CVE-2026-4891 in dnsmasq
Summary
by MITRE • 05/11/2026
A heap-based out-of-bounds read vulnerability in the DNSSEC validation of dnsmasq allows remote attackers to cause a denial of service via a crafted DNS packet.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 07/03/2026
The heap-based out-of-bounds read vulnerability in dnsmasq's DNSSEC validation component represents a critical security flaw that can be exploited by remote attackers to execute denial of service attacks. This vulnerability specifically affects the DNS resolver implementation within dnsmasq software, which is widely deployed in network infrastructure devices, home routers, and enterprise environments as a lightweight DNS caching server. The issue manifests when the software processes DNS packets containing malformed DNSSEC records, particularly in the validation logic that handles resource record signatures and key data structures. The out-of-bounds read occurs in heap memory management when the application attempts to access memory locations beyond the allocated buffer boundaries during DNSSEC validation operations, potentially leading to application crashes or unpredictable behavior.
The technical exploitation of this vulnerability stems from insufficient input validation within the DNSSEC processing pipeline of dnsmasq. When a maliciously crafted DNS packet containing oversized or malformed DNSSEC records is received, the validation routine fails to properly bounds-check memory accesses during signature verification or key processing operations. This flaw falls under the CWE-125 vulnerability category, which specifically addresses out-of-bounds read conditions in heap memory allocations. The vulnerability can be triggered through various DNSSEC-related record types including RRSIG, DNSKEY, and DS records, where the attacker can manipulate the length fields or record structures to cause the heap memory access violation. The memory corruption occurs in the heap-based data structures used to store DNSSEC validation state information, making the exploitation particularly dangerous as it can lead to complete service disruption.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as it can affect network availability and reliability across numerous devices and systems that rely on dnsmasq for DNS resolution services. Network administrators may experience intermittent service disruptions, complete DNS resolution failures, or cascading effects when multiple devices in a network segment are affected by the same vulnerable dnsmasq instance. The vulnerability affects a broad range of deployment scenarios including residential gateways, enterprise network appliances, and embedded systems running dnsmasq as their primary DNS resolver. In environments where DNSSEC validation is enabled, the attack surface expands significantly since the vulnerability is triggered specifically during DNSSEC processing, making it particularly dangerous for security-conscious deployments that rely on DNSSEC for integrity protection. The impact is amplified in scenarios where dnsmasq serves as a critical component in larger network architectures, potentially affecting downstream services and applications that depend on stable DNS resolution.
Organizations should implement immediate mitigations including updating to patched versions of dnsmasq where available, disabling DNSSEC validation temporarily if the feature is not required for security policies, and implementing network-level monitoring to detect and block suspicious DNS packet patterns. The vulnerability demonstrates the importance of proper memory management and bounds checking in network services, aligning with ATT&CK technique T1499.004 for network denial of service attacks. Security teams should also consider implementing intrusion detection systems that can identify malformed DNS packets targeting DNSSEC validation routines, as well as establishing network segmentation to limit the potential impact of successful exploitation. Regular vulnerability assessments and security audits of network infrastructure components should be conducted to identify similar memory safety issues in other network services and applications. The incident underscores the critical need for thorough input validation and memory safety practices in network-facing applications, particularly those handling complex protocol parsing scenarios like DNSSEC validation which involves intricate cryptographic data structures and state management operations.