CVE-2020-8622 in Communications Diameter Signaling Router
Summary
by MITRE
In BIND 9.0.0 -> 9.11.21, 9.12.0 -> 9.16.5, 9.17.0 -> 9.17.3, also affects 9.9.3-S1 -> 9.11.21-S1 of the BIND 9 Supported Preview Edition, An attacker on the network path for a TSIG-signed request, or operating the server receiving the TSIG-signed request, could send a truncated response to that request, triggering an assertion failure, causing the server to exit. Alternately, an off-path attacker would have to correctly guess when a TSIG-signed request was sent, along with other characteristics of the packet and message, and spoof a truncated response to trigger an assertion failure, causing the server to exit.
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Analysis
by VulDB Data Team • 05/21/2025
The vulnerability identified as CVE-2020-8622 represents a critical assertion failure in the Berkeley Internet Name Domain (BIND) software that affects multiple versions across different release branches. This security flaw specifically targets TSIG (Transaction Signatures) signed requests within the DNS infrastructure, creating a potential denial of service condition that could bring down DNS servers. The vulnerability exists in BIND versions from 9.0.0 through 9.11.21, 9.12.0 through 9.16.5, and 9.17.0 through 9.17.3, including the supported preview edition versions. The flaw stems from improper handling of truncated responses during TSIG-signed request processing, where the server fails to properly validate response integrity and terminates execution upon encountering malformed truncated responses.
The technical implementation of this vulnerability exploits the way BIND processes TSIG-signed DNS requests and responses. When a TSIG-signed request is processed, the server expects a complete and valid response to validate the transaction signature. However, the flaw allows an attacker to send a truncated response that triggers an assertion failure within the BIND server code. This assertion failure occurs because the server does not properly validate the response length or structure before attempting to process the TSIG validation logic. The assertion failure causes the server to terminate abruptly, leading to a denial of service condition that prevents legitimate DNS queries from being processed. This vulnerability operates through the network layer where DNS traffic flows, making it particularly dangerous in environments where DNS servers handle critical infrastructure traffic.
The operational impact of CVE-2020-8622 extends beyond simple service disruption to potentially compromise entire DNS infrastructures. The vulnerability affects both on-path and off-path attackers, though the attack vectors differ in complexity and feasibility. An on-path attacker with access to the network path can directly intercept TSIG-signed requests and inject truncated responses to trigger the assertion failure. This scenario is particularly concerning in environments where DNS servers communicate over unencrypted channels or where attackers have visibility into the network traffic. Off-path attackers face greater challenges as they must accurately guess timing characteristics, packet characteristics, and message properties to successfully spoof a truncated response that triggers the assertion failure. The vulnerability aligns with CWE-248, which describes an unspecified flaw in the program, and represents a direct violation of the principle of robust error handling in network services.
Mitigation strategies for CVE-2020-8622 focus on both immediate patching and operational security measures. The primary solution involves upgrading to patched versions of BIND where the assertion failure has been resolved through proper validation of response structures and implementation of robust error handling mechanisms. Organizations should prioritize upgrading their DNS infrastructure to versions that have addressed this vulnerability, particularly those in the 9.11.22, 9.16.6, and 9.17.4 release branches. Network segmentation and access controls can provide additional defense-in-depth measures by limiting which systems can initiate TSIG-signed requests and by implementing monitoring for unusual DNS response patterns. The vulnerability demonstrates the importance of implementing proper input validation and error handling in network services, aligning with ATT&CK technique T1499.004 which covers network denial of service attacks. Organizations should also consider implementing intrusion detection systems that can identify suspicious truncated DNS response patterns and establish monitoring for unexpected server terminations.
The vulnerability serves as a reminder of the critical importance of proper error handling in DNS infrastructure software. The flaw demonstrates how seemingly minor validation gaps in network protocol implementations can lead to catastrophic service disruptions. Organizations relying on DNS for critical infrastructure services must maintain robust patch management processes and ensure that DNS server software remains up-to-date with security patches. The security implications extend beyond immediate service disruption to include potential compromise of DNS cache poisoning scenarios and broader infrastructure availability concerns. This vulnerability reinforces the need for comprehensive security testing of network protocol implementations and proper validation of all network response handling mechanisms to prevent assertion failures that could be exploited for denial of service attacks.