CVE-2016-5417 in C Library
Summary
by MITRE
Memory leak in the __res_vinit function in the IPv6 name server management code in libresolv in GNU C Library (aka glibc or libc6) before 2.24 allows remote attackers to cause a denial of service (memory consumption) by leveraging partial initialization of internal resolver data structures.
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Analysis
by VulDB Data Team • 09/12/2022
The vulnerability identified as CVE-2016-5417 represents a critical memory management flaw within the GNU C Library's resolver functionality, specifically affecting the __res_vinit function in IPv6 name server handling code. This issue exists in glibc versions prior to 2.24 and demonstrates how improper resource cleanup during partial initialization can lead to significant system instability. The vulnerability operates at the core networking layer of Unix-like systems, where the resolver library manages DNS query processing and name server configuration. When the resolver encounters certain malformed or unexpected DNS responses during IPv6 name resolution, the __res_vinit function fails to properly clean up allocated memory resources, resulting in progressive memory consumption that can eventually exhaust available system resources.
The technical mechanism behind this vulnerability stems from the improper handling of internal resolver data structures during partial initialization scenarios. When the resolver attempts to process IPv6 name server information and encounters conditions that prevent complete initialization of its internal state, the memory allocated for these structures remains unreleased. This memory leak occurs because the function does not properly execute cleanup routines when initialization fails partway through the process, leading to a gradual accumulation of unreclaimed memory blocks. The flaw is particularly insidious because it operates silently in the background, consuming system resources incrementally until the system becomes unresponsive or crashes. The vulnerability specifically affects the resolver's ability to manage IPv6 name server entries, where partial initialization occurs when the resolver encounters malformed DNS responses or network conditions that prevent proper configuration of IPv6 name server addresses.
From an operational perspective, this vulnerability creates a significant denial of service risk for systems relying on glibc's resolver functionality. Remote attackers can exploit this weakness by sending specially crafted DNS responses or manipulating network conditions to trigger the partial initialization scenario repeatedly. The memory consumption pattern makes this vulnerability particularly dangerous in high-traffic environments where DNS queries are frequent, as the system's memory usage will gradually increase until it reaches critical levels. The impact extends beyond simple service disruption to potentially affecting system stability and performance across multiple applications that depend on the resolver library. This vulnerability is classified under CWE-401 as a weakness related to improper management of memory resources, specifically highlighting the failure to release memory after use during error conditions. The attack surface is broad as any application that utilizes standard DNS resolution functions within glibc is potentially affected, including web servers, database systems, and network management tools.
The mitigation strategy for CVE-2016-5417 requires immediate system updates to glibc version 2.24 or later, which contains the necessary patches to properly handle memory cleanup during partial initialization scenarios. System administrators should prioritize patching all affected systems, particularly those handling high volumes of DNS queries or serving critical network services. Additional protective measures include implementing DNS query rate limiting and monitoring for unusual memory consumption patterns in resolver processes. Network segmentation and firewall rules can help limit exposure by restricting access to systems running vulnerable versions of glibc. Organizations should also consider implementing intrusion detection systems that can identify abnormal DNS response patterns that may indicate exploitation attempts. The vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks through resource exhaustion, and demonstrates how memory management flaws can be leveraged to create persistent system instability. Regular security audits of system libraries and maintaining up-to-date software inventories are essential practices to prevent exploitation of similar vulnerabilities in the future.