CVE-2024-3651 identifies a vulnerability in the kjd/idna library, version 3.6, within the idna.encode() function responsible for encoding internationalized domain names. The vulnerability is due to inefficient regular expression handling that results in quadratic computational complexity when processing specially crafted input strings. This inefficiency causes the function to consume excessive CPU resources, leading to a denial of service condition by significantly slowing down or halting the processing of requests. The vulnerability does not compromise confidentiality or integrity but affects availability by enabling an attacker to degrade service performance or cause application unresponsiveness. Exploitation requires local access to the vulnerable function but no special privileges or user interaction, making it a low-barrier attack vector in environments where the library is used. No patches have been published yet, and no known exploits are reported in the wild. The vulnerability is tracked under CWE-1333 (Inefficient Regular Expression Complexity), highlighting the root cause as poor input handling in regular expression processing. This issue is relevant for applications and services that rely on the kjd/idna library for domain name encoding, especially those exposed to untrusted input. Without mitigation, attackers can craft input strings that trigger the quadratic complexity, causing denial of service through resource exhaustion.

For European organizations, the primary impact of CVE-2024-3651 is on service availability. Applications or services that utilize the kjd/idna library for processing internationalized domain names may experience significant slowdowns or outages if exposed to crafted inputs exploiting this vulnerability. This can disrupt web services, DNS-related applications, or any software component relying on domain name encoding, potentially affecting customer-facing platforms or internal systems. The denial of service condition could lead to operational downtime, loss of productivity, and reputational damage. While the vulnerability does not expose sensitive data or allow unauthorized data modification, the availability impact can indirectly affect business continuity and user trust. Organizations with high volumes of domain name processing or those integrating this library into critical infrastructure are at greater risk. The lack of known exploits reduces immediate threat but does not eliminate the risk of future attacks once the vulnerability becomes widely known.

1. Monitor for official patches or updates from the kjd project and apply them promptly once available. 2. Until a patch is released, implement input validation to detect and reject suspicious or unusually long domain name inputs that could trigger the quadratic complexity. 3. Employ rate limiting and throttling on services that invoke the idna.encode() function to reduce the risk of resource exhaustion from repeated crafted inputs. 4. Consider sandboxing or isolating components that use the vulnerable library to limit the impact of potential denial of service. 5. Conduct code audits and testing to identify other potential inefficient regular expression usage in the codebase. 6. Maintain logging and monitoring to detect abnormal CPU usage or performance degradation indicative of exploitation attempts. 7. Educate developers and security teams about the risks of inefficient regex handling and encourage secure coding practices.