CVE-2008-7129 in XySSL
Summary
by MITRE
XySSL before 0.9 allows remote attackers to cause a denial of service (infinite loop) via an X.509 certificate that does not pass the RSA signature check during verification.
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Analysis
by VulDB Data Team • 01/18/2019
The vulnerability identified as CVE-2008-7129 represents a critical denial of service weakness within the XySSL cryptographic library version 0.8 and earlier. This flaw manifests when the library processes X.509 certificates that fail RSA signature validation, creating a condition where the verification routine enters an infinite loop. The issue stems from inadequate error handling mechanisms within the certificate processing code, specifically during the cryptographic signature verification phase. Attackers can exploit this vulnerability by crafting malicious X.509 certificates that deliberately fail RSA signature checks, thereby triggering the problematic code path that leads to the infinite loop scenario.
From a technical perspective, the vulnerability operates at the cryptographic verification layer of the SSL/TLS implementation, where X.509 certificates are validated against their corresponding RSA signatures. When a certificate fails the signature verification process, the XySSL library should gracefully handle this failure and proceed with appropriate error reporting or certificate rejection. However, the flawed implementation contains a logic error where the verification routine becomes trapped in a continuous loop when encountering certificates that do not pass RSA signature validation. This infinite loop consumes excessive CPU resources and prevents the system from processing subsequent certificate verification requests, effectively rendering the service unavailable to legitimate users.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be leveraged in distributed denial of service attacks against systems relying on XySSL for secure communications. Network infrastructure components such as web servers, email servers, and SSL/TLS proxies that utilize this library become susceptible to exploitation, potentially affecting thousands of connected clients and services. The vulnerability affects any system that depends on XySSL for certificate validation, particularly those implementing secure communication protocols that require certificate verification. Organizations using vulnerable versions may experience complete service outages until the affected systems are patched or updated, making this a significant concern for security operations teams managing critical infrastructure.
Security practitioners should implement immediate mitigations including upgrading to XySSL version 0.9 or later, where the infinite loop has been resolved through proper error handling mechanisms. Additionally, network administrators should consider implementing certificate validation timeouts and monitoring for unusual CPU usage patterns that may indicate exploitation attempts. The vulnerability aligns with CWE-835, which specifically addresses infinite loops in software, and represents a classic example of improper error handling in cryptographic libraries. From an ATT&CK framework perspective, this vulnerability could be categorized under privilege escalation and denial of service tactics, as it allows attackers to consume system resources and potentially disrupt service availability. Organizations should also review their certificate management practices and implement certificate pinning where appropriate to reduce the attack surface. The fix implemented in version 0.9 demonstrates the importance of proper error handling in cryptographic libraries, as the developers addressed the root cause by ensuring that failed RSA signature verification does not result in infinite loop conditions.