CVE-2021-45951 in Dnsmasq
Summary
by MITRE • 01/01/2022
Dnsmasq 2.86 has a heap-based buffer overflow in check_bad_address (called from check_for_bogus_wildcard and FuzzCheckForBogusWildcard).
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Analysis
by VulDB Data Team • 08/04/2024
The heap-based buffer overflow vulnerability identified as CVE-2021-45951 affects Dnsmasq version 2.86 and represents a critical security flaw that can lead to arbitrary code execution. This vulnerability resides within the check_bad_address function which is invoked from two primary code paths including check_for_bogus_wildcard and FuzzCheckForBogusWildcard. The flaw manifests when processing DNS responses containing malformed wildcard records that trigger improper memory handling during address validation operations. The vulnerability falls under CWE-121 heap-based buffer overflow classification, which specifically addresses situations where insufficient bounds checking allows attackers to write beyond allocated memory boundaries. This particular implementation flaw demonstrates a classic memory corruption vulnerability that can be exploited through carefully crafted DNS responses.
The operational impact of this vulnerability extends beyond simple denial of service scenarios to encompass full system compromise capabilities. When exploited, the buffer overflow can overwrite adjacent heap memory locations potentially leading to stack corruption, function pointer overwrites, or return address manipulation. Attackers can leverage this vulnerability by crafting malicious DNS responses that contain oversized or malformed wildcard records, which when processed by the vulnerable Dnsmasq instance trigger the exploitable code path. The vulnerability affects systems running Dnsmasq 2.86 and potentially earlier versions that contain the same flawed code patterns, making it particularly dangerous in environments where DNS services are exposed to untrusted network traffic.
Security implications of CVE-2021-45951 align with ATT&CK technique T1203, specifically targeting the exploitation of memory corruption vulnerabilities to gain unauthorized access. The vulnerability can be exploited through DNS-based attack vectors, making it particularly relevant in environments where DNS servers act as central points of failure. Network administrators should consider this vulnerability as part of broader DNS security assessments and implement appropriate monitoring for anomalous DNS traffic patterns. The flaw demonstrates poor input validation practices and inadequate memory management within the DNS resolution process, creating opportunities for privilege escalation attacks when Dnsmasq operates with elevated privileges. Organizations relying on Dnsmasq for DNS services, DHCP, or DNS forwarding must urgently evaluate their exposure and implement immediate mitigations.
Mitigation strategies for CVE-2021-45951 should include immediate deployment of patched Dnsmasq versions that address the heap overflow conditions. System administrators should also implement network-level controls such as DNS response rate limiting, DNS query filtering, and monitoring for unusual wildcard record patterns. The implementation of DNS security extensions including DNSSEC validation can provide additional layers of protection against malformed DNS responses. Network segmentation and access controls should be strengthened to limit exposure of vulnerable Dnsmasq instances to untrusted networks. Regular security assessments and penetration testing should include verification of DNS service configurations to ensure proper input validation and memory handling practices. Organizations should also establish incident response procedures specifically addressing DNS-based memory corruption vulnerabilities and maintain up-to-date threat intelligence regarding similar exploitation patterns in DNS services.