CVE-2021-39149: XStream Arbitrary Code Execution Vulnerability
Summary
CVE-2021-39149: XStream is vulnerable to an Arbitrary Code Execution attack. Affects com.thoughtworks.xstream:xstream versions < 1.4.18. Fixed in 1.4.18. How to fix ↓
Also tracked for
- libxstream-java · Debian:11
The same CVE-2021-39149 is tracked separately for each ecosystem and vendor. Its fix information is the same; the package and affected versions differ.
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Background
XStream is an open-source Java library that allows for the serialization and deserialization of Java objects to XML and back. It provides a simple API for converting Java objects to XML and vice versa. XStream is widely used in various applications and frameworks for data persistence and communication. However, it is vulnerable to an Arbitrary Code Execution attack, which can allow a remote attacker to load and execute arbitrary code from a remote host by manipulating the processed input stream.
Vulnerability Detail
The vulnerability in XStream arises from the lack of proper input validation and filtering during the deserialization process. By crafting a malicious XML payload, an attacker can exploit this vulnerability to execute arbitrary code on the target system. This can lead to various consequences, including remote code execution, data theft, and unauthorized access to sensitive information. The impact of this vulnerability can be mitigated by following the recommended security practices, such as setting up XStream's security framework with a whitelist limited to the minimal required types.
How To Fix
Latest published version: 1.4.21 as of 22 Oct 2026
Upgrading to it may include breaking changes; the version below is the minimum fixed release for this vulnerability.
If you need the minimum change
1.4.18
This is the first release that contains the fix.
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Workaround
If updating to the latest version of XStream is not feasible, alternative workarounds are available. These workarounds are specific to different versions and can be found in the XStream documentation for CVE-2021-39149. Implementing the recommended workarounds can help mitigate the vulnerability until a proper update can be applied.
Conclusion
The CVE-2021-39149 vulnerability in XStream exposes systems to the risk of arbitrary code execution. It is crucial to update XStream to version 1.4.18 or later to mitigate this vulnerability. If updating is not immediately possible, implementing the recommended workarounds can provide temporary protection. For further support and assistance in vulnerability remediation, please contact DevNack.com.
See every vulnerability recorded for com.thoughtworks.xstream:xstream →
FAQ
XStream is an open-source Java library used for serialization and deserialization of Java objects to XML and vice versa. It provides a convenient API for converting Java objects to XML and back.
The vulnerability allows a remote attacker to execute arbitrary code on the target system by manipulating the input stream. This can lead to remote code execution, data theft, and unauthorized access to sensitive information.
To fix this vulnerability, it is recommended to update XStream to version 1.4.18 or later. This update addresses the vulnerability and reduces the risk of arbitrary code execution.
Yes, if updating to the latest version is not feasible, XStream provides specific workarounds for different versions. These workarounds can be implemented to mitigate the vulnerability until a proper update can be applied.
The vulnerability was discovered and reported by Lai Han of the NSFOCUS security team. They provided the necessary information to reproduce the issue and worked with XStream to address the vulnerability.
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