Skip to content

CVE-2017-12240 — The DHCP relay subsystem of Cisco IOS 12.2 through 15.6 and Cisco IOS XE Software…

Key facts

CVE-2017-12240 is a Critical (9.8) vulnerability: The DHCP relay subsystem of Cisco IOS 12.2 through 15.6 and Cisco IOS XE Software…. This entry ships a detection-only PoC and a Docker test lab. It is on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2022-03-03), confirming active exploitation in the wild.

Actively exploited — on the CISA KEV catalog

CVE-2017-12240 is listed on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2022-03-03), confirming exploitation in the wild. Federal remediation deadline: 2022-03-24. Prioritise patching and deploy the detection and prevention rules below.
CVE CVE-2017-12240
Severity Critical (9.8)
CISA KEV Actively exploited (added 2022-03-03)
Detection / prevention —
PoC poc.py
Source 2017/CVE-2017-12240/

Details

English | 한국어

Description

The DHCP relay subsystem of Cisco IOS 12.2 through 15.6 and Cisco IOS XE Software contains a vulnerability that could allow an unauthenticated, remote attacker to execute arbitrary code and gain full control of an affected system. The attacker could also cause an affected system to reload, resulting in a denial of service (DoS) condition. The vulnerability is due to a buffer overflow condition in the DHCP relay subsystem of the affected software. An attacker could exploit this vulnerability by sending a crafted DHCP Version 4 (DHCPv4) packet to an affected system. A successful exploit could allow the attacker to execute arbitrary code and gain full control of the affected system or cause the affected system to reload, resulting in a DoS condition. Cisco Bug IDs: CSCsm45390, CSCuw77959.

Vulnerability Details

Property Value
CVE ID CVE-2017-12240
CVSS Score 9.8

Proof of Concept

Download

# Download PoC script
curl -O https://raw.githubusercontent.com/fankh/vulnerability-poc/main/2017/CVE-2017-12240/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-2017-12240

# 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://www.securityfocus.com/bid/101034
  • http://www.securitytracker.com/id/1039445
  • https://quickview.cloudapps.cisco.com/quickview/bug/CSCsm45390
  • https://quickview.cloudapps.cisco.com/quickview/bug/CSCuw77959
  • https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170927-dhcp
  • http://www.securityfocus.com/bid/101034
  • http://www.securitytracker.com/id/1039445
  • https://quickview.cloudapps.cisco.com/quickview/bug/CSCsm45390
  • https://quickview.cloudapps.cisco.com/quickview/bug/CSCuw77959
  • https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170927-dhcp
  • https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2017-12240

Generated by PoC Generator on 2026-07-03T17:54:12.205976849

Frequently asked questions

What is CVE-2017-12240?

CVE-2017-12240 is a Critical (9.8) vulnerability: The DHCP relay subsystem of Cisco IOS 12.2 through 15.6 and Cisco IOS XE Software…. This entry ships a detection-only PoC and a Docker test lab. It is on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2022-03-03), confirming active exploitation in the wild.

How do I detect CVE-2017-12240?

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-2017-12240?

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-2017-12240 actively exploited?

Yes. CVE-2017-12240 is on the CISA Known Exploited Vulnerabilities (KEV) catalog, added 2022-03-03, which means it has been exploited in the wild. CISA set a federal remediation deadline of 2022-03-24. Prioritise patching and deploy the detection and prevention rules above.

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