CVE-2003-0544 in OpenSSL
Summary
by MITRE
OpenSSL 0.9.6 and 0.9.7 does not properly track the number of characters in certain ASN.1 inputs, which allows remote attackers to cause a denial of service (crash) via an SSL client certificate that causes OpenSSL to read past the end of a buffer when the long form is used.
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Analysis
by VulDB Data Team • 12/26/2024
The vulnerability described in CVE-2003-0544 represents a critical buffer over-read condition within OpenSSL versions 0.9.6 and 0.9.7 that specifically affects the handling of ASN.1 (Abstract Syntax Notation One) encoded data structures. This flaw occurs during the processing of SSL client certificates where OpenSSL fails to properly validate the length field of ASN.1 inputs, particularly when the long form encoding is utilized. The issue stems from the OpenSSL library's inadequate boundary checking mechanisms when parsing certificate data, creating a scenario where maliciously crafted certificates can trigger memory access violations.
The technical implementation of this vulnerability exploits the ASN.1 parsing logic within OpenSSL's certificate validation routines. When an SSL client presents a certificate using the long form encoding for length fields, the library does not correctly verify that the specified length corresponds to valid memory boundaries. This allows an attacker to craft a certificate with malformed length indicators that cause the OpenSSL parser to attempt reading beyond allocated buffer boundaries. The flaw specifically manifests in the ASN.1 decoder functions that handle the indefinite length encoding format, where the parser expects a specific pattern of length octets that may not be properly validated against the actual data size.
From an operational perspective, this vulnerability creates a significant denial of service risk for systems running vulnerable OpenSSL versions. An attacker can remotely trigger a crash of SSL services by presenting a specially crafted client certificate during the SSL handshake process, effectively causing the server to terminate unexpectedly. The impact extends beyond simple service disruption as this vulnerability can be exploited in a variety of scenarios including web servers, email servers, and any system relying on SSL/TLS for secure communications. The vulnerability is particularly concerning because it requires no authentication or special privileges beyond the ability to establish an SSL connection, making it highly exploitable in network-based attacks.
The vulnerability aligns with CWE-129, which describes improper validation of length fields, and represents a classic buffer over-read condition that can lead to system instability and potential information disclosure. From an ATT&CK framework perspective, this vulnerability maps to T1499.004 (Network Denial of Service) and potentially T1595.001 (Network Reconnaissance) as attackers may use it to identify vulnerable systems. The flaw demonstrates poor input validation practices in cryptographic libraries and highlights the critical importance of robust boundary checking in security-sensitive code. Organizations should immediately upgrade to OpenSSL versions 0.9.7a or later, which contain the necessary patches to properly validate ASN.1 length fields and prevent the buffer over-read conditions. Additionally, implementing proper certificate validation policies and monitoring for unusual SSL handshake patterns can help detect potential exploitation attempts. System administrators should also consider deploying intrusion detection systems that can identify malformed SSL certificate structures and establish network segmentation to limit the potential impact of such attacks.