CVE-2020-8619 in BIND
Summary
by MITRE
Unless a nameserver is providing authoritative service for one or more zones and at least one zone contains an empty non-terminal entry containing an asterisk ("*") character, this defect cannot be encountered. A would-be attacker who is allowed to change zone content could theoretically introduce such a record in order to exploit this condition to cause denial of service, though we consider the use of this vector unlikely because any such attack would require a significant privilege level and be easily traceable.
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Analysis
by VulDB Data Team • 10/25/2020
The vulnerability described in CVE-2020-8619 represents a specific denial of service condition within DNS server implementations that occurs under very particular circumstances. This defect is classified as a weakness in the authoritative DNS service handling logic where the system fails to properly process certain zone records that contain empty non-terminal entries with asterisk characters. The vulnerability demonstrates a classic example of how seemingly benign DNS record configurations can create exploitable conditions when combined with specific operational contexts. According to the Common Weakness Enumeration framework, this issue aligns with CWE-476 which describes NULL Pointer Dereference, though the manifestation here is more specific to DNS zone processing logic. The condition requires a precise set of prerequisites to be exploitable, making it a low-probability vulnerability that exists in the intersection of specific DNS server configurations and zone data structures.
The technical flaw manifests when a DNS server processes zone data containing empty non-terminal entries with asterisk wildcards, particularly within authoritative service contexts. This condition creates a scenario where the server's zone processing logic fails to properly handle the wildcard character within empty non-terminal entries, potentially leading to system resource exhaustion or service interruption. The asterisk character in DNS zone files typically serves as a wildcard for record matching, but when it appears in empty non-terminal positions, it creates an edge case in the parsing and processing algorithms. The vulnerability is particularly interesting from a security perspective because it demonstrates how DNS server implementations can fail to properly validate or sanitize zone data structures, creating potential denial of service vectors through legitimate configuration changes. This behavior falls under the ATT&CK technique T1499.004 for Network Denial of Service, as it can be leveraged to disrupt DNS service availability.
Operational impact assessment reveals that while this vulnerability is theoretically exploitable, practical attack scenarios are highly constrained due to the specific prerequisites required. The attack vector necessitates an attacker with significant privileges to modify zone content, making it difficult to execute without insider threat involvement or compromised administrative credentials. The requirement for a nameserver to provide authoritative service for zones containing empty non-terminal entries with asterisk characters creates a natural barrier to exploitation that significantly reduces the attack surface. However, the potential for disruption remains substantial since DNS services form the backbone of internet infrastructure, and any denial of service condition in authoritative DNS servers can cascade into broader service availability issues. The vulnerability's low exploitability factor does not diminish its importance, as it represents a potential point of failure in critical infrastructure components that could be leveraged by determined attackers with appropriate access levels.
Mitigation strategies for CVE-2020-8619 should focus on implementing robust input validation and sanitization within DNS server implementations. Administrators should ensure that zone data is properly validated before processing, particularly focusing on edge cases involving wildcard characters in non-terminal positions. The implementation of automated monitoring and alerting systems for unusual zone record patterns can help detect potential exploitation attempts. Regular security audits of DNS configurations should include checks for empty non-terminal entries with asterisk characters, as these represent a known problematic pattern. System administrators should also consider implementing least privilege access controls for zone modification operations to limit the potential for unauthorized changes that could trigger this vulnerability. Vendor-specific patches and updates should be applied promptly to address the underlying implementation flaw, and organizations should maintain comprehensive backup and recovery procedures for DNS zone data to ensure rapid restoration in case of service disruption. The vulnerability's characteristics make it particularly suitable for defense in depth approaches that combine configuration hardening with operational monitoring to provide comprehensive protection against potential exploitation.