CVE-2016-2225 in uClibc-ng
Summary
by MITRE
The __read_etc_hosts_r 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 a crafted packet.
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Analysis
by VulDB Data Team • 11/15/2022
The vulnerability identified as CVE-2016-2225 affects uClibc-ng versions prior to 1.0.12 and resides within the __read_etc_hosts_r function located in libc/inet/resolv.c. This flaw represents a critical security issue that can be exploited by remote attackers to induce a denial of service condition through manipulation of DNS responses. The vulnerability specifically targets the resolver functionality that handles host name resolution in embedded systems utilizing uClibc-ng as their standard C library implementation.
The technical mechanism behind this vulnerability involves a flaw in how the __read_etc_hosts_r function processes DNS packets received from remote servers. When a malicious DNS server crafts a specially formatted packet, the function enters an infinite loop during packet parsing and processing, effectively consuming system resources and rendering the affected system unavailable to legitimate users. This behavior constitutes a classic denial of service attack vector where the attacker does not need to compromise system credentials but can simply send malformed DNS responses to trigger the problematic code path. The infinite loop occurs because the function fails to properly validate or handle certain edge cases in DNS packet structures, particularly when processing response records that contain unexpected or malformed data.
The operational impact of this vulnerability extends beyond simple service disruption, as it can affect any embedded device or system that relies on uClibc-ng for name resolution services. This includes IoT devices, network appliances, routers, and other embedded systems where the affected library is commonly deployed. The vulnerability is particularly dangerous in environments where these systems are critical infrastructure components, as the denial of service can lead to complete system unavailability and potential business disruption. Network administrators and security teams face the challenge of identifying vulnerable systems across their networks, as the vulnerability may not be immediately apparent during normal operation but can be triggered by any DNS response that matches the crafted packet pattern.
Systems can be mitigated against this vulnerability through several approaches that align with established security practices and standards. The primary and most effective mitigation involves upgrading to uClibc-ng version 1.0.12 or later, which contains the patched implementation of the __read_etc_hosts_r function. Organizations should also consider implementing DNS filtering mechanisms and network segmentation to limit exposure to potentially malicious DNS servers. Additionally, monitoring network traffic for unusual DNS response patterns and implementing intrusion detection systems can help identify exploitation attempts. From a compliance perspective, this vulnerability aligns with CWE-835 which addresses infinite loops and the potential for denial of service through malformed input processing. The ATT&CK framework categorizes this vulnerability under the T1499.004 technique for network denial of service, specifically targeting the use of malformed network responses to cause system instability. Organizations should also consider implementing defensive measures such as DNS response validation, rate limiting for DNS queries, and regular security assessments to ensure all embedded systems maintain current security patches and configurations.