CVE-2002-0423 in Efingerd
Summary
by MITRE
Buffer overflow in efingerd 1.5 and earlier, and possibly up to 1.61, allows remote attackers to cause a denial of service and possibly execute arbitrary code via a finger request from an IP address with a long hostname that is obtained via a reverse DNS lookup.
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Analysis
by VulDB Data Team • 06/07/2018
The vulnerability identified as CVE-2002-0423 represents a critical buffer overflow flaw affecting efingerd versions 1.5 and earlier, with potential impact extending to version 1.61. This issue resides within the finger protocol implementation where the service performs reverse DNS lookups on incoming IP addresses to resolve hostnames. The flaw occurs when the system processes a finger request from an attacker-controlled IP address that contains an excessively long hostname, causing the buffer allocated for hostname storage to overflow. This class of vulnerability falls under CWE-121 which specifically addresses stack-based buffer overflow conditions, and it aligns with ATT&CK technique T1203 for legitimate program exploitation through buffer overflow mechanisms.
The technical exploitation of this vulnerability occurs when an attacker sends a finger request to the efingerd service from an IP address that has a reverse DNS entry containing an abnormally long hostname string. During processing, the service attempts to store this hostname in a fixed-size buffer without proper bounds checking, leading to memory corruption that can result in program termination or potentially arbitrary code execution. The buffer overflow specifically affects the hostname resolution component of the finger protocol implementation, where the service expects hostnames to be of reasonable length but does not validate or limit the size of incoming hostname data from reverse DNS lookups. This vulnerability is particularly dangerous because it can be exploited remotely without authentication requirements, making it a significant threat to network services that rely on finger protocol functionality.
The operational impact of CVE-2002-0423 extends beyond simple denial of service to potentially enabling remote code execution, depending on the system configuration and memory layout. When exploited successfully, the buffer overflow can corrupt program execution flow, allowing attackers to inject and execute malicious code with the privileges of the efingerd process. This could lead to complete system compromise, especially if the service runs with elevated privileges. Organizations running affected versions of efingerd face significant risk, particularly in environments where finger services are exposed to untrusted networks. The vulnerability also demonstrates poor input validation practices that are common in legacy network services, highlighting the need for robust bounds checking in all network-facing applications.
Mitigation strategies for CVE-2002-0423 should include immediate patching of efingerd to versions that address the buffer overflow vulnerability, typically through updates that implement proper bounds checking for hostname strings. System administrators should also consider disabling the finger service entirely if it is not required for operational purposes, as this eliminates the attack surface entirely. Network-level mitigations include implementing firewall rules to restrict access to finger service ports, typically port 79, and configuring reverse DNS lookup restrictions to prevent malicious hostname injection. Additionally, monitoring systems should be deployed to detect unusual hostname resolution patterns that might indicate exploitation attempts. Organizations should also implement regular vulnerability assessments to identify and remediate similar buffer overflow vulnerabilities in other legacy network services, following best practices outlined in industry standards such as the OWASP Top Ten and NIST guidelines for secure coding practices.