CVE-2024-33601: GNU Glibc nscd Denial of Service Flaw

CVE-2024-33601 Overview

CVE-2024-33601 is a denial of service vulnerability affecting the Name Service Cache Daemon (nscd) component of the GNU C Library (glibc). The vulnerability exists in the netgroup cache functionality, where the use of xmalloc or xrealloc memory allocation functions can cause the nscd process to terminate unexpectedly when memory allocation fails. This results in a denial of service condition for all clients relying on the name service cache.

The flaw was introduced in glibc version 2.15 when the netgroup cache feature was added to nscd. This vulnerability specifically affects the nscd binary and can be triggered remotely without requiring authentication or user interaction.

Critical Impact

Remote attackers can cause the nscd daemon to crash by triggering memory allocation failures, leading to denial of service for all clients dependent on name service caching functionality.

Affected Products

• GNU glibc (versions 2.15 and later until patched)
• Debian Linux 10.0
• NetApp H-Series Storage Systems (H300s, H500s, H700s, H410s, H410c, H610c, H615c, H610s)
• NetApp HCI Bootstrap OS and Compute Nodes

Discovery Timeline

• May 6, 2024 - CVE-2024-33601 published to NVD
• August 1, 2025 - Last updated in NVD database

Technical Details for CVE-2024-33601

Vulnerability Analysis

This denial of service vulnerability stems from improper handling of memory allocation failures in the nscd netgroup cache implementation. The nscd daemon is responsible for caching name service lookups (such as passwd, group, and netgroup data) to improve system performance and reduce network traffic.

The vulnerability is classified under CWE-617 (Reachable Assertion), which indicates that the application contains an assertion that can be triggered by a remote attacker. In this case, the xmalloc and xrealloc functions used in the netgroup cache code do not handle allocation failures gracefully—instead, they terminate the entire nscd process when memory cannot be allocated.

An attacker can exploit this vulnerability over the network without requiring any privileges or user interaction. By forcing memory pressure conditions or crafting requests that trigger large allocations, an attacker can cause the memory allocation to fail and subsequently crash the nscd daemon.

Root Cause

The root cause is the use of xmalloc and xrealloc functions in the netgroup cache code path. These functions are designed to abort the program on allocation failure rather than returning NULL and allowing the caller to handle the error gracefully. When the netgroup cache was added in glibc 2.15, these functions were used without implementing proper fallback mechanisms for memory exhaustion scenarios.

The appropriate fix involves replacing these aborting allocation functions with their non-aborting counterparts (malloc/realloc) and implementing proper error handling to ensure the daemon can recover from transient memory pressure without terminating.

Attack Vector

The attack vector is network-based, allowing remote exploitation. An attacker can target systems running nscd by:

1. Sending a high volume of netgroup lookup requests to exhaust system memory
2. Crafting requests that result in large memory allocations within the netgroup cache
3. Timing attacks during periods of high system memory pressure

When the memory allocation fails during netgroup cache operations, the xmalloc or xrealloc function calls abort(), immediately terminating the nscd process. This affects all clients relying on nscd for name service caching, potentially impacting authentication, authorization, and other name-resolution-dependent operations across the system.

Detection Methods for CVE-2024-33601

Indicators of Compromise

• Unexpected termination or restart events for the nscd daemon service
• Core dumps generated by nscd with abort signals (SIGABRT)
• Repeated nscd service failures in system logs
• Memory allocation errors in nscd-related log entries

Detection Strategies

• Monitor system logs for nscd crash events using journalctl -u nscd or examining /var/log/syslog
• Configure process monitoring to alert on nscd daemon termination
• Implement memory usage monitoring for nscd process to detect unusual allocation patterns
• Deploy file integrity monitoring on nscd binary to detect unauthorized modifications

Monitoring Recommendations

• Enable core dump collection for nscd to capture crash forensics
• Set up automated alerting for nscd service state changes
• Monitor network traffic patterns to nscd port for anomalous request volumes
• Implement resource usage dashboards tracking nscd memory consumption trends

How to Mitigate CVE-2024-33601

Immediate Actions Required

• Update glibc to the latest patched version from your distribution vendor
• If patching is not immediately possible, consider disabling netgroup caching in nscd configuration
• Implement service restart automation for nscd to minimize downtime impact
• Review and apply available security advisories from GNU, Debian, and NetApp

Patch Information

Security patches addressing this vulnerability have been released by multiple vendors. Refer to the following resources for patch details:

• glibc Security Advisory GLIBC-SA-2024-0007 - Official glibc advisory and patch information
• Debian LTS Security Notice - Debian-specific patches and update instructions
• NetApp Security Advisory - NetApp product-specific guidance
• Openwall OSS Security Announcement - Community security discussion

Workarounds

• Disable netgroup caching by setting enable-cache netgroup no in /etc/nscd.conf
• Implement process supervision with automatic restart using systemd or similar tools
• Configure resource limits for nscd to prevent memory exhaustion scenarios
• Consider using alternative name service caching solutions such as sssd where applicable

# Disable netgroup cache in nscd.conf
echo "enable-cache netgroup no" >> /etc/nscd.conf
# Restart nscd to apply configuration
systemctl restart nscd
# Verify nscd status
systemctl status nscd