CVE-2012-4436 in fwknop
Summary
by MITRE
Buffer overflow in the run_last_args function in client/fwknop.c in fwknop before 2.0.3, when processing --last, might allow local users to cause a denial of service (client crash) and possibly execute arbitrary code via many .fwknop.run arguments.
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Analysis
by VulDB Data Team • 12/19/2021
The vulnerability identified as CVE-2012-4436 represents a critical buffer overflow flaw within the fwknop client application, specifically affecting versions prior to 2.0.3. This issue resides in the run_last_args function located within the client/fwknop.c source file, where improper input validation and memory management creates a pathway for malicious exploitation. The vulnerability becomes particularly dangerous when the fwknop client processes the --last command line argument, which is designed to retrieve and display previously processed Single Packet Authorization requests. The buffer overflow occurs due to inadequate bounds checking when handling multiple .fwknop.run arguments, creating a scenario where attacker-controlled input can overwrite adjacent memory regions beyond the allocated buffer space.
The technical nature of this vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and represents a classic example of improper input validation that can lead to arbitrary code execution. When local users provide numerous .fwknop.run arguments to the fwknop client, the run_last_args function fails to properly validate the number and size of these arguments before processing them. This allows attackers to overflow the allocated buffer and potentially overwrite critical memory segments including return addresses, function pointers, or other control data structures. The vulnerability's exploitation potential extends beyond simple denial of service to include arbitrary code execution, making it particularly concerning for systems where local privilege escalation might be possible.
The operational impact of this vulnerability is significant for any system running fwknop client versions below 2.0.3, particularly in environments where multiple users have access to the system or where the application might be executed with elevated privileges. A successful exploitation could result in complete system compromise through privilege escalation, as attackers could potentially inject and execute malicious code within the context of the fwknop client process. The vulnerability affects not only the immediate denial of service scenario but also creates a potential attack vector for persistent system compromise. Organizations relying on fwknop for network access control and single packet authorization would face increased risk of unauthorized access if this vulnerability remains unpatched, as attackers could leverage the buffer overflow to gain elevated privileges and potentially establish backdoors within the network infrastructure.
The mitigation strategy for CVE-2012-4436 requires immediate deployment of the official fwknop 2.0.3 patch or later versions that contain the necessary buffer overflow protections and input validation improvements. System administrators should conduct comprehensive vulnerability assessments to identify all instances of the vulnerable fwknop client versions within their infrastructure and ensure proper patch management protocols are followed. Additionally, implementing runtime protections such as stack canaries, address space layout randomization, and non-executable stack segments can provide defense-in-depth measures against potential exploitation attempts. Organizations should also consider monitoring for suspicious command line argument patterns that might indicate attempted exploitation of this vulnerability. The ATT&CK framework categorizes this vulnerability under privilege escalation and execution techniques, specifically targeting the use of local vulnerabilities to gain elevated system privileges. Regular security audits and penetration testing should include verification of proper input validation mechanisms within client applications to prevent similar buffer overflow conditions from being introduced in future development cycles.