CVE-2014-8121 in C Library
Summary
by MITRE
DB_LOOKUP in nss_files/files-XXX.c in the Name Service Switch (NSS) in GNU C Library (aka glibc or libc6) 2.21 and earlier does not properly check if a file is open, which allows remote attackers to cause a denial of service (infinite loop) by performing a look-up on a database while iterating over it, which triggers the file pointer to be reset.
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Analysis
by VulDB Data Team • 04/12/2022
The vulnerability identified as CVE-2014-8121 resides within the Name Service Switch functionality of the GNU C Library, specifically in the DB_LOOKUP implementation within nss_files/files-XXX.c. This flaw affects glibc versions 2.21 and earlier, representing a critical security issue that undermines system stability through improper file handling mechanisms. The Name Service Switch serves as a crucial component in Unix-like operating systems, enabling applications to query various naming services including local files, network databases, and directory services through a unified interface. When a lookup operation is performed on a database while simultaneously iterating over it, the system encounters a problematic state where file pointer reset operations create conditions conducive to system instability.
The technical root cause of this vulnerability stems from inadequate validation of file open states within the NSS subsystem. During normal operation, when applications request name resolution services, the NSS mechanism processes these requests by consulting various data sources through configured lookup methods. The flaw manifests when a database lookup operation attempts to access a file that is already being processed in an iteration context. This creates a race condition where the file descriptor management becomes inconsistent, leading to scenarios where the file pointer gets reset inappropriately. The improper state management results in the system entering an infinite loop during lookup operations, as the reset file pointer causes the iteration process to continuously revisit the same data points without proper termination conditions.
The operational impact of this vulnerability extends beyond simple denial of service, as it can severely compromise system availability and resource utilization. Attackers exploiting this weakness can trigger sustained resource exhaustion through continuous loop operations, effectively consuming system CPU cycles and potentially causing legitimate services to become unresponsive. The vulnerability is particularly dangerous in server environments where NSS lookups are frequently performed, as the infinite loop can quickly escalate from a minor disruption to a complete system outage. Additionally, the nature of the flaw means that even a single malicious lookup request can cause cascading effects throughout the system, as the infinite loop consumes resources that other critical processes require for normal operation.
Mitigation strategies for CVE-2014-8121 should prioritize immediate patching of affected glibc versions to the latest stable releases containing the necessary fixes. System administrators should implement monitoring solutions to detect unusual CPU usage patterns that might indicate exploitation attempts, particularly focusing on NSS-related processes. Network segmentation and access controls should be strengthened to limit potential attack vectors that could leverage this vulnerability. The fix implemented in patched versions addresses the core file state management issue by ensuring proper validation of file open conditions before allowing lookup operations to proceed. This aligns with security best practices outlined in the CWE-367 principle of preventing command injection and improper file handling, while also addressing the ATT&CK technique of privilege escalation through system resource manipulation. Organizations should also conduct comprehensive vulnerability assessments to identify any other systems running affected glibc versions and ensure all network services that rely on NSS functionality are properly updated to prevent exploitation attempts.