CVE-2023-4813: GNU Glibc Use-After-Free Vulnerability

CVE-2023-4813 Overview

A use-after-free vulnerability has been identified in the GNU C Library (glibc), specifically within the gaih_inet function. Under uncommon circumstances, this function may reference memory that has already been freed, leading to an application crash. This issue is only exploitable when the getaddrinfo function is called and the hosts database in /etc/nsswitch.conf is configured with SUCCESS=continue or SUCCESS=merge options.

Critical Impact
Applications relying on glibc's name resolution functionality may experience denial of service conditions when specific nsswitch.conf configurations are present, potentially affecting service availability on affected Linux systems.

Affected Products

GNU glibc
Red Hat Enterprise Linux 8.0 and 9.0
Red Hat Enterprise Linux EUS 8.8 and 9.2
Red Hat Enterprise Linux for IBM z Systems
Red Hat Enterprise Linux for Power (little endian)
Red Hat Enterprise Linux Server AUS and TUS
Fedora 38
NetApp Active IQ Unified Manager
NetApp H-Series Storage Systems (H300S, H500S, H700S, H410S, H410C)

Discovery Timeline

September 12, 2023 - CVE-2023-4813 published to NVD
September 26, 2025 - Last updated in NVD database

Technical Details for CVE-2023-4813

Vulnerability Analysis

This vulnerability is classified as CWE-416 (Use After Free). The flaw exists in the gaih_inet function within glibc, which handles address information retrieval for network operations. When the getaddrinfo function is invoked and the system's /etc/nsswitch.conf file has specific non-default configurations for the hosts database (specifically SUCCESS=continue or SUCCESS=merge), the function may attempt to access memory that has already been deallocated.

The use-after-free condition occurs during the name resolution process, where the function references freed memory structures. While this vulnerability requires specific configuration conditions to be triggered, systems running with these nsswitch.conf settings are susceptible to exploitation. The primary impact is denial of service through application crashes, as the vulnerability does not appear to allow for arbitrary code execution or data exfiltration.

Root Cause

The root cause is improper memory management within the gaih_inet function in glibc. When processing address information with specific nsswitch.conf configurations that allow continuation after successful lookups (SUCCESS=continue) or merging of results (SUCCESS=merge), the function fails to properly track memory allocation states. This results in a dangling pointer scenario where freed memory is subsequently accessed, triggering undefined behavior and typically causing an application crash.

Attack Vector

The vulnerability is remotely exploitable over the network, though exploitation requires specific preconditions:

The target system must be running a vulnerable version of glibc
The /etc/nsswitch.conf file must have the hosts database configured with either SUCCESS=continue or SUCCESS=merge directives
An application must call the getaddrinfo function in a manner that triggers the vulnerable code path

An attacker could potentially craft network responses or manipulate DNS queries that cause the vulnerable code path to execute, resulting in denial of service. The attack complexity is high due to the specific configuration requirements needed for successful exploitation.

The vulnerability manifests during address resolution operations when non-standard nsswitch.conf configurations are present. Applications using getaddrinfo for hostname resolution may experience unexpected crashes when processing certain name resolution requests. For detailed technical analysis, see the Red Hat Bugzilla Report #2237798 and the OpenWall OSS Security Discussion.

Detection Methods for CVE-2023-4813

Indicators of Compromise

Unexpected application crashes in processes using getaddrinfo for name resolution
Core dumps showing crashes in gaih_inet or related glibc name resolution functions
Increased segmentation faults in network-facing applications
System logs indicating memory access violations during DNS resolution operations

Detection Strategies

Monitor for abnormal application terminations involving glibc name resolution components
Audit /etc/nsswitch.conf for SUCCESS=continue or SUCCESS=merge configurations in the hosts database entry
Implement application monitoring to detect crashes in getaddrinfo call paths
Review system logs for segmentation faults and memory access errors related to network operations

Monitoring Recommendations

Enable core dump collection and analysis for applications performing network name resolution
Configure centralized logging to capture application crashes across affected systems
Implement health checks for services that rely heavily on DNS resolution functionality
Monitor glibc-related security advisories from distribution vendors

How to Mitigate CVE-2023-4813

Immediate Actions Required

Verify glibc version installed on all Linux systems and identify vulnerable deployments
Review /etc/nsswitch.conf configuration files for SUCCESS=continue or SUCCESS=merge directives
Prioritize patching systems with the identified non-default nsswitch.conf configurations
Apply available security updates from your Linux distribution vendor

Patch Information

Security patches are available from multiple vendors:

Update glibc to the patched version available from your distribution's package repository.

Workarounds

Remove or modify SUCCESS=continue and SUCCESS=merge directives from the hosts database entry in /etc/nsswitch.conf if not required
Implement process restart mechanisms for critical applications to maintain availability
Consider isolating vulnerable systems until patches can be applied
Deploy network-level monitoring to detect potential exploitation attempts

bash

# Check nsswitch.conf for vulnerable configuration
grep -E "hosts:.*SUCCESS=(continue|merge)" /etc/nsswitch.conf

# Verify installed glibc version (RHEL/CentOS)
rpm -q glibc

# Verify installed glibc version (Debian/Ubuntu)
dpkg -l libc6

# Apply updates (RHEL/CentOS)
sudo yum update glibc

# Apply updates (Debian/Ubuntu)
sudo apt update && sudo apt upgrade libc6