CVE-2003-0851 in OpenSSL
Summary
by MITRE
OpenSSL 0.9.6k allows remote attackers to cause a denial of service (crash via large recursion) via malformed ASN.1 sequences.
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Analysis
by VulDB Data Team • 01/22/2025
The vulnerability identified as CVE-2003-0851 represents a critical denial of service flaw within OpenSSL version 0.9.6k that stems from inadequate handling of malformed ASN.1 sequences. This issue manifests when the cryptographic library encounters specially crafted input data that triggers excessive recursive parsing operations, ultimately leading to system crashes and service unavailability. The vulnerability specifically affects the ASN.1 parsing routines within OpenSSL's certificate processing mechanisms, where the library fails to properly validate the depth and structure of nested elements in the Abstract Syntax Notation One encoded data structures.
The technical exploitation of this vulnerability occurs through the manipulation of ASN.1 sequence structures that contain excessive nesting or circular references, causing the OpenSSL library to enter infinite recursive loops during certificate validation processes. When a remote attacker crafts malicious certificate data with deeply nested ASN.1 elements, the library's parsing functions repeatedly call themselves without proper termination conditions, consuming system resources and eventually causing the application to crash. This recursive behavior directly maps to CWE-674, which describes "Uncontrolled Recursion" as a weakness where a function calls itself without proper bounds checking or termination conditions, and aligns with ATT&CK technique T1499.004 for "Endpoint Denial of Service" through resource exhaustion.
The operational impact of this vulnerability extends beyond simple service disruption to encompass broader security implications within environments relying on OpenSSL for secure communications. Systems utilizing vulnerable OpenSSL versions become susceptible to denial of service attacks that can be executed with minimal resources and technical expertise, making them attractive targets for malicious actors seeking to disrupt services. The vulnerability affects any application or service that depends on OpenSSL for SSL/TLS certificate validation, including web servers, email servers, and other network services that implement secure communication protocols. Network infrastructure components and enterprise applications that process untrusted certificate data are particularly at risk, as attackers can exploit this weakness to cause cascading failures across interconnected systems.
Mitigation strategies for CVE-2003-0851 require immediate implementation of OpenSSL version updates to patched releases that include proper bounds checking and recursion limits for ASN.1 parsing operations. Organizations should prioritize upgrading to OpenSSL 0.9.7 or later versions where the recursive parsing logic has been restructured to prevent infinite loops and implement proper depth limitations. Additionally, network administrators should consider implementing certificate validation policies that include pre-processing checks for malformed ASN.1 sequences and deploy intrusion detection systems capable of identifying suspicious certificate data patterns. The vulnerability demonstrates the importance of input validation and proper error handling in cryptographic libraries, as highlighted by CWE-248 which addresses "Exception Handling" weaknesses in software systems. Security teams should also implement monitoring solutions that track resource consumption patterns and alert on unusual memory usage that may indicate recursive parsing attempts, while maintaining regular vulnerability assessments to identify similar weaknesses in other cryptographic components throughout their infrastructure.