CVE-2011-1398 in PHP
Summary
by MITRE
The sapi_header_op function in main/SAPI.c in PHP before 5.3.11 and 5.4.x before 5.4.0RC2 does not check for %0D sequences (aka carriage return characters), which allows remote attackers to bypass an HTTP response-splitting protection mechanism via a crafted URL, related to improper interaction between the PHP header function and certain browsers, as demonstrated by Internet Explorer and Google Chrome.
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Analysis
by VulDB Data Team • 11/27/2024
The vulnerability identified as CVE-2011-1398 represents a critical HTTP response-splitting flaw in PHP's Server API (SAPI) implementation that affects versions prior to 5.3.11 and 5.4.0RC2. This security weakness stems from the sapi_header_op function in main/SAPI.c failing to properly validate and sanitize input sequences containing carriage return characters represented as %0D. The flaw specifically targets the interaction between PHP's header handling mechanism and web browsers, creating a pathway for malicious actors to manipulate HTTP responses through carefully crafted URLs. The vulnerability's exploitation potential is particularly concerning given that it affects widely deployed web applications built on PHP infrastructure, where header manipulation can lead to various downstream security consequences including session hijacking, cross-site scripting attacks, and cache poisoning.
The technical implementation of this vulnerability exploits the improper handling of URL-encoded characters within PHP's SAPI layer, where the %0D sequence representing carriage return characters is not adequately filtered or escaped during header processing. This failure creates a condition where attackers can inject malicious content into HTTP headers, effectively splitting the response and allowing them to inject additional headers or content that should not be present in the original response. The vulnerability specifically demonstrates how browser-specific behaviors can be leveraged to bypass security protections, with Internet Explorer and Google Chrome exhibiting particular susceptibility to this form of header manipulation. The issue is classified under CWE-1107, which addresses improper interaction between different security mechanisms, and aligns with ATT&CK technique T1190 for exploiting vulnerabilities in web applications.
The operational impact of CVE-2011-1398 extends beyond simple header injection, as it can enable attackers to perform sophisticated attacks that compromise user sessions and web application integrity. When exploited, this vulnerability allows adversaries to inject malicious headers that could redirect users to phishing sites, inject malicious JavaScript code, or manipulate browser behavior in ways that undermine the security model of the web application. The vulnerability's presence in PHP's core SAPI functionality means that any application using PHP's header functions for redirecting users, setting cookies, or managing authentication tokens becomes potentially vulnerable. Organizations running affected PHP versions face significant risk of unauthorized access and data compromise, particularly in environments where PHP applications handle sensitive user information or implement authentication mechanisms that rely on proper header management.
Mitigation strategies for CVE-2011-1398 primarily focus on immediate version upgrades to PHP 5.3.11 or 5.4.0RC2 and later releases where the vulnerability has been addressed through proper input validation and sanitization of header sequences. System administrators should conduct comprehensive vulnerability assessments to identify all PHP installations within their infrastructure and ensure all affected systems receive timely updates. Additionally, implementing proper input validation at application level can provide defense-in-depth measures, including sanitizing user-supplied data before passing it to PHP header functions and employing web application firewalls to detect and block suspicious URL patterns containing %0D sequences. Organizations should also consider implementing strict header validation policies and monitoring for anomalous header injection attempts, as the vulnerability can be detected through network traffic analysis and application logs. The remediation process must include thorough testing of updated systems to ensure that the security patch does not introduce compatibility issues with existing web applications while maintaining the integrity of header handling functionality.