CVE-2002-2091 in Decfingerd
Summary
by MITRE
Format string vulnerability in Deception Finger Daemon, decfingerd, 0.7 may allow remote attackers to execute arbitrary code via the username of a finger request.
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Analysis
by VulDB Data Team • 08/30/2025
The vulnerability identified as CVE-2002-2091 represents a critical format string flaw in the Deception Finger Daemon software version 0.7, commonly known as decfingerd. This daemon serves as a finger service implementation that allows remote users to query user information on a system. The flaw exists in how the application processes incoming finger requests, specifically when handling the username parameter within the finger protocol. Format string vulnerabilities occur when application code uses user-supplied input directly in format functions like printf without proper validation or sanitization, creating opportunities for attackers to manipulate memory layout and execute arbitrary code.
The technical nature of this vulnerability stems from improper input handling within the decfingerd service, where the username portion of finger requests is directly passed to format string functions without adequate sanitization. This allows remote attackers to craft malicious finger requests containing format specifiers such as %x, %s, or %n that can be exploited to read from or write to memory locations. Attackers can leverage these format specifiers to perform stack reading, memory corruption, or even code execution by overwriting function pointers or return addresses. The vulnerability operates at the application layer and requires no special privileges to exploit, making it particularly dangerous as it can be triggered by any remote user connecting to the finger service.
The operational impact of this vulnerability extends beyond simple code execution, as it provides attackers with potential access to sensitive system information and could lead to complete system compromise. The finger protocol is commonly enabled on many systems for user information lookup, making this vulnerability widespread across affected deployments. Successful exploitation could allow attackers to read system memory, potentially exposing passwords, cryptographic keys, or other sensitive data, while also enabling arbitrary code execution that could result in privilege escalation or persistent access. The vulnerability affects systems where decfingerd is running and accepting finger requests, creating a significant attack surface for remote exploitation.
Mitigation strategies for CVE-2002-2091 should focus on immediate patching of the decfingerd software to version 0.7.1 or later, which contains the necessary fixes for the format string vulnerability. Organizations should disable the finger service entirely if it is not required for legitimate operations, as this eliminates the attack surface entirely. Network segmentation and firewall rules should be implemented to restrict access to finger service ports, typically port 79, to only trusted networks or systems. Additionally, monitoring for unusual finger service activity and implementing intrusion detection systems can help identify potential exploitation attempts. The vulnerability aligns with CWE-134 which specifically addresses format string vulnerabilities, and follows patterns commonly seen in the ATT&CK framework under technique T1059 for command and scripting interpreter and T1068 for exploit for privilege escalation. System administrators should also consider implementing input validation at the application level and ensuring proper error handling to prevent similar vulnerabilities in other services.