GHSA-rmr5-cpv2-vgjf
HIGHDenial of Service by injecting highly recursive collections or maps in XStream
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
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 allocate 100% CPU time on the target system depending on CPU type or parallel execution of such a payload resulting in a denial of service only by manipulating the processed input stream.
Patches
XStream 1.4.19 monitors and accumulates the time it takes to add elements to collections and throws an exception if a set threshold is exceeded.
Workarounds
The attack uses the hash code implementation for collections and maps to force an exponential calculation time due to highly recursive structures with in the collection or map. Following types of the Java runtime are affected in Java versions available in December 2021:
- java.util.HashMap
- java.util.HashSet
- java.util.Hashtable
- java.util.LinkedHashMap
- java.util.LinkedHashSet
- java.util.Stack (older Java revisions only)
- java.util.Vector (older Java revisions only)
- Other third party collection implementations that use their element's hash code may also be affected
If your object graph does not use referenced elements at all, you may simply set the NO_REFERENCE mode:
XStream xstream = new XStream();
xstream.setMode(XStream.NO_REFERENCES);
If your object graph contains neither a Hashtable, HashMap nor a HashSet (or one of the linked variants of it) then you can use the security framework to deny the usage of these types:
XStream xstream = new XStream();
xstream.denyTypes(new Class[]{
java.util.HashMap.class, java.util.HashSet.class, java.util.Hashtable.class, java.util.LinkedHashMap.class, java.util.LinkedHashSet.class
});
Unfortunately these types are very common. If you only use HashMap or HashSet and your XML refers these only as default map or set, you may additionally change the default implementation of java.util.Map and java.util.Set at unmarshalling time::
xstream.addDefaultImplementation(java.util.TreeMap.class, java.util.Map.class);
xstream.addDefaultImplementation(java.util.TreeSet.class, java.util.Set.class);
However, this implies that your application does not care about the implementation of the map and all elements are comparable.
References
See full information about the nature of the vulnerability and the steps to reproduce it in XStream's documentation for CVE-2021-43859.
Credits
The vulnerability was discovered and reported by r00t4dm at Cloud-Penetrating Arrow Lab.
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 | 1.4.19 |
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 1.4.19 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-rmr5-cpv2-vgjf 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-rmr5-cpv2-vgjf 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-rmr5-cpv2-vgjf. 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-rmr5-cpv2-vgjf in your dependencies?
O3 detects GHSA-rmr5-cpv2-vgjf across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.