CVE-2023-4527 in C Library
Summary
by MITRE • 09/18/2023
A flaw was found in glibc. When the getaddrinfo function is called with the AF_UNSPEC address family and the system is configured with no-aaaa mode via /etc/resolv.conf, a DNS response via TCP larger than 2048 bytes can potentially disclose stack contents through the function returned address data, and may cause a crash.
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Analysis
by VulDB Data Team • 05/17/2025
The vulnerability identified as CVE-2023-4527 represents a critical security flaw within the GNU C Library (glibc) that affects how the getaddrinfo function processes DNS responses under specific network configurations. This issue manifests when systems are configured with no-aaaa mode through /etc/resolv.conf settings, creating a scenario where TCP-based DNS responses exceeding 2048 bytes can potentially expose sensitive stack memory contents. The flaw resides in the improper handling of DNS response data structures during address resolution operations, particularly when transitioning between IPv4 and IPv6 address families. The vulnerability is categorized under CWE-200, which deals with improper handling of sensitive information, and specifically relates to information exposure through memory disclosure mechanisms. The attack vector becomes particularly relevant in environments where DNS servers return large responses or when network configurations enforce specific address family handling behaviors.
The technical implementation of this vulnerability stems from how glibc manages memory allocation and data copying during DNS resolution processes. When getaddrinfo is invoked with AF_UNSPEC, the function attempts to resolve hostnames using both IPv4 and IPv6 protocols, but in no-aaaa mode configurations, IPv6 resolution is disabled. The flaw occurs when processing TCP-based DNS responses larger than the standard 2048 byte limit, where the function fails to properly validate or handle the buffer boundaries of the returned address data. This improper memory management creates opportunities for stack content leakage, potentially exposing sensitive information such as return addresses, local variables, or other memory contents that could aid in further exploitation attempts. The vulnerability directly impacts the memory safety mechanisms within glibc's DNS resolution stack and represents a classic buffer overread condition that could be exploited for information disclosure attacks.
The operational impact of CVE-2023-4527 extends beyond simple information disclosure, as it can potentially lead to system instability and crash conditions within affected applications. When DNS responses exceed 2048 bytes, the system may experience segmentation faults or memory corruption issues that could cause applications to terminate unexpectedly. This vulnerability affects any system running glibc versions where the getaddrinfo function is utilized for hostname resolution, particularly impacting web servers, email systems, and other network services that depend on proper DNS resolution. The vulnerability is especially concerning in environments where applications are not properly hardened against memory corruption issues, as it could provide attackers with valuable information for crafting more sophisticated attacks. From an attack framework perspective, this vulnerability aligns with techniques described in the MITRE ATT&CK framework under T1059 for command and control communications and T1068 for exploit development, as it provides potential pathways for information gathering and system compromise.
Mitigation strategies for CVE-2023-4527 primarily focus on updating glibc to patched versions that properly handle oversized DNS responses and implement appropriate buffer validation mechanisms. System administrators should immediately apply security patches from their respective distribution vendors, as the vulnerability affects core system libraries used by numerous applications. Additional defensive measures include monitoring DNS traffic for unusually large responses and implementing network-level controls to limit DNS response sizes when possible. Organizations should also review their /etc/resolv.conf configurations to ensure no-aaaa mode settings are properly implemented and consider implementing application-level protections against malformed DNS responses. The vulnerability highlights the importance of proper memory management in system libraries and demonstrates how seemingly minor implementation flaws can have significant security implications. Security teams should monitor for potential exploitation attempts and consider implementing intrusion detection rules that can identify abnormal DNS response patterns that might indicate exploitation attempts targeting this vulnerability.