CVE-2012-4388 in PHP
Summary
by MITRE • 01/25/2023
The sapi_header_op function in main/SAPI.c in PHP 5.4.0RC2 through 5.4.0 does not properly determine a pointer during checks 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. NOTE: this vulnerability exists because of an incorrect fix for CVE-2011-1398.
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Analysis
by VulDB Data Team • 01/25/2023
The vulnerability described in CVE-2012-4388 represents a critical flaw in PHP's handling of HTTP headers within the sapi_header_op function located in main/SAPI.c. This issue affects PHP versions 5.4.0RC2 through 5.4.0 and stems from an improper implementation of pointer determination during checks for %0D sequences, which are carriage return characters that can be used to manipulate HTTP responses. The vulnerability specifically targets the HTTP response-splitting protection mechanism that should prevent attackers from injecting malicious headers into HTTP responses.
The technical flaw occurs when PHP processes URLs containing %0D sequences, which are URL-encoded carriage return characters. The sapi_header_op function fails to properly handle these sequences during header validation, allowing attackers to bypass the intended protection against response splitting. This improper interaction between PHP's header function and web browsers like Internet Explorer and Google Chrome creates a vector for attackers to inject malicious HTTP headers. The vulnerability is particularly concerning because it represents an incorrect fix for CVE-2011-1398, suggesting that the remediation efforts for a previous response-splitting vulnerability introduced new weaknesses in the codebase.
The operational impact of this vulnerability is significant as it enables remote attackers to perform HTTP response splitting attacks, potentially allowing them to inject malicious headers, redirect users to malicious sites, or manipulate browser behavior. Attackers can craft URLs that exploit this flaw to bypass security mechanisms designed to prevent header injection attacks, which can lead to various security consequences including session hijacking, cross-site scripting, or cache poisoning. The fact that this vulnerability affects major browsers like Internet Explorer and Google Chrome amplifies its potential impact, as it can be exploited across different client environments.
This vulnerability aligns with CWE-1107, which addresses improper interaction between multiple security features or mechanisms, and relates to ATT&CK technique T1071.004 for application layer protocol manipulation. The improper handling of %0D sequences demonstrates a failure in input validation and sanitization, where the system does not adequately process or reject potentially dangerous character sequences that could be used to manipulate HTTP responses. Organizations running affected PHP versions should prioritize immediate patching to address this vulnerability, as it represents a regression in security that could be exploited by attackers to bypass existing protections. The vulnerability also highlights the importance of thorough testing when implementing security fixes, as the attempted remediation for CVE-2011-1398 inadvertently introduced this new weakness in the header processing logic.