CVE-2002-0076 in Java Runtime Environment
Summary
by MITRE
Java Runtime Environment (JRE) Bytecode Verifier allows remote attackers to escape the Java sandbox and execute commands via an applet containing an illegal cast operation, as seen in (1) Microsoft VM build 3802 and earlier as used in Internet Explorer 4.x and 5.x, (2) Netscape 6.2.1 and earlier, and possibly other implementations that use vulnerable versions of SDK or JDK, aka a variant of the "Virtual Machine Verifier" vulnerability.
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Analysis
by VulDB Data Team • 12/30/2024
The vulnerability described in CVE-2002-0076 represents a critical security flaw in the Java Runtime Environment's bytecode verification mechanism that fundamentally undermines the security model designed to isolate Java applets from the underlying system. This vulnerability specifically targets the Java Virtual Machine's verifier component responsible for ensuring that bytecode conforms to Java language specifications and does not contain potentially harmful operations. The flaw allows attackers to craft malicious applets that exploit an illegal cast operation to bypass the security sandbox that normally prevents applets from executing system-level commands or accessing local resources. The vulnerability affects multiple implementations including Microsoft's Virtual Machine version 3802 and earlier, which was integrated into Internet Explorer 4.x and 5.x browsers, as well as Netscape 6.2.1 and earlier versions, demonstrating the widespread nature of this security weakness across different Java runtime implementations. This type of vulnerability directly violates the fundamental security principle of Java's sandbox model where untrusted code should be isolated from system resources.
The technical exploitation of this vulnerability occurs through a specific bytecode manipulation technique that takes advantage of a gap in the verification process. Attackers can construct applets containing illegal cast operations that, when processed by the vulnerable bytecode verifier, are incorrectly accepted as valid bytecode. This acceptance allows the malicious code to execute commands with the privileges of the user running the Java applet, effectively breaking out of the restricted environment that normally protects against file system access, network connections, and system command execution. The flaw operates at the level of the JVM's verification phase where bytecode is analyzed for compliance with Java specifications, and the failure to properly validate certain cast operations creates an opening for privilege escalation. This vulnerability is classified under CWE-254 as a "Security Feature" weakness, specifically representing a failure to properly implement security checks during code execution. The attack vector is particularly dangerous because it leverages the trust model of web browsers that execute Java applets without additional user confirmation, making it a prime target for drive-by attacks.
The operational impact of this vulnerability extends far beyond simple code execution, as it provides attackers with complete system compromise capabilities through browser-based attack vectors. When exploited, malicious applets can access local files, execute arbitrary system commands, establish network connections, and potentially install additional malware on the victim's system. The vulnerability's exploitation requires no special privileges from the user, as the attack occurs within the normal operation of web browsers that support Java applets. This makes it particularly dangerous in enterprise environments where users may be browsing untrusted websites or clicking on malicious links that deliver the exploit. The vulnerability's presence in widely deployed browser versions such as Internet Explorer 4.x and 5.x meant that a substantial portion of internet users were potentially exposed to this attack vector. Organizations that relied on Java applets for legitimate business applications faced increased risk of compromise, as the vulnerability could be exploited through various attack surfaces including email attachments, web-based applications, and malicious websites. This vulnerability directly maps to ATT&CK technique T1059 which involves executing commands through various system interfaces, and T1071 which covers application layer protocols and network communication.
Mitigation strategies for this vulnerability required immediate action from both software vendors and system administrators. The most effective immediate solution was to disable Java applet execution in web browsers or to upgrade to patched versions of the affected Java Runtime Environments and browsers. Microsoft released security updates for Internet Explorer that addressed the specific verifier issue, while Oracle and other Java vendors issued patches for their JDK and JRE implementations. Organizations should have implemented network-level controls to block potentially malicious applet content and updated their security policies to restrict Java applet execution to trusted sources only. The vulnerability highlighted the importance of maintaining up-to-date security patches and demonstrated the critical nature of proper code verification in security-critical components. Long-term mitigation included the gradual deprecation of Java applets in favor of more secure web technologies and the implementation of more robust sandboxing mechanisms that could prevent similar verification bypass exploits. System administrators should have conducted comprehensive vulnerability assessments to identify all systems running vulnerable Java versions and implemented monitoring for suspicious applet execution patterns that could indicate exploitation attempts.