CVE-2016-9778 in BIND
Summary
by MITRE
An error in handling certain queries can cause an assertion failure when a server is using the nxdomain-redirect feature to cover a zone for which it is also providing authoritative service. A vulnerable server could be intentionally stopped by an attacker if it was using a configuration that met the criteria for the vulnerability and if the attacker could cause it to accept a query that possessed the required attributes. Please note: This vulnerability affects the "nxdomain-redirect" feature, which is one of two methods of handling NXDOMAIN redirection, and is only available in certain versions of BIND. Redirection using zones of type "redirect" is not affected by this vulnerability. Affects BIND 9.9.8-S1 -> 9.9.8-S3, 9.9.9-S1 -> 9.9.9-S6, 9.11.0-9.11.0-P1.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 09/15/2024
The vulnerability described in CVE-2016-9778 represents a critical assertion failure in the Internet Systems Consortium BIND DNS server software that specifically impacts servers utilizing the nxdomain-redirect feature. This flaw exists within the DNS query processing logic when a server simultaneously provides authoritative service for a zone while also employing the nxdomain-redirect functionality to handle non-existent domain queries. The issue manifests when the server encounters certain malformed or specifically crafted queries that trigger an assertion failure, potentially leading to a complete service disruption. The vulnerability is particularly concerning because it can be exploited by remote attackers to intentionally crash the affected DNS server, effectively causing a denial of service condition that compromises the availability of critical DNS services. This vulnerability falls under the CWE-248 category of Uncaught Exception, specifically involving assertion failures that terminate program execution without proper error handling mechanisms. The attack vector requires that an attacker can influence the server to process a query with specific attributes that trigger the assertion failure condition, making it a targeted rather than broadly exploitable vulnerability.
The technical implementation of this vulnerability stems from the interaction between the nxdomain-redirect feature and the authoritative zone handling logic within BIND's DNS server implementation. When a server is configured to use nxdomain-redirect for a zone it also serves authoritatively, the internal state management becomes complex and prone to failure under specific query conditions. The assertion failure occurs during the processing of queries that should normally be handled gracefully but instead cause the server to terminate execution abruptly. This behavior is particularly dangerous in production environments where DNS servers are critical infrastructure components, as the crash can occur without proper logging or error recovery mechanisms. The vulnerability is specifically present in BIND versions 9.9.8-S1 through 9.9.8-S3, 9.9.9-S1 through 9.9.9-S6, and 9.11.0 through 9.11.0-P1, indicating that it was introduced in specific release branches and affects a narrow range of versions. The targeted nature of this vulnerability means that servers using the alternative redirection method based on zones of type "redirect" remain unaffected, providing a potential workaround for organizations that can modify their configuration.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromise the reliability and availability of DNS infrastructure that organizations depend upon for internet connectivity. When exploited successfully, the assertion failure can cause the BIND server process to terminate abruptly, requiring manual intervention to restart the service and potentially resulting in temporary loss of DNS resolution capabilities for affected domains. This type of vulnerability directly maps to ATT&CK technique T1499.004 which involves network denial of service attacks targeting DNS services. The vulnerability's impact is particularly severe in environments where DNS servers are critical for internal network operations, as it can lead to cascading failures affecting multiple services that depend on DNS resolution. Organizations using affected versions of BIND may experience unexpected downtime, service degradation, or even complete loss of DNS service availability, which can severely impact business operations and user access to network resources. The vulnerability also demonstrates poor defensive programming practices in the form of insufficient input validation and error handling in the DNS query processing pipeline.
Mitigation strategies for CVE-2016-9778 primarily involve upgrading to patched versions of BIND software, as the vulnerability was addressed in subsequent releases that corrected the assertion failure handling in the nxdomain-redirect feature. Organizations should prioritize updating their BIND installations to versions that have been verified to contain the appropriate fixes, ensuring that they move beyond the vulnerable version ranges specified in the CVE description. Additionally, administrators should consider disabling the nxdomain-redirect feature if it is not essential for their operational requirements, as this provides an immediate workaround that eliminates the attack surface. Network segmentation and monitoring solutions should be implemented to detect unusual query patterns that might indicate attempted exploitation of this vulnerability, as the attack requires specific query attributes to trigger the assertion failure. Implementing proper input validation and robust error handling mechanisms within DNS server configurations can also help mitigate the risk, though this requires careful configuration changes that must be thoroughly tested in production environments. Security teams should also consider implementing rate limiting and query filtering mechanisms to reduce the likelihood of successful exploitation attempts, while maintaining comprehensive logging to detect potential attack patterns. The vulnerability highlights the importance of thorough testing and validation of DNS server configurations, particularly when implementing advanced features like nxdomain-redirect that can introduce complex interaction points between different server functionalities.