CVE-2006-4339 in Server
Summary
by MITRE
OpenSSL before 0.9.7, 0.9.7 before 0.9.7k, and 0.9.8 before 0.9.8c, when using an RSA key with exponent 3, removes PKCS-1 padding before generating a hash, which allows remote attackers to forge a PKCS #1 v1.5 signature that is signed by that RSA key and prevents OpenSSL from correctly verifying X.509 and other certificates that use PKCS #1.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 01/13/2025
This vulnerability affects OpenSSL versions prior to specific patch releases, creating a critical weakness in cryptographic signature verification processes. The flaw specifically manifests when OpenSSL processes RSA keys with exponent 3, a common configuration in many cryptographic implementations. The vulnerability stems from improper handling of PKCS-1 padding during signature generation and verification operations. When an RSA key with exponent 3 is used, the software removes PKCS-1 padding before creating the hash value, which fundamentally undermines the security guarantees provided by the PKCS-1 standard. This behavior creates a significant gap in the cryptographic protocol that malicious actors can exploit to generate fraudulent signatures.
The technical impact of this vulnerability extends beyond simple signature forgery, as it specifically targets the integrity verification mechanisms of X.509 certificates and other PKCS #1 based cryptographic objects. The removal of PKCS-1 padding before hash generation creates a condition where attackers can construct valid-looking signatures that OpenSSL will accept as authentic. This weakness directly violates the fundamental principles of public key cryptography where proper padding ensures the integrity and authenticity of digital signatures. The vulnerability is particularly dangerous because it operates at the core cryptographic layer, potentially allowing attackers to bypass certificate validation entirely and impersonate legitimate entities within secure communications.
From an operational perspective, this vulnerability creates a substantial risk for systems relying on OpenSSL for secure communications, certificate validation, and digital signature operations. The impact is severe as it enables man-in-the-middle attacks, certificate impersonation, and the potential compromise of entire cryptographic infrastructures. Systems using RSA keys with exponent 3 are particularly vulnerable, which includes many web servers, email systems, and cryptographic applications that default to this configuration. The vulnerability affects not just the signature generation process but also the certificate verification mechanisms that depend on proper PKCS-1 validation. This weakness can be exploited across multiple protocols including SSL/TLS, S/MIME, and other systems that rely on OpenSSL's cryptographic libraries for security.
The remediation strategy involves upgrading to patched versions of OpenSSL where the improper padding handling has been corrected. Organizations must ensure all systems using affected OpenSSL versions are updated to versions 0.9.7k, 0.9.8c, or later. Additionally, systems should be audited to identify RSA keys with exponent 3 and potentially reconfigure them to use larger exponents or implement proper padding validation. Security teams should also monitor for any attempts to exploit this vulnerability through signature forgery attacks and implement network monitoring to detect anomalous certificate validation behavior. This vulnerability aligns with CWE-327, which addresses the use of weak cryptographic algorithms and improper padding implementations, and maps to ATT&CK technique T1553.004 related to credentials from password storage modules, as the compromised signature validation can lead to unauthorized access through forged certificates.
The broader implications of this vulnerability highlight the critical importance of proper cryptographic implementation and the dangers of shortcuts in security protocols. The issue demonstrates how seemingly minor implementation details in cryptographic libraries can create fundamental security weaknesses that undermine entire security architectures. Organizations should implement comprehensive cryptographic hygiene practices, including regular security audits of cryptographic libraries and configurations, proper key management procedures, and continuous monitoring for similar vulnerabilities in other cryptographic components. The vulnerability serves as a reminder that even well-established cryptographic libraries require careful attention to implementation details and regular security updates to maintain their effectiveness against evolving threats.