Summary
XStream is vulnerable to an Arbitrary File Deletion on the local host when unmarshalling as long as the executing process has sufficient rights
Workarounds
See workarounds for the different versions covering all CVEs.
References
See full information about the nature of the vulnerability and the steps to reproduce it in XStream's documentation for CVE-2021-21343.
Credits
钟潦贵 (Liaogui Zhong) found and reported the issue to XStream and provided the required information to reproduce it.
For more information
If you have any questions or comments about this advisory:
- Open an issue in XStream
- Contact us at XStream Google Group
Impact
The processed stream at unmarshalling time contains type information to recreate the formerly written objects. XStream creates therefore new instances based on these type information. An attacker can manipulate the processed input stream and replace or inject objects, that result in the deletion of a file on the local host. No user is affected, who followed the recommendation to setup XStream's security framework with a whitelist limited to the minimal required types.
Untrusted serialized data is processed by a deserializer that can instantiate arbitrary objects or execute code as a side effect. Typical impact: arbitrary code execution or logic abuse.
CVE-2021-21343 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.4.16); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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If you rely on XStream's default blacklist of the Security Framework, you will have to use at least version 1.4.16.
Frequently Asked Questions
- What is CVE-2021-21343? CVE-2021-21343 is a medium-severity insecure deserialization vulnerability in com.thoughtworks.xstream:xstream (maven), affecting versions < 1.4.16. It is fixed in 1.4.16. Untrusted serialized data is processed by a deserializer that can instantiate arbitrary objects or execute code as a side effect.
- How severe is CVE-2021-21343? CVE-2021-21343 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of com.thoughtworks.xstream:xstream are affected by CVE-2021-21343? com.thoughtworks.xstream:xstream (maven) versions < 1.4.16 is affected.
- Is there a fix for CVE-2021-21343? Yes. CVE-2021-21343 is fixed in 1.4.16. Upgrade to this version or later.
- Is CVE-2021-21343 exploitable, and should I be worried? Whether CVE-2021-21343 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2021-21343 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2021-21343? Upgrade
com.thoughtworks.xstream:xstreamto 1.4.16 or later.