CVE-2009-3291 in PHP
Summary
by MITRE
The php_openssl_apply_verification_policy function in PHP before 5.2.11 does not properly perform certificate validation, which has unknown impact and attack vectors, probably related to an ability to spoof certificates.
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Analysis
by VulDB Data Team • 04/08/2025
The vulnerability identified as CVE-2009-3291 resides within the php_openssl_apply_verification_policy function of PHP versions prior to 5.2.11, representing a critical flaw in the certificate validation mechanism that underpins secure communications. This weakness specifically affects the OpenSSL extension's certificate verification process, where the function fails to properly validate SSL/TLS certificates during PHP's secure socket communications. The vulnerability stems from insufficient certificate chain validation and trust verification, creating potential pathways for malicious actors to exploit the trust model that PHP relies upon for establishing secure connections to remote servers. The incomplete implementation of certificate validation means that PHP applications may accept certificates that should be rejected based on standard security protocols, effectively undermining the cryptographic security assurances that SSL/TLS certificates are designed to provide. This issue falls under the broader category of certificate validation failures that can lead to man-in-the-middle attacks and unauthorized access to sensitive data, as described in CWE-295 which specifically addresses improper certificate validation.
The technical nature of this vulnerability manifests when PHP applications establish SSL/TLS connections to external services, particularly those using certificate-based authentication. During the connection establishment process, the php_openssl_apply_verification_policy function should validate certificate chains, check certificate expiration dates, verify certificate authorities, and ensure proper hostname matching. However, the flaw in the implementation allows certain malformed or unauthorized certificates to pass validation when they should be rejected, potentially enabling attackers to present fake certificates that PHP will accept as legitimate. This weakness particularly impacts web applications that rely on PHP for secure communications with databases, external APIs, or other services requiring SSL/TLS encryption. The attack surface extends to any PHP application that uses SSL/TLS connections for authentication or data transmission, making it a widespread concern across numerous web applications and services. The vulnerability's impact is particularly concerning because it operates at the core of PHP's security infrastructure, affecting the fundamental trust model that secure communications depend upon.
The operational impact of CVE-2009-3291 extends far beyond simple certificate acceptance issues, potentially enabling sophisticated attacks that can compromise entire application infrastructures. Attackers could exploit this vulnerability by presenting forged certificates that appear legitimate to PHP applications, allowing them to intercept and manipulate communications between applications and their remote services. This capability directly aligns with techniques described in the MITRE ATT&CK framework under the T1573.002 sub-technique for "Encrypted Channel" and T1566.001 for "Phishing", as it enables attackers to establish fraudulent secure connections that bypass normal security controls. The vulnerability could allow attackers to perform session hijacking, data exfiltration, or even gain unauthorized access to backend systems that rely on certificate-based authentication. Applications using PHP for secure communications with databases, external APIs, or cloud services become particularly vulnerable, as attackers could exploit this weakness to access sensitive information or manipulate transactions. The long-term implications include potential compromise of user credentials, financial data, and confidential business information, as the vulnerability affects the fundamental security assurances provided by SSL/TLS protocols. Organizations running PHP applications without proper patches are left exposed to these risks, making this vulnerability a significant concern for enterprise security teams.
The recommended mitigation strategy for CVE-2009-3291 involves immediate patching of all affected PHP installations to versions 5.2.11 or later, where the certificate validation implementation has been corrected. System administrators should conduct comprehensive inventory assessments to identify all PHP applications and servers that may be affected by this vulnerability, particularly those handling sensitive data or requiring secure communications. Organizations should implement network monitoring to detect potential exploitation attempts and establish robust certificate management practices to ensure that only trusted certificates are accepted by PHP applications. Additional protective measures include configuring PHP applications to use explicit certificate verification settings, implementing certificate pinning where appropriate, and establishing regular security audits of SSL/TLS configurations. The vulnerability's classification as a certificate validation failure aligns with industry best practices for secure coding and configuration management, emphasizing the importance of proper certificate handling in secure communications. Security teams should also consider implementing intrusion detection systems that can identify suspicious certificate validation patterns and establish incident response procedures specifically tailored to address SSL/TLS certificate-related security incidents. Organizations should prioritize patch management processes to ensure that all PHP installations remain up-to-date with security patches, as this vulnerability represents a persistent risk to applications that do not receive timely updates.