CVE-2006-7239 in gnutls
Summary
by MITRE
The _gnutls_x509_oid2mac_algorithm function in lib/gnutls_algorithms.c in GnuTLS before 1.4.2 allows remote attackers to cause a denial of service (crash) via a crafted X.509 certificate that uses a hash algorithm that is not supported by GnuTLS, which triggers a NULL pointer dereference.
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Analysis
by VulDB Data Team • 06/14/2025
The vulnerability identified as CVE-2006-7239 represents a critical denial of service flaw within the GnuTLS cryptographic library version 1.4.2 and earlier. This issue stems from inadequate input validation in the _gnutls_x509_oid2mac_algorithm function located in the lib/gnutls_algorithms.c file. The flaw manifests when the library processes X.509 certificates containing hash algorithms that fall outside the supported set of cryptographic operations. When such unsupported algorithms are encountered, the function fails to properly handle the scenario, leading to a NULL pointer dereference that ultimately causes the application to crash. This vulnerability specifically targets the certificate processing pipeline where GnuTLS attempts to map Object Identifier (OID) values to corresponding MAC (Message Authentication Code) algorithms for cryptographic operations.
The technical exploitation of this vulnerability requires an attacker to construct a malicious X.509 certificate containing an unsupported hash algorithm OID. When the vulnerable GnuTLS library processes this certificate, the _gnutls_x509_oid2mac_algorithm function attempts to dereference a NULL pointer that should have been properly initialized or validated. This NULL pointer dereference constitutes a classic software bug that violates fundamental memory safety principles and falls under CWE-476 which specifically addresses NULL pointer dereference vulnerabilities. The vulnerability operates at the cryptographic protocol level where X.509 certificates are parsed and validated, making it particularly dangerous as it can be triggered during normal SSL/TLS handshake operations or certificate validation processes.
The operational impact of CVE-2006-7239 extends beyond simple service disruption to potentially compromise the availability of cryptographic services that depend on GnuTLS. Systems utilizing vulnerable versions of GnuTLS for SSL/TLS connections, certificate validation, or cryptographic operations become susceptible to denial of service attacks that can render services unavailable to legitimate users. This vulnerability affects a broad range of applications and systems that rely on GnuTLS for secure communications, including web servers, mail servers, VPN services, and any software implementing TLS/SSL protocols. The attack vector is particularly concerning as it requires minimal privileges and can be executed remotely, making it an attractive target for attackers seeking to disrupt services without requiring elevated access rights. The vulnerability aligns with ATT&CK technique T1499.004 which covers network denial of service attacks, and specifically targets the availability component of the CIA triad.
Mitigation strategies for this vulnerability primarily involve upgrading to GnuTLS version 1.4.2 or later, where the NULL pointer dereference has been addressed through proper input validation and error handling. System administrators should prioritize patching affected systems and monitoring for potential exploitation attempts. Additional defensive measures include implementing certificate validation policies that reject certificates with unsupported algorithms, deploying intrusion detection systems to monitor for malformed certificate traffic, and configuring applications to handle cryptographic errors gracefully. The fix implemented in version 1.4.2 likely involved adding proper NULL pointer checks and ensuring that unsupported algorithms are handled gracefully rather than causing application crashes, which aligns with secure coding practices recommended in the CERT Secure Coding Standards for preventing memory safety vulnerabilities. Organizations should also consider implementing certificate pinning mechanisms and monitoring certificate issuance to prevent the deployment of malicious certificates that could trigger this vulnerability.