CVE-2024-12243 identifies a vulnerability in the GnuTLS library stemming from an inefficient algorithmic complexity issue within the libtasn1 ASN.1 parsing component. GnuTLS relies on libtasn1 to decode DER-encoded ASN.1 certificate data during TLS handshake processes. The flaw arises because certain crafted DER certificates cause the libtasn1 decoder to perform excessive computation, consuming disproportionate CPU resources and causing the GnuTLS process to become unresponsive or significantly slowed. This results in a denial-of-service condition, as the affected service cannot timely complete TLS handshakes or maintain normal operation. The vulnerability affects GnuTLS versions 0 through 3.8.0, with no authentication or user interaction required for exploitation, and can be triggered remotely by an attacker presenting a malicious certificate during TLS negotiation. The CVSS v3.1 base score is 5.3 (medium), reflecting the lack of impact on confidentiality or integrity but a clear impact on availability. No public exploits have been reported yet, but the potential for DoS attacks on servers or clients using vulnerable GnuTLS versions is significant. The vulnerability highlights the risks of algorithmic complexity attacks in cryptographic libraries, emphasizing the need for efficient parsing algorithms and resource usage controls. As GnuTLS is widely used in open-source projects, Linux distributions, and embedded systems, the scope of affected systems is broad, especially in environments relying on open-source TLS implementations.

For European organizations, the primary impact of CVE-2024-12243 is the potential for denial-of-service attacks against services using vulnerable GnuTLS versions. This can disrupt web servers, mail servers, VPN gateways, and other network services that rely on GnuTLS for secure communications. The unavailability of these services can lead to operational downtime, loss of customer trust, and potential financial losses. Critical infrastructure sectors such as telecommunications, finance, and government services that depend on open-source TLS libraries may experience service degradation or outages. Since the vulnerability does not compromise data confidentiality or integrity, the risk is limited to availability. However, the ease of remote exploitation without authentication increases the threat level, especially for internet-facing services. Organizations with high traffic volumes or those exposed to untrusted networks are at greater risk of resource exhaustion attacks. The lack of known exploits currently provides a window for proactive mitigation, but attackers may develop exploits given the public disclosure.

European organizations should prioritize updating GnuTLS to versions beyond 3.8.0 once patches are released by maintainers or distributions. Until patches are available, administrators can implement rate limiting and connection throttling on TLS endpoints to reduce the impact of resource exhaustion. Deploying Web Application Firewalls (WAFs) or network-level DoS protection can help detect and block suspicious certificate negotiation attempts. Monitoring CPU and memory usage on critical servers can provide early warning signs of exploitation attempts. Where feasible, consider using alternative TLS libraries not affected by this vulnerability for critical services. Additionally, organizations should audit their software dependencies to identify all instances of GnuTLS usage, including embedded systems and containers, to ensure comprehensive coverage. Security teams should update incident response plans to include detection and mitigation strategies for algorithmic complexity DoS attacks. Finally, engaging with Linux distribution security advisories and applying vendor patches promptly will minimize exposure.