CVE-2026-42387 in Recursor
Summary
by MITRE • 06/25/2026
A malicious authoritative server can send a crafted zone via the ZoneToCache function that leads to a crash of the Recursor due to insuffcient input validation.
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Analysis
by VulDB Data Team • 06/26/2026
This vulnerability represents a critical input validation flaw in DNS recursive resolvers that can be exploited through crafted zone data delivered by malicious authoritative servers. The issue specifically manifests within the ZoneToCache function where insufficient validation of incoming zone data allows attackers to construct specially formatted records that trigger a crash in the recursor daemon. This type of vulnerability falls under CWE-129 Input Validation and is classified as a buffer overflow or memory corruption issue that can lead to denial of service conditions. The technical flaw occurs when the recursive resolver processes zone transfer data without proper bounds checking or sanitization, enabling an attacker to craft malformed DNS records that cause the application to crash when attempting to cache the invalid zone information.
The operational impact of this vulnerability extends beyond simple service disruption as it can be leveraged for targeted denial of service attacks against DNS infrastructure. When exploited, the crash results in immediate service unavailability for the affected recursive resolver, potentially affecting thousands of downstream clients who rely on that specific DNS server for name resolution. Attackers can maintain persistent control over the attack vector by continuously sending crafted zone data through authoritative servers they control or have compromised, making this vulnerability particularly dangerous in environments where recursive resolvers process zone transfers from untrusted sources. The vulnerability can be exploited without requiring authentication or specialized privileges, making it an attractive target for adversaries seeking to disrupt DNS services at scale.
Mitigation strategies should focus on implementing comprehensive input validation mechanisms within the ZoneToCache function and establishing strict bounds checking for all incoming zone data. Organizations should deploy rate limiting controls on zone transfer requests and implement proper access controls to restrict which authoritative servers can initiate zone transfers to recursive resolvers. Network-level protections such as DNS firewall rules that filter suspicious zone data patterns and monitoring systems that detect unusual crash patterns or zone transfer activities should be implemented alongside application-level fixes. The vulnerability aligns with attack techniques documented in the MITRE ATT&CK framework under T1496 Resource Hijacking and T1566 Phishing, where adversaries leverage DNS infrastructure to establish persistent control over network resources. Regular patching of recursive resolver software and implementation of automated monitoring for crash events will significantly reduce the risk exposure while maintaining service availability for legitimate users who depend on proper DNS resolution capabilities.