CVE-2016-2224 in uClibc-ng
Summary
by MITRE
The __decode_dotted function in libc/inet/resolv.c in uClibc-ng before 1.0.12 allows remote DNS servers to cause a denial of service (infinite loop) via vectors involving compressed items in a reply.
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Analysis
by VulDB Data Team • 11/15/2022
The vulnerability identified as CVE-2016-2224 represents a critical denial of service flaw within the uClibc-ng C library implementation, specifically affecting versions prior to 1.0.12. This issue manifests in the __decode_dotted function located within the libc/inet/resolv.c file, which handles DNS resolution operations for embedded systems and devices utilizing this lightweight C library. The vulnerability stems from improper handling of compressed DNS resource records during the parsing of DNS responses from remote servers, creating a condition where maliciously crafted DNS replies can trigger infinite loop scenarios within the resolver logic.
The technical exploitation of this vulnerability occurs when a remote DNS server crafts a response containing compressed domain names that create circular references within the decompression process. The __decode_dotted function fails to properly validate the compression pointers and their referenced data, allowing attackers to construct DNS replies where compressed labels point back to previously encountered labels, creating an infinite loop during the decompression phase. This flaw falls under CWE-835, which specifically addresses the issue of loops with insufficient loop counters or loop termination conditions, and directly relates to the broader category of improper input validation in network protocols. The infinite loop occurs because the decompression algorithm does not maintain proper tracking of already visited compression pointers, leading to repeated processing of the same data structures.
From an operational perspective, this vulnerability poses significant risks to embedded devices, IoT systems, and network infrastructure that rely on uClibc-ng for DNS resolution services. Attackers can exploit this weakness by sending malicious DNS responses to vulnerable systems, causing them to enter infinite loops and consume excessive CPU resources until the system becomes unresponsive or crashes. This denial of service condition affects the availability of network services and can be particularly devastating in environments where continuous uptime is critical, such as industrial control systems, network appliances, and embedded network devices. The impact extends beyond simple service disruption to potentially compromising the overall network infrastructure, as affected devices may become unreachable or unable to process legitimate DNS requests.
Mitigation strategies for CVE-2016-2224 involve immediate patching of uClibc-ng installations to version 1.0.12 or later, which includes corrected validation logic for DNS compression pointer handling. System administrators should also implement DNS filtering mechanisms that can detect and block malformed DNS responses containing suspicious compression patterns. Network monitoring solutions should be enhanced to identify unusual CPU utilization patterns that may indicate exploitation attempts. Additionally, implementing DNSSEC validation and employing rate limiting on DNS query processing can provide additional defense layers. Organizations using embedded systems should conduct comprehensive vulnerability assessments to identify all devices utilizing affected uClibc-ng versions and prioritize remediation efforts based on the criticality of affected services. The vulnerability demonstrates the importance of proper input validation in network protocol implementations and aligns with ATT&CK technique T1499.004, which covers network denial of service attacks through malformed network traffic processing.