How severe is CVE-2021-39140?

CVE-2021-39140 has a CVSS score of 6.3/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-39140?

CVE-2021-39140 affects the following packages: com.thoughtworks.xstream:xstream (Maven). Ecosystems affected: Maven.

How do I fix CVE-2021-39140?

Update com.thoughtworks.xstream:xstream to 1.4.18 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-39140 is resolved across your whole dependency graph.

How do I detect CVE-2021-39140 in my Maven dependencies?

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.

How do I mitigate CVE-2021-39140 if there is no patch (or I can't update yet)?

Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade.

Is CVE-2021-39140 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-39140, including 1 in-the-wild exploitation 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-2021-39140?

CVE-2021-39140 has an EPSS (Exploit Prediction Scoring System) score of 5.9%, placing it in the 93th 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. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-39140?

CVE-2021-39140 is classified as Deserialization of Untrusted Data (CWE-502), CWE-835 (CWE-835). 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.

When was CVE-2021-39140 published, and has it been updated?

CVE-2021-39140 was published on August 23, 2021 and was last updated on October 9, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

☕

☕ Maven

Not in CISA KEV

MEDIUM severity

CVE-2021-39140 — xstream

MEDIUM

CVE-2021-39140 is a medium-severity (CVSS 6.3) Deserialization of Untrusted Data 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 can cause a Denial of Service

Also known asGHSA-6wf9-jmg9-vxcc

Published

Aug 23, 2021

Updated

Oct 9, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

1 known

Exploitation data as of Oct 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

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.
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-2021-39140.

EPSS Exploitation Probability

via FIRST.org ↗

5.9%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs93th percentile — riskier than 93% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2021-39140 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

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

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. No user is affected, who followed the recommendation to setup XStream's security framework with a whitelist limited to the minimal required types.

Patches

XStream 1.4.18 uses no longer a blacklist by default, since it cannot be secured for general purpose.

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-2021-39140.

Credits

The vulnerability was discovered and reported by Lai Han of nsfocus security team.

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

1 total 1 fixed

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

Affected Products

15 products · 36 configurations

debian linuxdebian

3 versions

9.010.011.0

fedorafedoraproject

3 versions

333435

Application

snapmanagernetapp

all

Application

business activity monitoringoracle

1 version

12.2.1.4.0

Application

commerce guided searchoracle

1 version

11.3.2

Application

communications billing and revenue management elastic charging engineoracle

2 versions

11.312.0

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.

XStream is a simple library to serialize objects to XML and back again. …

x-stream.github.ioNVDAug 2021

Detection & mitigation playbook

Open-source dependency

Detect
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 1.4.18 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-39140 is resolved across your whole dependency graph.
Workarounds
Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade.

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.

Red HatModerate

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. This version of XStream library will be delivered in the future Jenkins releases. [1]…

Product	Fixed in	Advisory
Red Hat Data Grid 8.3.0	`xstream`	RHSA-2022:0520
Red Hat Enterprise Linux 7	`xstream-0:1.3.1-16.el7_9`	RHSA-2021:3956
Red Hat Integration	`xstream`	RHSA-2021:4918
Red Hat Integration Camel Quarkus 2	see advisory	RHSA-2021:4767
RHDM 7.12.0	`xstream`	RHSA-2022:0297
RHPAM 7.12.0	`xstream`	RHSA-2022:0296

UbuntuMEDIUM

USN-5946-1Ubuntu

Frequently Asked Questions

### 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. No user is affected, who followed the recommendation to setup XStream's security framework with a whitelist limited to the minimal required types. ### Patches XStream 1.4.18 uses no longer a blacklist by default, since it cannot be secured for general purpose. ### Workarounds See [workarounds](https://x-stream.github.io/security.html#workaround) fo