CVE-2021-26730: Uncovering a Stack-Based Buffer Overflow Vulnerability in Lanner IAC-AST250A Firmware

A recent stack-based buffer overflow vulnerability has come to light in Lanner Electronics' IAC-AST250A firmware, a widely-used solution for remote management in servers and other appliances. This vulnerability has grabbed the attention of the cybersecurity community, as an attacker may exploit it to gain unauthorized access and execute arbitrary code on targeted systems. The vulnerability, tagged as CVE-2021-26730, affects the most recent standard firmware version 1.10. of the product. In this article, we will delve into the details of this security flaw, common exploitation techniques, and recommend ways to mitigate its potential impact.

Vulnerability Details

CVE-2021-26730 is a stack-based buffer overflow vulnerability that exists in a subfunction of the Login_handler_func function of spx_restservice. This issue arises from improper input validation and control, allowing an attacker to exploit vulnerable systems to execute arbitrary code with the same privileges as the server user, which is usually the root user. The primary target of such an attack would be systems running the IAC-AST250A firmware at version 1.10..

Code Snippet

The vulnerable code, as discovered in spx_restservice, is located within the subfunction of the Login_handler_func function. The stack-based buffer overflow can be triggered when an attacker sends a malformed input to the following segment of the code:

ssize_t Login_handler_func(sub_function_data, user_input) {
    ...
    char buffer[256];
    ...
    sscanf(user_input, "%s %s", buffer, buffer2);
    ...
}

As visible in the code snippet above, the buffer has a fixed size of 256 bytes. However, the absence of proper validation means that an attacker can easily exploit this code by injecting larger input values, thereby overwriting adjacent memory regions.

Exploitation

To exploit this vulnerability, an attacker has to craft malicious input that specifically targets the faulty code. The attacker can initiate this attack by sending a large input payload specifically designed to overwrite the memory region adjacent to the buffer. Once redirected to the attacker's desired location, the arbitrary code embedded in the input can piggyback on the Login_handler_func function to execute with root privileges.

Since the vulnerable function processes user credentials, an attacker with low-level access can potentially launch privilege escalation attacks to imitate a root user, further compromising the affected system.

Original References

For those seeking a deeper understanding of this vulnerability, the following is a list of helpful resources:

1. CVE Details: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-26730
2. Lanner Inc IAC-AST250A Firmware: https://www.lannerinc.com/products/embedded-box-pcs/automation-control/IAC-AST250A
3. NIST Vulnerability Database: https://nvd.nist.gov/vuln/detail/CVE-2021-26730

Mitigation

To safeguard affected systems from the potential risks of CVE-2021-26730, organizations can follow the recommendations below:

1. Keep your firmware up to date: Lanner Electronics is expected to address this vulnerability in future releases of their firmware. Ensure that systems using IAC-AST250A receive timely updates to minimize the window of exposure.

2. Perform access control audits: Regularly review user access levels and privileges to ensure that only necessary personnel have high-level access. Be mindful of privileged escalations among employees, as this can offer potential entry points for attackers.

3. Prioritize input validation and sanitizing: Review software components that rely on user inputs, particularly when handling sensitive information such as login credentials. Implement proper input validation methods and sanitize untrustworthy inputs before processing.

Conclusion

CVE-2021-26730 highlights the importance of cybersecurity vigilance and regular system audits, especially for products embedded in critical infrastructure components. By understanding the risks associated with this kind of vulnerability, organizations can take appropriate measures to safeguard their systems against potential exploitation.

Timeline

Published on: 10/24/2022 14:15:00 UTC
Last modified on: 10/24/2022 17:27:00 UTC