CVE-2003-0896 in JVM
Summary
by MITRE
The loadClass method of the sun.applet.AppletClassLoader class in the Java Virtual Machine (JVM) in Sun SDK and JRE 1.4.1_03 and earlier allows remote attackers to bypass sandbox restrictions and execute arbitrary code via a loaded class name that contains "/" (slash) instead of "." (dot) characters, which bypasses a call to the Security Manager s checkPackageAccess method.
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Analysis
by VulDB Data Team • 12/18/2024
The vulnerability described in CVE-2003-0896 represents a critical security flaw in the Java Virtual Machine's class loading mechanism that fundamentally undermines the sandbox security model designed to protect users from malicious code execution. This issue affects Sun SDK and JRE versions 1.4.1_03 and earlier, where the loadClass method in the sun.applet.AppletClassLoader class contains a flaw that allows remote attackers to circumvent security restrictions. The vulnerability specifically exploits how the JVM handles class name resolution during the loading process, creating a pathway for attackers to execute arbitrary code that would normally be blocked by the security manager.
The technical flaw resides in the improper handling of class name separators within the loadClass method implementation. When a class name contains forward slash characters instead of the expected dot characters, the security manager's checkPackageAccess method fails to properly validate the class loading request. This occurs because the JVM's security validation logic does not adequately normalize or sanitize class name representations before performing access checks. The flaw enables attackers to construct malicious class names that bypass the intended security boundaries, effectively allowing unauthorized code execution within the restricted environment. This type of vulnerability falls under CWE-254, which addresses security weaknesses related to improper input validation and insufficient security checks.
The operational impact of this vulnerability is severe as it allows remote attackers to completely bypass the Java sandbox restrictions that are fundamental to preventing malicious code from accessing local resources or executing harmful operations. An attacker could potentially load malicious classes that have access to system resources, file systems, network capabilities, or other privileged operations that should be restricted to trusted code only. The vulnerability particularly affects applet execution environments where the security model relies on package access controls to prevent unauthorized behavior, making web-based Java applications susceptible to code injection attacks that could lead to complete system compromise.
Mitigation strategies for this vulnerability include immediate upgrading to patched versions of the Java Runtime Environment that address the class loading validation issue. Organizations should implement strict monitoring of class loading activities and network traffic to detect potential exploitation attempts. The security manager configuration should be reviewed to ensure proper enforcement of package access controls, and administrators should consider implementing additional security measures such as code signing verification and network segmentation. This vulnerability aligns with ATT&CK technique T1059.007, which covers the use of Java for code execution, and demonstrates how improper input handling can lead to privilege escalation through sandbox bypass mechanisms. The fix typically involves strengthening the validation logic in the class loader to properly normalize class name representations and ensure that all package access checks are performed consistently regardless of the character representation used in class names.