CVE-2023-50387 is a vulnerability rooted in the DNS Security Extensions (DNSSEC) protocol specifications defined in RFCs 4033, 4034, 4035, and 6840. The vulnerability, colloquially known as the "KeyTrap" issue, arises because DNSSEC validation requires verifying digital signatures (RRSIG records) against DNS public keys (DNSKEY records). When a DNS zone contains a large number of DNSKEY and RRSIG records, the protocol implies that the validation algorithm must evaluate all possible combinations of these records. This leads to a combinatorial explosion in computational effort, causing excessive CPU consumption on the validating resolver. An attacker can exploit this by sending malicious DNSSEC responses crafted to maximize the number of DNSKEY and RRSIG records, thereby triggering resource exhaustion and denial of service (DoS) conditions on DNS resolvers. The attack vector is remote and requires no authentication or user interaction, making it accessible to any attacker with network access to the target resolver. The vulnerability is classified under CWE-770 (Allocation of Resources Without Limits or Throttling), highlighting the lack of effective resource management in DNSSEC validation implementations. Although no specific affected products or versions are listed, any DNS resolver or validating server implementing DNSSEC according to the affected RFCs could be vulnerable. The CVSS v3.1 score of 7.5 (High) reflects the vulnerability's network attack vector, low complexity, no privileges required, no user interaction, and a significant impact on availability without affecting confidentiality or integrity. No patches or vendor advisories are currently linked, indicating that mitigation may rely on configuration changes or future updates.

For European organizations, the impact of CVE-2023-50387 can be substantial, particularly for those relying heavily on DNSSEC for domain name validation and security. DNS resolvers experiencing CPU exhaustion due to this vulnerability may become unresponsive or slow, leading to denial of service conditions that disrupt internet access and critical services dependent on DNS resolution. This can affect enterprises, ISPs, government agencies, and critical infrastructure providers, potentially causing widespread service outages. The disruption of DNS services can also impact email delivery, web services, and internal network operations. Since DNS is a foundational internet service, the ripple effects can degrade overall network reliability and trust in DNSSEC protections. The vulnerability's remote exploitability and lack of required privileges increase the risk of large-scale or targeted DoS attacks. European organizations with large DNS zones or those operating recursive resolvers validating DNSSEC signatures are at higher risk. Additionally, the vulnerability could be leveraged as part of multi-vector attacks against critical infrastructure, amplifying its impact.

To mitigate CVE-2023-50387, European organizations should: 1) Monitor DNS resolver logs for abnormal CPU usage or unusual DNSSEC response patterns indicative of exploitation attempts. 2) Limit the number of DNSKEY and RRSIG records accepted or processed per zone where possible, to reduce combinatorial complexity. 3) Employ rate limiting and query filtering on DNS resolvers to detect and block suspicious DNSSEC responses that could trigger resource exhaustion. 4) Update DNS resolver software to the latest versions as vendors release patches or optimizations addressing this vulnerability. 5) Consider deploying DNSSEC validation offloading or using hardened DNS resolver implementations known to handle large DNSSEC zones efficiently. 6) Collaborate with DNS zone administrators to minimize unnecessary DNSKEY and RRSIG records in zones under their control. 7) Implement network-level protections such as firewall rules and intrusion detection systems tuned to detect anomalous DNS traffic patterns. 8) Engage with DNS software vendors and security communities to stay informed about emerging fixes and best practices related to this vulnerability.