CVE-2002-2244 in Akfingerd
Summary
by MITRE
Akfingerd 0.5 and earlier versions allow local users to cause a denial of service (crash) via a .plan with a symlink to /dev/urandom or other device, then disconnecting while data is being transferred, which causes a SIGPIPE error that Akfingerd cannot handle.
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Analysis
by VulDB Data Team • 06/28/2021
The vulnerability identified as CVE-2002-2244 affects Akfingerd version 0.5 and earlier, representing a significant security flaw in the finger daemon implementation that can be exploited to cause a denial of service condition. This issue specifically targets the handling of symbolic links within the .plan file mechanism, which is commonly used by finger services to display user information. The vulnerability stems from inadequate error handling within the daemon's data transfer process, creating a scenario where malicious local users can manipulate the system's response to SIGPIPE signals.
The technical implementation of this vulnerability involves the creation of a symbolic link within the user's .plan file that points to sensitive system devices such as /dev/urandom or other device files. When the finger daemon attempts to read and transfer data from this symbolic link during a connection session, it encounters a situation where data transfer is interrupted while the daemon is actively reading from the device file. This interruption triggers a SIGPIPE signal, which the Akfingerd daemon fails to properly handle or catch, leading to an ungraceful termination of the service.
This vulnerability operates under the broader category of improper error handling within network services, which aligns with CWE-704 in the Common Weakness Enumeration classification system. The flaw demonstrates a classic example of how insufficient signal handling can lead to service disruption, particularly in daemon processes that manage multiple concurrent connections. The attack vector is specifically local, meaning that any user with access to the system can potentially exploit this weakness without requiring remote network access, making it particularly concerning for multi-user environments where privilege separation may not be adequate.
The operational impact of this vulnerability extends beyond simple service disruption, as it can potentially be used to systematically destabilize the finger service on a compromised system. The SIGPIPE error handling failure creates a predictable crash condition that can be repeatedly exploited to maintain service unavailability. This type of denial of service attack can be particularly damaging in environments where finger services are relied upon for user information access, system monitoring, or administrative purposes. The vulnerability also highlights the importance of proper resource management and signal handling in daemon processes, as the improper handling of device file access can lead to complete service failure.
Mitigation strategies for this vulnerability should focus on implementing proper error handling mechanisms within the Akfingerd daemon to gracefully manage SIGPIPE signals and other potential interruption conditions. System administrators should consider updating to newer versions of Akfingerd where this issue has been addressed, or implementing proper signal handling routines that prevent the daemon from crashing when encountering unexpected interruption conditions. Additionally, implementing proper file access controls and restricting symbolic link creation within user directories can help prevent exploitation of this specific vulnerability. The issue also underscores the need for comprehensive input validation and proper resource cleanup in network services, particularly those that handle user-provided data files such as .plan files. Organizations should also consider implementing monitoring for unusual service termination patterns that could indicate exploitation attempts. This vulnerability serves as a reminder of the critical importance of robust error handling in system services, particularly those that operate with elevated privileges and handle user data, as outlined in various cybersecurity frameworks including the ATT&CK matrix for service disruption techniques.