XStream is vulnerable to an Arbitrary Code Execution attack

Vulnerability

Overview

XStream, a Java library for serializing objects to XML and back, is vulnerable to arbitrary code execution in all versions up to and including 1.4.15. The root cause is that XStream reconstructs objects from XML based on type information embedded in the serialized data. An attacker can inject malicious type references that cause XStream to load and execute arbitrary code from a remote host [1][4].

Exploitation

The attack requires only that the attacker can supply a crafted XML input stream to an XStream instance that has not been properly configured with a security framework whitelist. The exploit uses a chain of Java objects (e.g., javax.naming.ldap.Rdn$RdnEntry, javax.swing.MultiUIDefaults, and sun.swing.SwingLazyValue) to trigger a remote lookup via JNDI, ultimately executing attacker-supplied code [4]. No authentication is needed, and the vulnerability can be triggered through any deserialization endpoint that accepts XStream-formatted data.

Impact

A successful exploit leads to remote code execution in the context of the vulnerable application. The attacker can perform any action that the application is allowed to do, including accessing private data, deleting files, or executing system commands [2][3]. Due to the severity, this CVE carries a high CVSS score (9.8 CRITICAL) [3].

Mitigation

The vulnerability is fixed in XStream version 1.4.16. Users are strongly advised to upgrade. As a workaround, users who have configured XStream's security framework with a whitelist of permitted types are not affected [2][4]. The default blacklist-based security is insufficient, and upgrading is the recommended course of action.