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CVE-2021-39144 — XStream is a simple library to serialize objects to XML and back again.

Key facts

CVE-2021-39144 is a High (8.5) vulnerability: XStream is a simple library to serialize objects to XML and back again.. This entry ships a detection-only PoC and a Docker test lab. It is on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2023-03-10), confirming active exploitation in the wild.

Actively exploited — on the CISA KEV catalog

CVE-2021-39144 is listed on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2023-03-10), confirming exploitation in the wild. Federal remediation deadline: 2023-03-31. Prioritise patching and deploy the detection and prevention rules below.
CVE CVE-2021-39144
Severity High (8.5)
CISA KEV Actively exploited (added 2023-03-10)
Detection / prevention —
PoC poc.py
Source 2021/CVE-2021-39144/

Details

English | 한국어

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.

Vulnerability Details

Property Value
CVE ID CVE-2021-39144
CVSS Score 8.5

Proof of Concept

Download

# Download PoC script
curl -O https://raw.githubusercontent.com/fankh/vulnerability-poc/main/2021/CVE-2021-39144/poc.py

Usage

# Run PoC against target
python3 poc.py --target <TARGET_URL>

# With authentication
python3 poc.py --target <TARGET_URL> --username <USER> --password <PASS>

⚠️ Warning: This PoC is for authorized security testing only. It uses detection-only techniques and does not exploit or damage target systems.

Test Lab

This repository includes a Docker-based test environment with both vulnerable and patched applications.

Quick Start

# Clone and navigate to CVE directory
cd CVE-2021-39144

# Start both applications
docker-compose up -d

# Run tests
./run-tests.sh    # Linux/Mac
./run-tests.ps1   # Windows PowerShell

Application Endpoints

Application URL Status
Vulnerable App http://localhost:8080 Shows vulnerability
Patched App http://localhost:8081 Demonstrates fix

Directory Structure

├── README.md           # English documentation
├── README_KO.md        # Korean documentation
├── poc.py              # PoC detection script
├── docker-compose.yml  # Container orchestration
├── run-tests.sh        # Linux/Mac test runner
├── run-tests.ps1       # Windows test runner
├── vulnerable-app/     # Vulnerable version
│   ├── app.py
│   ├── Dockerfile
│   └── requirements.txt
└── patched-app/        # Fixed version
    ├── app.py
    ├── Dockerfile
    └── requirements.txt

References

  • http://packetstormsecurity.com/files/169859/VMware-NSX-Manager-XStream-Unauthenticated-Remote-Code-Execution.html
  • https://github.com/x-stream/xstream/security/advisories/GHSA-j9h8-phrw-h4fh
  • https://lists.debian.org/debian-lts-announce/2021/09/msg00017.html
  • https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/22KVR6B5IZP3BGQ3HPWIO2FWWCKT3DHP/
  • https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PVPHZA7VW2RRSDCOIPP2W6O5ND254TU7/
  • https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QGXIU3YDPG6OGTDHMBLAFN7BPBERXREB/
  • https://security.netapp.com/advisory/ntap-20210923-0003/
  • https://www.debian.org/security/2021/dsa-5004
  • https://www.oracle.com/security-alerts/cpuapr2022.html
  • https://www.oracle.com/security-alerts/cpujan2022.html
  • https://www.oracle.com/security-alerts/cpujul2022.html
  • https://x-stream.github.io/CVE-2021-39144.html
  • http://packetstormsecurity.com/files/169859/VMware-NSX-Manager-XStream-Unauthenticated-Remote-Code-Execution.html
  • https://github.com/x-stream/xstream/security/advisories/GHSA-j9h8-phrw-h4fh
  • https://lists.debian.org/debian-lts-announce/2021/09/msg00017.html
  • https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/22KVR6B5IZP3BGQ3HPWIO2FWWCKT3DHP/
  • https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/PVPHZA7VW2RRSDCOIPP2W6O5ND254TU7/
  • https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/QGXIU3YDPG6OGTDHMBLAFN7BPBERXREB/
  • https://security.netapp.com/advisory/ntap-20210923-0003/
  • https://www.debian.org/security/2021/dsa-5004
  • https://www.oracle.com/security-alerts/cpuapr2022.html
  • https://www.oracle.com/security-alerts/cpujan2022.html
  • https://www.oracle.com/security-alerts/cpujul2022.html
  • https://x-stream.github.io/CVE-2021-39144.html
  • https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-39144

Generated by PoC Generator on 2026-07-30T09:57:44.207468259

Frequently asked questions

What is CVE-2021-39144?

CVE-2021-39144 is a High (8.5) vulnerability: XStream is a simple library to serialize objects to XML and back again.. This entry ships a detection-only PoC and a Docker test lab. It is on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2023-03-10), confirming active exploitation in the wild.

How do I detect CVE-2021-39144?

Run the detection-only PoC included with this entry against your Docker test lab to confirm whether a target is affected; pair it with your own IDS logging.

How do I block or mitigate CVE-2021-39144?

Upgrade to a fixed version per the vendor advisory; the NVD record lists the affected versions. Use the included PoC to verify your remediation.

Is CVE-2021-39144 actively exploited?

Yes. CVE-2021-39144 is on the CISA Known Exploited Vulnerabilities (KEV) catalog, added 2023-03-10, which means it has been exploited in the wild. CISA set a federal remediation deadline of 2023-03-31. Prioritise patching and deploy the detection and prevention rules above.

For authorized security testing and research only. See the full source and NVD record.