CVE-2004-2531 in GnuTLS
Summary
by MITRE
X.509 Certificate Signature Verification in Gnu transport layer security library (GnuTLS) 1.0.16 allows remote attackers to cause a denial of service (CPU consumption) via certificates containing long chains and signed with large RSA keys.
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Analysis
by VulDB Data Team • 06/29/2018
The vulnerability identified as CVE-2004-2531 represents a significant denial of service weakness within the GNU Transport Layer Security library version 1.0.16. This flaw specifically impacts the X.509 certificate signature verification process, which is fundamental to establishing secure communications in TLS environments. The issue arises when the library processes certificates that contain extended chains and are signed using large RSA keys, creating a scenario where computational resources become excessively consumed during the verification phase.
The technical root cause of this vulnerability lies in the inefficient handling of certificate chains and signature verification algorithms within GnuTLS. When processing certificates with long chains and large RSA key sizes, the library's signature verification routine enters into computationally intensive loops that can consume excessive CPU cycles. This behavior manifests as a denial of service condition where legitimate system resources become saturated, preventing the system from processing other valid requests. The vulnerability operates at the cryptographic validation layer, affecting the core security functionality that ensures certificate authenticity and integrity.
From an operational perspective, this vulnerability presents a substantial risk to systems relying on GnuTLS for secure communications, particularly those handling high volumes of certificate validation requests. Attackers can exploit this weakness by presenting specially crafted certificates containing extended chains and large RSA signatures, causing the target system to consume disproportionate CPU resources. The impact extends beyond simple service disruption as the excessive CPU consumption can lead to system instability, performance degradation, and potential complete service unavailability. This vulnerability specifically aligns with CWE-400, which addresses unchecked resource consumption, and demonstrates how cryptographic processing can become a vector for resource exhaustion attacks.
The attack surface for this vulnerability encompasses any system utilizing GnuTLS 1.0.16 for TLS connections, including web servers, mail servers, and any application requiring secure communication. The exploitation requires minimal privileges as the attack can be mounted remotely through network connections that establish TLS sessions. Systems with high connection throughput or those serving as certificate authorities become particularly vulnerable due to the increased frequency of certificate validation operations. This vulnerability also intersects with ATT&CK technique T1499.004, which covers network denial of service attacks, and T1595.001, which involves network infiltration through credential manipulation.
Mitigation strategies for CVE-2004-2531 primarily involve upgrading to a patched version of GnuTLS where the certificate verification process has been optimized to handle long chains and large RSA keys more efficiently. System administrators should implement certificate validation timeouts and rate limiting to prevent prolonged processing of suspicious certificates. Additionally, monitoring CPU utilization patterns and implementing intrusion detection systems can help identify exploitation attempts. Organizations should also consider implementing certificate pre-validation mechanisms and establishing automated patch management processes to ensure timely remediation of such vulnerabilities. The fix typically involves algorithmic improvements in the signature verification routine to prevent exponential time complexity when processing extended certificate chains.