CVE-2003-0543 in OpenSSL
Summary
by MITRE
Integer overflow in OpenSSL 0.9.6 and 0.9.7 allows remote attackers to cause a denial of service (crash) via an SSL client certificate with certain ASN.1 tag values.
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Analysis
by VulDB Data Team • 12/26/2024
The vulnerability described in CVE-2003-0543 represents a critical integer overflow flaw within the OpenSSL cryptographic library version 0.9.6 and 0.9.7. This issue manifests when the SSL client certificate processing routine encounters specific ASN.1 tag values that trigger improper integer handling during certificate parsing. The flaw operates at the core of OpenSSL's certificate validation mechanism, where the library fails to properly validate the size of certain integer fields within the ASN.1 encoded certificate structure. When an attacker crafts a malicious client certificate containing oversized or malformed ASN.1 tag values, the integer overflow condition causes the application to crash or become unresponsive, resulting in a denial of service condition that affects legitimate users attempting to establish secure connections.
The technical implementation of this vulnerability stems from insufficient bounds checking during the parsing of ASN.1 structures within the OpenSSL library. Specifically, when processing client certificates, the software performs arithmetic operations on integer values that represent the length of various certificate components without proper validation of whether these values exceed the maximum representable integer limits. This type of vulnerability maps directly to CWE-190, which describes integer overflow conditions, and more specifically to CWE-128, which addresses signed integer overflow. The flaw occurs in the certificate parsing code path where the library attempts to allocate memory or perform calculations based on the parsed ASN.1 tag values, and when these values are manipulated to exceed integer limits, the subsequent operations cause system instability.
The operational impact of this vulnerability extends beyond simple service disruption, as it provides attackers with a method to systematically crash SSL services without requiring authentication or advanced privileges. Any service running OpenSSL 0.9.6 or 0.9.7 that accepts client certificates becomes vulnerable to this attack, including web servers, email servers, and any application that implements SSL/TLS client authentication. The attack vector is particularly concerning because it can be executed remotely through standard SSL connection establishment processes, making it difficult to distinguish from legitimate traffic. This vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and represents a classic example of how cryptographic libraries can become attack surfaces when proper input validation is absent. The vulnerability affects not only web applications but also any system that relies on OpenSSL for secure communications, creating widespread potential impact across enterprise networks and internet-facing services.
Mitigation strategies for CVE-2003-0543 require immediate patching of affected OpenSSL versions to the latest stable releases that contain the necessary integer overflow protections. Organizations should prioritize updating their OpenSSL installations to versions 0.9.7a or later, which include fixes for the integer overflow conditions in certificate parsing. Additionally, system administrators should implement network-level monitoring to detect unusual SSL connection patterns that might indicate exploitation attempts, particularly around client certificate validation phases. The implementation of certificate validation policies that limit the size and complexity of accepted certificates can serve as an additional defensive measure, though this approach is less effective than proper patching. Security teams should also consider implementing intrusion detection systems capable of identifying malformed ASN.1 structures and monitoring for abnormal memory allocation patterns that might indicate exploitation attempts. Organizations should conduct thorough vulnerability assessments to identify all systems running affected OpenSSL versions and establish automated patch management processes to prevent similar vulnerabilities from being exploited in the future.