CVE-2018-5736 in BIND
Summary
by MITRE
An error in zone database reference counting can lead to an assertion failure if a server which is running an affected version of BIND attempts several transfers of a slave zone in quick succession. This defect could be deliberately exercised by an attacker who is permitted to cause a vulnerable server to initiate zone transfers (for example: by sending valid NOTIFY messages), causing the named process to exit after failing the assertion test. Affects BIND 9.12.0 and 9.12.1.
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Analysis
by VulDB Data Team • 03/14/2023
The vulnerability described in CVE-2018-5736 represents a critical flaw in the Internet Systems Consortium BIND DNS server software that manifests through improper handling of zone database reference counting mechanisms. This issue specifically impacts BIND versions 9.12.0 and 9.12.1, where the software fails to correctly manage memory references during zone transfer operations, creating a potential denial of service condition that can be exploited by malicious actors. The flaw exists within the core DNS server functionality that governs how slave servers handle zone data synchronization from master servers, making it particularly dangerous in environments where DNS services are critical to network operations.
The technical implementation of this vulnerability stems from a race condition in the zone database reference counting logic that occurs during rapid successive zone transfers. When a vulnerable BIND server receives multiple NOTIFY messages in quick succession, each triggering a zone transfer operation, the reference counting mechanism fails to properly decrement or increment reference counters for zone data structures. This leads to an assertion failure within the named process, causing the server to terminate unexpectedly. The flaw operates at the level of the DNS server's internal memory management and resource handling, specifically affecting how slave zones are maintained and updated. According to CWE-611, this represents an improper access to resources through reference counting, while the behavior aligns with ATT&CK technique T1499.004 for network denial of service attacks.
The operational impact of CVE-2018-5736 extends beyond simple service disruption, as it can be actively exploited by attackers who gain the ability to trigger zone transfer operations on vulnerable servers. An attacker with the capability to send valid NOTIFY messages to a target BIND server can deliberately cause the assertion failure and subsequent process termination, effectively taking the DNS service offline. This creates a significant availability risk for organizations relying on DNS infrastructure, particularly in scenarios where multiple zone transfers occur simultaneously or where attackers can influence the timing of zone update notifications. The vulnerability's exploitation requires minimal privileges and can be executed remotely, making it a particularly attractive target for attackers seeking to disrupt network services. Organizations with multiple DNS servers in a master-slave configuration face heightened risk, as a single vulnerable slave server can become a point of failure that affects the entire DNS resolution infrastructure.
Mitigation strategies for this vulnerability require immediate patching of affected BIND installations to versions that contain the corrected reference counting implementation. Organizations should prioritize updating their DNS infrastructure to BIND 9.12.2 or later, which includes the necessary fixes for the zone database reference counting issue. Additionally, network administrators should implement monitoring for unusual patterns of NOTIFY messages or zone transfer activity that could indicate attempted exploitation. The vulnerability highlights the importance of proper resource management in server applications and demonstrates how seemingly minor memory handling flaws can result in significant service disruption. Security teams should also consider implementing access controls to limit who can send NOTIFY messages to DNS servers, reducing the attack surface for this particular vulnerability while maintaining operational requirements for legitimate zone synchronization.