CVE-2021-21347 — xstream
CRITICALCVE-2021-21347 is a critical-severity (CVSS 9.8) Unrestricted File Upload vulnerability in com.thoughtworks.xstream:xstream. 1 public exploit reference exists, so weaponization risk is real. A fix is available for com.thoughtworks.xstream:xstream — see the affected versions and patch details below.
XStream is vulnerable to an Arbitrary Code Execution attack
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2021-21347.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2021-21347 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 385,386 CVEs with a current EPSS score, this one falls in the 10–50% band (highlighted). Counts from FIRST.org, log-scaled.
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 load and execute arbitrary code from a remote host only by manipulating the processed input stream. No user is affected, who followed the recommendation to setup XStream's security framework with a whitelist limited to the minimal required types.
Patches
If you rely on XStream's default blacklist of the Security Framework, you will have to use at least version 1.4.16.
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-2021-21347.
Credits
The vulnerability was discovered and reported by threedr3am.
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 | 1.4.16com.thoughtworks.xstream:xstream:1.4.16 |
Affected Products
activemqapachejmeterapachedebian linuxdebianfedorafedoraprojectoncommand insightnetappbanking enterprise default managementoracleResearch 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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update com.thoughtworks.xstream:xstream to 1.4.16 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21347 is resolved across your whole dependency graph.
Workarounds
Treat uploaded files as untrusted until proven otherwise: validate the actual content type rather than the supplied extension, store uploads outside the web root on a volume mounted without execute permission, and rename them to server-generated identifiers so an attacker cannot choose the path a request will later resolve.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
OpenShift Container Platform (OCP) delivers Jenkins LTS package with bundled XStream library. Due to JEP-200 [1] and JEP-228 [2] Jenkins projects, OCP Jenkins package is not affected by this flaw. [1] https://github.com/jenkinsci/jep/blob/master/jep/200/README.adoc [2]…
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Data Grid 8.2.0 | xstream | RHSA-2021:2139 |
| Red Hat Enterprise Linux 7 | xstream-0:1.3.1-13.el7_9 | RHSA-2021:1354 |
| Red Hat Fuse 7.10 | xstream | RHSA-2021:5134 |
| Red Hat Integration | see advisory | RHSA-2021:4918 |
| Red Hat Integration Camel Quarkus 2 | see advisory | RHSA-2021:4767 |
| RHDM 7.11.0 | xstream | RHSA-2021:2476 |
| RHPAM 7.11.0 | xstream | RHSA-2021:2475 |
Frequently Asked Questions
Is CVE-2021-21347 in your dependencies?
Find it across Maven, including transitive dependencies.