How severe is CVE-2021-39144?

CVE-2021-39144 has a CVSS score of 8.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-39144?

CVE-2021-39144 affects the following packages: com.thoughtworks.xstream:xstream (Maven). Ecosystems affected: Maven.

How do I fix CVE-2021-39144?

Update com.thoughtworks.xstream:xstream to version 1.4.18 or later. Run your dependency manager's update command and verify no transitive dependencies pin the vulnerable version. Use O3 Security's SCA scanner to confirm the fix is applied across your entire dependency tree.

Is CVE-2021-39144 actively exploited in the wild?

Yes. There are 6 known exploit references for CVE-2021-39144, including 6 in-the-wild exploitations observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-39144?

CVE-2021-39144 has an EPSS (Exploit Prediction Scoring System) score of 94.3%, placing it in the 100th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. A score above 50% indicates significantly elevated exploitation risk — immediate patching is strongly recommended.

Is CVE-2021-39144 in the CISA Known Exploited Vulnerabilities catalog?

Yes. CVE-2021-39144 (XStream Remote Code Execution Vulnerability) was added to CISA's Known Exploited Vulnerabilities (KEV) catalog on 2023-03-10. CISA required all US federal civilian agencies to remediate this vulnerability by 2023-03-31. The required action was: Apply updates per vendor instructions. Being listed in the KEV catalog is the strongest possible confirmation of active exploitation — treat this as a critical priority.

What type of vulnerability is CVE-2021-39144?

CVE-2021-39144 is classified as Code Injection (CWE-94), Deserialization of Untrusted Data (CWE-502), Missing Authentication (CWE-306). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

Is there exploit tooling available for CVE-2021-39144?

A Nuclei detection template exists for CVE-2021-39144, meaning automated scanners can fingerprint it. Public exploit tooling significantly increases real-world risk — prioritize patching and ensure detection coverage. Exploit tooling should only ever be used in isolated, authorized testing environments.

When was CVE-2021-39144 published, and has it been updated?

CVE-2021-39144 was published on August 23, 2021 and was last updated on April 16, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CISA KEV·Added 2023-03-10 — agencies required to remediate by 2023-03-31

☕ Maven

CVE-2021-39144

HIGH

XStream is vulnerable to a Remote Command Execution attack

Also known asGHSA-j9h8-phrw-h4fh

Published

Aug 23, 2021

Updated

Apr 16, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

6 known

EPSS Exploitation Probability

via FIRST.org ↗

94.3%probability of exploitation in next 30 days

Very High Risk100th percentile0.00%

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

1 pkg affected

☕com.thoughtworks.xstream:xstream

Real-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

XStream is a simple library to serialize objects to XML and back again. In affected versions this vulnerability may allow a remote attacker has sufficient rights to execute commands of the 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. XStream 1.4.18 uses no longer a blacklist by default, since it cannot be secured for general purpose.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`com.thoughtworks.xstream:xstream`	all versions	1.4.18

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.