CVE-2013-7423 in C Library
Summary
by MITRE
The send_dg function in resolv/res_send.c in GNU C Library (aka glibc or libc6) before 2.20 does not properly reuse file descriptors, which allows remote attackers to send DNS queries to unintended locations via a large number of requests that trigger a call to the getaddrinfo function.
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Analysis
by VulDB Data Team • 03/08/2022
The vulnerability identified as CVE-2013-7423 represents a critical flaw in the GNU C Library's DNS resolution mechanism that has significant implications for network security and system integrity. This issue affects glibc versions prior to 2.20 and stems from improper file descriptor reuse within the send_dg function located in resolv/res_send.c. The flaw specifically manifests when the getaddrinfo function is repeatedly invoked, creating a scenario where DNS queries can be inadvertently redirected to unintended locations rather than the originally specified targets.
The technical root cause of this vulnerability lies in the improper management of file descriptors during DNS query processing. When multiple DNS requests are processed in rapid succession, the send_dg function fails to correctly close or reset file descriptors that are meant to be reused for subsequent queries. This mismanagement creates a condition where the underlying network socket state becomes corrupted or inconsistent, allowing attackers to manipulate the DNS resolution process through carefully crafted sequences of requests. The vulnerability operates at the system call level, specifically within the resolver library that handles DNS name resolution for applications.
From an operational standpoint, this vulnerability enables remote attackers to perform DNS spoofing or cache poisoning attacks with relatively low complexity. Attackers can exploit the flaw by sending a large volume of DNS queries that trigger the getaddrinfo function repeatedly, causing the system to redirect queries to malicious servers or alternative destinations. This capability undermines the fundamental trust model of DNS resolution and can lead to various security consequences including man-in-the-middle attacks, service disruption, or unauthorized access to systems. The impact extends beyond simple query redirection as it can compromise the integrity of the entire DNS resolution infrastructure on affected systems.
The vulnerability aligns with CWE-120, which addresses buffer overflow vulnerabilities, and maps to ATT&CK technique T1071.004 for application layer protocol: DNS, as it exploits weaknesses in DNS resolution mechanisms. Organizations affected by this vulnerability face significant risk of DNS-based attacks that can compromise network security and data integrity. The exploitability of this issue is particularly concerning because it requires minimal privileges and can be executed remotely without authentication. System administrators should prioritize patching affected glibc versions and implementing network monitoring to detect anomalous DNS query patterns that may indicate exploitation attempts.
Mitigation strategies include immediate deployment of glibc version 2.20 or later, which contains the necessary fixes to properly manage file descriptors during DNS resolution. Additional protective measures include implementing DNS query rate limiting, monitoring DNS traffic for suspicious patterns, and configuring firewalls to restrict DNS query sources. Organizations should also consider implementing DNS security extensions and monitoring for unauthorized DNS server changes that could indicate successful exploitation of this vulnerability. The fix addresses the core issue by ensuring proper file descriptor lifecycle management and preventing the reuse of connections that could lead to query redirection attacks.