GHSA-mw36-7c6c-q4q2 is a high-severity (CVSS 8) OS Command Injection vulnerability in com.thoughtworks.xstream:xstream. 5 public exploit references exist, so weaponization risk is real. O3 Security confirms whether GHSA-mw36-7c6c-q4q2 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
XStream can be used for Remote Code Execution
Real-World Exposure
com.thoughtworks.xstream:xstreamReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
Description
Impact
The vulnerability may allow a remote attacker to run arbitrary shell commands only by manipulating the processed input stream.
Patches
If you rely on XStream's default blacklist of the Security Framework, you will have to use at least version 1.4.14.
Workarounds
No user is affected, who followed the recommendation to setup XStream's Security Framework with a whitelist! Anyone relying on XStream's default blacklist can immediately switch to a whilelist for the allowed types to avoid the vulnerability.
Users of XStream 1.4.13 or below who still want to use XStream default blacklist can use a workaround depending on their version in use.
Users of XStream 1.4.13 can simply add two lines to XStream's setup code:
xstream.denyTypes(new String[]{ "javax.imageio.ImageIO$ContainsFilter" });
xstream.denyTypes(new Class[]{ java.lang.ProcessBuilder.class });
Users of XStream 1.4.12 to 1.4.7 who want to use XStream with a black list will have to setup such a list from scratch and deny at least the following types: javax.imageio.ImageIO$ContainsFilter, java.beans.EventHandler, java.lang.ProcessBuilder, java.lang.Void and void.
xstream.denyTypes(new String[]{ "javax.imageio.ImageIO$ContainsFilter" });
xstream.denyTypes(new Class[]{ java.lang.ProcessBuilder.class, java.beans.EventHandler.class, java.lang.ProcessBuilder.class, java.lang.Void.class, void.class });
Users of XStream 1.4.6 or below can register an own converter to prevent the unmarshalling of the currently know critical types of the Java runtime. It is in fact an updated version of the workaround for CVE-2013-7285:
xstream.registerConverter(new Converter() {
public boolean canConvert(Class type) {
return type != null && (type == java.beans.EventHandler.class || type == java.lang.ProcessBuilder.class || type == java.lang.Void.class || void.class || type.getName().equals("javax.imageio.ImageIO$ContainsFilter") || Proxy.isProxy(type));
}
public Object unmarshal(HierarchicalStreamReader reader, UnmarshallingContext context) {
throw new ConversionException("Unsupported type due to security reasons.");
}
public void marshal(Object source, HierarchicalStreamWriter writer, MarshallingContext context) {
throw new ConversionException("Unsupported type due to security reasons.");
}
}, XStream.PRIORITY_LOW);
Credits
Chen L found and reported the issue to XStream and provided the required information to reproduce it. He was supported by Zhihong Tian and Hui Lu, both from Guangzhou University.
References
See full information about the nature of the vulnerability and the steps to reproduce it in XStream's documentation for CVE-2020-26217.
For more information
If you have any questions or comments about this advisory:
- Open an issue in XStream
- Contact us at XStream Google Group
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | com.thoughtworks.xstream:xstream | all versions | 1.4.14-java7 |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for com.thoughtworks.xstream:xstream. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update com.thoughtworks.xstream:xstream to 1.4.14-java7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-mw36-7c6c-q4q2 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-mw36-7c6c-q4q2 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-mw36-7c6c-q4q2. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-mw36-7c6c-q4q2 in your dependencies?
O3 detects GHSA-mw36-7c6c-q4q2 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.