CVE-2006-7254 in C Library
Summary
by MITRE
The nscd daemon in the GNU C Library (glibc) before version 2.5 does not close incoming client sockets if they cannot be handled by the daemon, allowing local users to carry out a denial of service attack on the daemon.
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Analysis
by VulDB Data Team • 08/28/2023
The nscd daemon in glibc versions prior to 2.5 contains a critical resource management flaw that enables local attackers to exhaust system socket file descriptors through a denial of service attack. This vulnerability resides in the daemon's handling of client connections where it fails to properly close socket descriptors when encountering malformed or unprocessable client requests. The flaw represents a classic resource leak scenario where the daemon maintains open socket connections indefinitely, consuming available file descriptor resources that are essential for normal system operation.
This vulnerability directly maps to CWE-404, which describes improper resource cleanup or release, and specifically manifests as a failure to close file descriptors in the nscd service. The technical implementation involves the daemon's accept loop where it accepts incoming client connections but does not properly handle error conditions during client request processing. When the daemon cannot process a client request due to malformed input or other processing errors, it leaves the socket connection open instead of closing it, leading to progressive resource exhaustion.
The operational impact of this vulnerability is significant for systems relying on nscd for name service caching, as local users can systematically consume all available socket file descriptors and cause the daemon to become unresponsive. This creates a persistent denial of service condition where legitimate client requests cannot be processed due to the daemon's inability to accept new connections. The attack is particularly effective because it requires minimal privileges and can be executed repeatedly to maintain the resource exhaustion state, making it a reliable vector for service disruption.
From an attack perspective, this vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks through resource exhaustion. The attack pattern involves establishing multiple client connections to the nscd daemon and then failing to properly process them, causing the daemon to maintain open socket connections indefinitely. The most effective mitigation strategy involves upgrading to glibc version 2.5 or later where the socket cleanup logic has been corrected to properly close all client connections regardless of processing success or failure. System administrators should also implement monitoring for unusual socket connection patterns and consider implementing connection limits to prevent rapid resource exhaustion. Additionally, deploying proper process monitoring and automatic restart mechanisms can help recover from successful attacks while maintaining service availability.