CVE-2024-12243 is a vulnerability identified in the GnuTLS library, which is widely used for implementing SSL/TLS protocols in various software applications. The root cause of this vulnerability lies in libtasn1, a library that GnuTLS depends on for processing ASN.1 data structures, specifically DER-encoded certificate data. The flaw is due to an inefficient algorithmic complexity in libtasn1's decoding process. When a specially crafted DER-encoded certificate is processed, the decoding operation can consume excessive CPU resources and time, causing GnuTLS to become unresponsive or significantly slow down. This behavior can be exploited remotely by an attacker who sends maliciously crafted certificates during TLS handshakes or other certificate validation processes, leading to a denial-of-service (DoS) condition. The vulnerability affects GnuTLS versions 0, 3.7.0, and 3.8.0, and does not require any authentication or user interaction to be exploited. The CVSS v3.1 base score is 5.3, indicating a medium severity level, with the vector AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L, meaning the attack can be launched remotely over the network with low complexity, no privileges or user interaction needed, and impacts availability only. No known exploits are reported in the wild as of the publication date. This vulnerability is significant because GnuTLS is embedded in many Linux distributions, network appliances, and security-sensitive applications, making it a potential vector for service disruption in environments relying on TLS communications.

For European organizations, the impact of CVE-2024-12243 can be substantial, especially for those relying on GnuTLS for secure communications in critical infrastructure, financial services, government, and telecommunications sectors. A successful exploitation could lead to denial-of-service conditions on servers or network devices that perform TLS handshakes, potentially disrupting secure communications and causing service outages. This can affect web servers, VPN gateways, mail servers, and other TLS-dependent services. The unavailability of these services can result in operational downtime, loss of customer trust, and potential regulatory non-compliance, particularly under GDPR and other data protection laws that mandate availability and integrity of services. Additionally, the increased resource consumption could be leveraged as part of a larger distributed denial-of-service (DDoS) attack, amplifying its impact. While the vulnerability does not compromise confidentiality or integrity, the availability impact alone can be critical for high-availability environments common in European enterprises and public sector organizations.

To mitigate this vulnerability, European organizations should prioritize updating GnuTLS and libtasn1 libraries to versions where this inefficiency is resolved. Since no patch links are provided in the source, organizations should monitor official GnuTLS and libtasn1 repositories and security advisories for patches or updates addressing CVE-2024-12243. In the interim, organizations can implement network-level protections such as rate limiting and deep packet inspection to detect and block anomalous TLS handshake attempts with suspicious certificate data. Deploying Web Application Firewalls (WAFs) or Intrusion Prevention Systems (IPS) with custom rules to identify and drop malformed or unusually large certificate payloads can reduce exposure. Additionally, logging and monitoring TLS handshake failures and resource usage spikes on servers can help detect exploitation attempts early. Organizations should also review and harden their TLS configurations to minimize exposure, including disabling unnecessary services using GnuTLS and considering alternative TLS libraries if feasible. Finally, conducting penetration testing and resilience assessments simulating this attack vector can help validate defenses.