CVE-2023-4527: GNU Glibc Information Disclosure Flaw

CVE-2023-4527 Overview

A stack buffer over-read vulnerability was discovered in the GNU C Library (glibc) affecting the getaddrinfo function. When getaddrinfo is called with the AF_UNSPEC address family on systems configured with no-aaaa mode via /etc/resolv.conf, a DNS response received via TCP that exceeds 2048 bytes can trigger an out-of-bounds read. This vulnerability can potentially disclose stack contents through the function's returned address data and may cause application crashes, leading to denial of service conditions.

Critical Impact

This vulnerability can lead to information disclosure of sensitive stack memory contents and denial of service through application crashes on Linux systems using affected glibc versions.

Affected Products

• GNU glibc (multiple versions)
• Red Hat Enterprise Linux 8.x and 9.x
• Fedora 37, 38, and 39
• Red Hat CodeReady Linux Builder (various architectures)
• NetApp H300s, H500s, H700s, H410s, and H410c firmware

Discovery Timeline

• September 18, 2023 - CVE-2023-4527 published to NVD
• June 24, 2025 - Last updated in NVD database

Technical Details for CVE-2023-4527

Vulnerability Analysis

The vulnerability exists in glibc's DNS resolution functionality, specifically within the getaddrinfo function. The flaw occurs due to improper handling of DNS responses when the system is configured to disable AAAA (IPv6) record queries through the no-aaaa option in /etc/resolv.conf. Under these specific conditions, when a DNS response is transmitted over TCP and exceeds 2048 bytes in size, the function fails to properly validate buffer boundaries, resulting in a stack buffer over-read condition.

This memory safety issue falls under CWE-121 (Stack-based Buffer Overflow) and CWE-125 (Out-of-bounds Read). The vulnerability requires network access to exploit, as an attacker must be positioned to send malicious DNS responses to the target system. While the attack complexity is high due to the specific configuration requirements (no-aaaa mode must be enabled), successful exploitation does not require authentication or user interaction.

Root Cause

The root cause stems from insufficient bounds checking in the DNS response parsing logic within glibc's resolver implementation. When processing TCP-based DNS responses larger than 2048 bytes while operating in no-aaaa mode, the code reads beyond the allocated stack buffer. This occurs because the response handling code does not properly account for the buffer size limitations when the no-aaaa configuration option modifies the expected response handling behavior.

Attack Vector

The attack is network-based and requires the attacker to control or manipulate DNS responses reaching the target system. The attack scenario involves:

1. The target system must have /etc/resolv.conf configured with the no-aaaa option
2. An application on the target system calls getaddrinfo with AF_UNSPEC address family
3. The attacker sends a crafted DNS response via TCP that exceeds 2048 bytes
4. The oversized response triggers the out-of-bounds read, potentially leaking stack contents or causing a crash

This could be achieved through DNS cache poisoning, man-in-the-middle attacks on DNS traffic, or by compromising a DNS server that the target system queries.

Detection Methods for CVE-2023-4527

Indicators of Compromise

• Unusual application crashes in services that perform DNS resolution via getaddrinfo
• Abnormally large DNS responses (exceeding 2048 bytes) received over TCP connections
• Unexpected memory access errors or segmentation faults in glibc-linked applications
• DNS query patterns indicating potential exploitation attempts targeting resolver functions

Detection Strategies

• Monitor for DNS TCP responses exceeding 2048 bytes, particularly when systems are configured with no-aaaa mode
• Implement network-level detection rules to identify oversized DNS response packets transmitted via TCP
• Deploy host-based monitoring to detect abnormal crashes in applications utilizing glibc DNS resolution
• Use SentinelOne's behavioral AI engine to detect memory corruption exploitation patterns in real-time

Monitoring Recommendations

• Enable DNS query and response logging to identify anomalous traffic patterns
• Configure crash reporting and analysis tools to capture and analyze segmentation faults in glibc-dependent applications
• Monitor system logs for resolver-related errors that may indicate exploitation attempts
• Implement network segmentation to limit exposure of systems using vulnerable glibc versions to untrusted DNS servers

How to Mitigate CVE-2023-4527

Immediate Actions Required

• Update glibc to the latest patched version available for your distribution
• Review /etc/resolv.conf configuration and assess the necessity of the no-aaaa option
• If the no-aaaa option is not required, consider removing it as a temporary workaround
• Prioritize patching on internet-facing systems and those processing DNS queries from untrusted sources

Patch Information

Security patches are available from multiple vendors. Red Hat has released advisories RHSA-2023:5453 and RHSA-2023:5455 addressing this vulnerability. Fedora users should apply updates via the standard package management system as announced in the Fedora package announcements. Gentoo users should reference GLSA 202310-03 for remediation guidance. NetApp has also released advisory ntap-20231116-0012 for affected storage systems.

Workarounds

• Remove or comment out the no-aaaa option from /etc/resolv.conf if IPv6 DNS queries are acceptable in your environment
• Implement DNS response size filtering at the network level to block TCP responses exceeding normal thresholds
• Use local DNS caching servers with response validation to filter potentially malicious oversized responses
• Consider implementing DNSSEC validation to reduce the risk of DNS response manipulation

# Check if no-aaaa is configured in resolv.conf
grep -i "no-aaaa" /etc/resolv.conf

# Verify installed glibc version
ldd --version

# Example: Remove no-aaaa option (backup first)
sudo cp /etc/resolv.conf /etc/resolv.conf.backup
sudo sed -i '/no-aaaa/d' /etc/resolv.conf