CVE-2023-2829 in BIND
Summary
by MITRE • 06/21/2023
A `named` instance configured to run as a DNSSEC-validating recursive resolver with the Aggressive Use of DNSSEC-Validated Cache (RFC 8198) option (`synth-from-dnssec`) enabled can be remotely terminated using a zone with a malformed NSEC record. This issue affects BIND 9 versions 9.16.8-S1 through 9.16.41-S1 and 9.18.11-S1 through 9.18.15-S1.
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Analysis
by VulDB Data Team • 06/22/2023
The vulnerability described in CVE-2023-2829 represents a critical denial-of-service flaw within the Internet Systems Consortium BIND DNS server implementation. This issue specifically targets named instances configured to function as DNSSEC-validating recursive resolvers with the aggressive use of DNSSEC-validated cache feature enabled. The flaw manifests when the system encounters a malformed NSEC record within a DNS zone, leading to a remote termination of the named process. The vulnerability affects a substantial range of BIND 9 versions, spanning from 9.16.8-S1 through 9.16.41-S1 and 9.18.11-S1 through 9.18.15-S1, indicating a widespread impact across multiple stable release lines. The root cause stems from insufficient validation of NSEC record structures during the DNSSEC validation process, particularly when processing records that should be handled through the RFC 8198 mechanism. This represents a fundamental failure in input sanitization and error handling within the DNSSEC validation subsystem.
The technical exploitation of this vulnerability occurs through the manipulation of DNS zone data containing malformed NSEC records, which when processed by a vulnerable named instance, triggers an unhandled exception or memory corruption that results in process termination. The Aggressive Use of DNSSEC-Validated Cache option, also known as synth-from-dnssec, enables named to synthesize NSEC records from DNSSEC-validated data, creating an additional attack surface when malformed records are present. This flaw aligns with CWE-129, which covers improper validation of array indices, and CWE-248, dealing with uncaught exceptions in programs. The vulnerability operates at the application layer within the DNS protocol stack, specifically targeting the DNSSEC validation logic that processes zone data for recursive resolution. The attack requires only the ability to influence DNS responses or zone data that will be processed by the vulnerable named instance, making it particularly dangerous in environments where recursive resolvers are exposed to untrusted DNS data.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the availability of DNS resolution services within affected networks. When exploited, the remote termination of named processes can lead to cascading failures in DNS resolution, affecting numerous dependent services and applications that rely on proper DNS functionality. Organizations running vulnerable BIND instances as recursive resolvers face significant risk, particularly in environments where they handle DNS queries from external sources or when operating in configurations that enable aggressive DNSSEC validation. The vulnerability's remote exploitability means that attackers can trigger the flaw from outside the network perimeter, making it a particularly attractive target for denial-of-service attacks that can disrupt critical infrastructure services. This vulnerability directly impacts the availability and reliability of DNS services, which forms the foundation of internet infrastructure and can affect authentication, web browsing, email services, and countless other applications.
Mitigation strategies for this vulnerability should prioritize immediate patching of affected BIND versions to the latest stable releases that contain the necessary fixes for the NSEC record validation logic. Organizations should also consider implementing network segmentation and access controls to limit exposure of vulnerable recursive resolvers to untrusted DNS sources. The implementation of DNS security measures such as DNS Firewall rules, DNS query rate limiting, and monitoring for anomalous DNS responses can help detect and prevent exploitation attempts. Additionally, administrators should evaluate whether the aggressive use of DNSSEC-validated cache feature is essential for their deployment, as disabling this feature may prevent exploitation while maintaining basic DNS resolution functionality. The remediation process should include comprehensive testing of patched systems to ensure that the fix properly addresses the underlying validation issue without introducing regressions in DNSSEC validation capabilities. Security monitoring should be enhanced to detect potential exploitation attempts through unusual DNS query patterns or service disruptions that may indicate successful exploitation of this vulnerability.