DNS Server Vulnerability: Single DNS Packet can Bring Down the System

A new flaw has been discovered in DNSSEC, which, when exploited by threat actors, could result in the unavailability of technologies such as web browsing, email, and instant messaging. This new class of attacks has been termed “KeyTrap” by researchers. 

Moreover, a threat actor could completely disable large parts of the worldwide internet. KeyTrap attacks affect not only DNS but also the applications using it. The “KeyTrap” class of attacks has been assigned with CVE-2023-50387, and the severity is yet to be categorized.  As of December 2023, 31.47% of the web clients used DNSSEC-validating DNS resolvers worldwide. 

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Technical Analysis

CVE-2023-50387: DNSSEC validator

This particular vulnerability exists due to the processing of responses from specially crafted DNSSEC-signed zones, which causes CPU exhaustion on a DNSSEC-validating resolver.

Successful exploitation of this vulnerability could significantly affect the resolver’s performance, disrupting the DNS resolution service.

As a workaround, DNSSEC validation can be disabled entirely, preventing this vulnerability. However, this was not a recommended resolution. Additionally, there is no evidence of active exploitation of this vulnerability by threat actors.

To fix this vulnerability, it is advised to upgrade to the following versions of BIND 9 and BIND Supported Preview Edition:

Nevertheless, researchers also stated that “The flaws are not recent,” describing an obsolete internet standard, RFC 2535, from 1999. Fast forwarding to 2012, there was another implementation flaw for DNSSEC validation in standards RFC 6781 and RFC 6840. 

Although this vulnerability has existed for the past 25 years, it went unnoticed by the community due to the complexity of the DNSSEC validation requirements. 

If this vulnerability had been exploited, it would not only result in the unavailability of DNS but also could have potential risks of disabling security mechanisms such as anti-spam defenses, Public Key Infrastructure (PKI), or even inter-domain routing security like RPKI (Resource Public Key Infrastructure).

Furthermore, a complete report about this vulnerability has been published by ATHENE researchers, which provides detailed information about the impact, attack types, vectors, and other information.

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