Upgrade to 8.1.32 or later
- PHP 8.2: Upgrade to 8.2.28 or later
- PHP 8.3: Upgrade to 8.3.19 or later
- PHP 8.4: Upgrade to 8.4.5 or later
For detailed patch information, refer to the PHP GitHub Security Advisory. NetApp ONTAP users should consult the NetApp Security Advisory for guidance on affected versions. Debian users can find distribution-specific updates in the Debian LTS Announcement.
Workarounds
- Implement strict input validation and sanitization for all user-supplied data before using it in HTTP headers
- Use PHP's header_remove() function to clear potentially tainted headers before setting new ones
- Deploy a web application firewall configured to detect and block header injection patterns
- Consider using framework-level abstractions for header management that provide additional validation
# Verify PHP version after patching
php -v
# Check for vulnerable PHP versions in your environment
find /usr -name "php" -exec {} -v \; 2>/dev/null | grep -E "PHP 8\.[1-4]\."
# Example: Updating PHP on Debian/Ubuntu
sudo apt update && sudo apt upgrade php
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
