How severe is CVE-2021-21349?

CVE-2021-21349 has a CVSS score of 8.6/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-21349?

CVE-2021-21349 affects the following packages: com.thoughtworks.xstream:xstream (Maven). Ecosystems affected: Maven.

How do I fix CVE-2021-21349?

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-2021-21349 is resolved across your whole dependency graph.

How do I detect CVE-2021-21349 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-2021-21349 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-2021-21349 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-21349, 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-2021-21349?

CVE-2021-21349 has an EPSS (Exploit Prediction Scoring System) score of 46.8%, placing it in the 99th 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 warrants monitoring and prompt remediation.

What type of vulnerability is CVE-2021-21349?

CVE-2021-21349 is classified as Deserialization of Untrusted Data (CWE-502), Server-Side Request Forgery (SSRF) (CWE-918). 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-2021-21349 published, and has it been updated?

CVE-2021-21349 was published on March 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

HIGH severity

CVE-2021-21349 — xstream

HIGH

CVE-2021-21349 is a high-severity (CVSS 8.6) 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.

A Server-Side Forgery Request can be activated unmarshalling with XStream to access data streams from an arbitrary URL referencing a resource in an intranet or the local host

Also known asBIT-activemq-2021-21349GHSA-f6hm-88x3-mfjv

Published

Mar 23, 2021

Updated

Oct 9, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

1 known

Exploitation data as of Oct 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

46.8%probability of exploitation in next 30 days

High Risk0.00%

Lower risk than most CVEs99th percentile — riskier than 99% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2021-21349 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

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 request data from internal resources that are not publicly available 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-2021-21349.

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

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`com.thoughtworks.xstream:xstream`	all versions	1.4.16`com.thoughtworks.xstream:xstream:1.4.16`

Affected Products

17 products · 42 configurations

Application

activemqapache

< 5.15.14

2 versions

5.16.05.16.1

Application

jmeterapache

< 5.5

range

debian linuxdebian

3 versions

9.010.011.0

fedorafedoraproject

3 versions

333435

Application

oncommand insightnetapp

all

Application

banking enterprise default managementoracle

2 versions

2.10.02.12.0

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 Java library to serialize objects to XML and back again. In…

x-stream.github.ioNVDJul 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 1.4.16 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21349 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. [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 Fuse 7.10	`xstream`	RHSA-2021:5134
Red Hat Integration Camel Quarkus 2	see advisory	RHSA-2021:4767
RHDM 7.11.0	`xstream`	RHSA-2021:2476
RHINT Camel-K 1.6.4	see advisory	RHSA-2022:1029
RHPAM 7.11.0	`xstream`	RHSA-2021:2475

UbuntuHIGH

USN-4943-1Ubuntu USN-6978-1Ubuntu

Frequently Asked Questions

### Impact The vulnerability may allow a remote attacker to request data from internal resources that are not publicly available 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](https://x-stream.github.io/security.html#framework), you will have to use at least version 1.4.16. ### Workarounds See [workarounds](https://x-stream.github.io/security.html#workaround) for

O3 Security · Impact-Aware SCA

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