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CVE-2021-22555 — A heap out-of-bounds write affecting Linux since v2.6.19-rc1 was discovered in…

Key facts

CVE-2021-22555 is a High (8.3) vulnerability: A heap out-of-bounds write affecting Linux since v2.6.19-rc1 was discovered in…. This entry ships a detection-only PoC and a Docker test lab. It is on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2025-10-06), confirming active exploitation in the wild.

Actively exploited — on the CISA KEV catalog

CVE-2021-22555 is listed on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2025-10-06), confirming exploitation in the wild. Federal remediation deadline: 2025-10-27. Prioritise patching and deploy the detection and prevention rules below.
CVE CVE-2021-22555
Severity High (8.3)
CISA KEV Actively exploited (added 2025-10-06)
Detection / prevention —
PoC poc.py
Source 2021/CVE-2021-22555/

Details

English | 한국어

Description

A heap out-of-bounds write affecting Linux since v2.6.19-rc1 was discovered in net/netfilter/x_tables.c. This allows an attacker to gain privileges or cause a DoS (via heap memory corruption) through user name space

Vulnerability Details

Property Value
CVE ID CVE-2021-22555
Type RCE
CVSS Score 8.3

Proof of Concept

Download

# Download PoC script
curl -O https://raw.githubusercontent.com/fankh/vulnerability-poc/main/2021/CVE-2021-22555/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-2021-22555

# 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/163528/Linux-Kernel-Netfilter-Heap-Out-Of-Bounds-Write.html
  • http://packetstormsecurity.com/files/163878/Kernel-Live-Patch-Security-Notice-LSN-0080-1.html
  • http://packetstormsecurity.com/files/164155/Kernel-Live-Patch-Security-Notice-LSN-0081-1.html
  • http://packetstormsecurity.com/files/164437/Netfilter-x_tables-Heap-Out-Of-Bounds-Write-Privilege-Escalation.html
  • http://packetstormsecurity.com/files/165477/Kernel-Live-Patch-Security-Notice-LSN-0083-1.html
  • https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_tables.c?id=9fa492cdc160cd27ce1046cb36f47d3b2b1efa21
  • https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_tables.c?id=b29c457a6511435960115c0f548c4360d5f4801d
  • https://github.com/google/security-research/security/advisories/GHSA-xxx5-8mvq-3528
  • https://security.netapp.com/advisory/ntap-20210805-0010/
  • http://packetstormsecurity.com/files/163528/Linux-Kernel-Netfilter-Heap-Out-Of-Bounds-Write.html
  • http://packetstormsecurity.com/files/163878/Kernel-Live-Patch-Security-Notice-LSN-0080-1.html
  • http://packetstormsecurity.com/files/164155/Kernel-Live-Patch-Security-Notice-LSN-0081-1.html
  • http://packetstormsecurity.com/files/164437/Netfilter-x_tables-Heap-Out-Of-Bounds-Write-Privilege-Escalation.html
  • http://packetstormsecurity.com/files/165477/Kernel-Live-Patch-Security-Notice-LSN-0083-1.html
  • https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_tables.c?id=9fa492cdc160cd27ce1046cb36f47d3b2b1efa21
  • https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/netfilter/x_tables.c?id=b29c457a6511435960115c0f548c4360d5f4801d
  • https://github.com/google/security-research/security/advisories/GHSA-xxx5-8mvq-3528
  • https://security.netapp.com/advisory/ntap-20210805-0010/
  • https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-22555

Generated by PoC Generator on 2026-07-12T08:48:44.782610185

Frequently asked questions

What is CVE-2021-22555?

CVE-2021-22555 is a High (8.3) vulnerability: A heap out-of-bounds write affecting Linux since v2.6.19-rc1 was discovered in…. This entry ships a detection-only PoC and a Docker test lab. It is on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2025-10-06), confirming active exploitation in the wild.

How do I detect CVE-2021-22555?

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-2021-22555?

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-2021-22555 actively exploited?

Yes. CVE-2021-22555 is on the CISA Known Exploited Vulnerabilities (KEV) catalog, added 2025-10-06, which means it has been exploited in the wild. CISA set a federal remediation deadline of 2025-10-27. Prioritise patching and deploy the detection and prevention rules above.

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