CVE-2013-4248 in PHP
Summary
by MITRE
The openssl_x509_parse function in openssl.c in the OpenSSL module in PHP before 5.4.18 and 5.5.x before 5.5.2 does not properly handle a \0 character in a domain name in the Subject Alternative Name field of an X.509 certificate, which allows man-in-the-middle attackers to spoof arbitrary SSL servers via a crafted certificate issued by a legitimate Certification Authority, a related issue to CVE-2009-2408.
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Analysis
by VulDB Data Team • 05/21/2021
The vulnerability identified as CVE-2013-4248 represents a critical flaw in PHP's OpenSSL module that affects versions prior to 5.4.18 and 5.5.x before 5.5.2. This issue stems from improper handling of null characters within the Subject Alternative Name field of X.509 certificates, creating a significant security weakness that enables sophisticated man-in-the-middle attacks. The flaw specifically impacts the openssl_x509_parse function in openssl.c, which processes X.509 certificate data within PHP applications. When a certificate contains a null character embedded within a domain name string in the Subject Alternative Name extension, the parsing function fails to properly validate or sanitize this input, leading to potential certificate validation bypasses. This vulnerability operates at the intersection of certificate parsing logic and security validation, creating a pathway for attackers to craft malicious certificates that appear legitimate to vulnerable PHP applications.
The technical implementation of this vulnerability exploits the way PHP's OpenSSL module processes certificate data structures, particularly focusing on how null characters are handled within string parsing operations. The flaw allows an attacker to insert a null character within a domain name within the Subject Alternative Name field, effectively truncating the domain name during parsing while maintaining the certificate's apparent validity. This creates a situation where a certificate issued by a legitimate Certification Authority can be manipulated to include a null-terminated domain name that matches the target domain, enabling attackers to establish fraudulent SSL connections that appear authentic to PHP applications. The vulnerability directly relates to CWE-129, which addresses improper validation of length or count parameters, and CWE-20, which covers input validation issues. The attack vector involves constructing a certificate with malicious null character placement that bypasses normal certificate validation checks while maintaining syntactic correctness.
The operational impact of CVE-2013-4248 extends beyond simple certificate validation failures, creating a comprehensive attack surface for man-in-the-middle scenarios across web applications that rely on PHP for SSL/TLS certificate validation. Applications using vulnerable PHP versions become susceptible to certificate spoofing attacks where attackers can impersonate legitimate websites by presenting certificates that contain null characters in their Subject Alternative Name fields. This vulnerability affects web servers, API endpoints, and any PHP-based application that performs SSL certificate validation, potentially compromising sensitive data transmission, user authentication, and overall system integrity. The attack can be executed against any service that uses PHP's OpenSSL functions for certificate verification, making it particularly dangerous in environments where multiple applications depend on shared certificate validation logic. Organizations running vulnerable PHP versions face significant risk of data interception, session hijacking, and credential theft through this vulnerability.
Mitigation strategies for CVE-2013-4248 require immediate patching of affected PHP installations to versions 5.4.18 or 5.5.2 and later, which contain the necessary fixes for proper null character handling in certificate parsing. System administrators should prioritize updating PHP installations across all production environments and verify that the updates have been successfully applied. Additional defensive measures include implementing certificate pinning mechanisms, enhancing certificate validation procedures, and monitoring for suspicious certificate usage patterns. Organizations should also consider deploying network-based intrusion detection systems that can identify potential certificate manipulation attempts and implement strict certificate validation policies that go beyond default PHP behavior. The vulnerability's relationship to ATT&CK technique T1552.001 emphasizes the importance of protecting credential access and network communication through enhanced certificate validation controls. Regular security audits and vulnerability assessments should include checks for PHP version compliance and proper certificate handling implementations to prevent exploitation of similar parsing vulnerabilities in the future.