CVE-2023-4806: GNU Glibc Use-After-Free Vulnerability

CVE-2023-4806 Overview

A Use-After-Free vulnerability has been identified in the GNU C Library (glibc), specifically within the getaddrinfo function. In an extremely rare situation, the getaddrinfo function may access memory that has been freed, resulting in an application crash and potential denial of service. This memory safety flaw occurs under very specific conditions involving NSS (Name Service Switch) module configurations.

Critical Impact

Applications relying on glibc's getaddrinfo function for hostname resolution may crash unexpectedly when specific NSS module configurations and query parameters align, potentially causing service disruptions across Linux-based infrastructure.

Affected Products

• GNU glibc 2.33
• Red Hat Enterprise Linux 7.0, 8.0, 9.0 (and EUS variants)
• Red Hat CodeReady Linux Builder (multiple architectures)
• Fedora 37, 38, 39

Discovery Timeline

• 2023-09-18 - CVE-2023-4806 published to NVD
• 2025-09-26 - Last updated in NVD database

Technical Details for CVE-2023-4806

Vulnerability Analysis

This vulnerability is a Use-After-Free (CWE-416) memory corruption issue in the glibc library's DNS resolution functionality. The flaw resides in the getaddrinfo function, which is a core system call used by virtually all networked applications on Linux systems to resolve hostnames to IP addresses.

The vulnerability is exploitable only under a highly specific set of conditions. First, a custom NSS module must be in use that implements only the _nss_*_gethostbyname2_r and _nss_*_getcanonname_r hooks without implementing the _nss_*_gethostbyname3_r hook. Second, the DNS query must return a large number of both IPv6 and IPv4 addresses for the resolved name. Third, the application must call getaddrinfo with the AF_INET6 address family specified along with the AI_CANONNAME, AI_ALL, and AI_V4MAPPED flags set simultaneously.

When these conditions are met, a race condition or memory management error causes the function to access previously freed memory, leading to undefined behavior—most commonly resulting in an application crash.

Root Cause

The root cause stems from improper memory lifecycle management within the getaddrinfo implementation when handling dual-stack (IPv4/IPv6) address resolution with canonical name lookup. When the NSS module lacks the _nss_*_gethostbyname3_r hook, the code path that handles address family mapping and canonical name resolution does not properly maintain references to allocated memory buffers. This results in a dangling pointer that may be dereferenced after the memory has been freed, triggering the Use-After-Free condition.

Attack Vector

The attack vector for this vulnerability is network-based but requires significant preconditions to be met. An attacker would need to either control or influence the DNS responses returned to a vulnerable application, ensuring that a large number of IPv4 and IPv6 addresses are returned. Additionally, the target system must have a specific NSS module configuration that omits the _nss_*_gethostbyname3_r hook implementation. The application must also make getaddrinfo calls with the precise combination of flags (AF_INET6, AI_CANONNAME, AI_ALL, AI_V4MAPPED).

Due to these stringent requirements, exploitation in real-world scenarios is considered extremely rare. However, in environments where these conditions exist, an attacker could potentially cause denial of service by triggering application crashes repeatedly.

Detection Methods for CVE-2023-4806

Indicators of Compromise

• Unexpected application crashes with segmentation faults during DNS resolution operations
• Core dumps showing stack traces involving getaddrinfo or related NSS functions
• Increased frequency of service restarts for applications performing hostname lookups

Detection Strategies

• Monitor system logs for SIGSEGV signals originating from processes performing network operations
• Implement application-level crash monitoring for services that heavily utilize DNS resolution
• Review NSS configuration files (/etc/nsswitch.conf) to identify custom module usage patterns
• Use memory sanitizers (AddressSanitizer) during development and testing to detect Use-After-Free conditions

Monitoring Recommendations

• Enable core dump collection and analysis for critical services using glibc DNS resolution
• Deploy SentinelOne Singularity Platform to monitor for anomalous application termination patterns
• Implement centralized logging to correlate crash events across multiple systems
• Configure alerting for services that restart frequently without apparent cause

How to Mitigate CVE-2023-4806

Immediate Actions Required

• Update glibc to the latest patched version available for your distribution
• Review and audit custom NSS modules to ensure complete hook implementation
• Consider implementing the _nss_*_gethostbyname3_r hook in any custom NSS modules
• Apply vendor-specific patches from Red Hat, Fedora, or Gentoo as applicable

Patch Information

Multiple vendors have released patches addressing this vulnerability:

• Red Hat: Red Hat Security Advisory RHSA-2023:5453, RHSA-2023:5455, and RHSA-2023:7409 provide patches for affected RHEL versions
• Fedora: Package updates available through the standard update channels for Fedora 37, 38, and 39
• Gentoo: GLSA 202310-03 addresses this vulnerability
• NetApp: NetApp Security Advisory NTAP-20240125-0008 provides guidance for affected NetApp products

For detailed technical information, refer to Red Hat Bugzilla Report #2237782.

Workarounds

• Avoid using custom NSS modules that do not implement the _nss_*_gethostbyname3_r hook
• Modify application code to avoid using the specific flag combination (AI_CANONNAME, AI_ALL, AI_V4MAPPED with AF_INET6) when possible
• Implement application-level retry logic to handle potential crashes gracefully
• Consider using alternative DNS resolution mechanisms for critical applications until patches can be applied

# Check current glibc version
ldd --version

# For RHEL/CentOS systems, update glibc
sudo yum update glibc

# For Fedora systems
sudo dnf update glibc

# Verify NSS module configuration
cat /etc/nsswitch.conf | grep hosts