CVE-2024-3651 identifies a vulnerability in the kjd/idna library, specifically in the idna.encode() function of version 3.6. The root cause is inefficient handling of crafted input strings that causes the function to exhibit quadratic time complexity during processing. This inefficiency arises from the use of regular expressions that, when triggered by maliciously constructed input, require exponentially more computation as input size grows. The consequence is a denial of service (DoS) condition where the system’s CPU resources are heavily taxed, potentially leading to service unavailability. The vulnerability does not compromise confidentiality or integrity but impacts availability significantly. Exploitation requires local access (AV:L), no privileges (PR:N), and no user interaction (UI:N), meaning an attacker with local access can trigger the DoS without elevated permissions or user involvement. The vulnerability is categorized under CWE-1333, which relates to inefficient regular expression complexity. No patches or fixes are currently linked, and no known exploits have been reported in the wild. The CVSS v3.0 score is 6.2, indicating a medium severity level, with the vector AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. This means the attack vector is local, attack complexity is low, no privileges or user interaction are required, and the impact is on availability only. Organizations using kjd/idna for processing internationalized domain names or related functions should be aware of this vulnerability and monitor for updates or patches.

The primary impact of CVE-2024-3651 is denial of service due to excessive CPU consumption when processing crafted input strings in the kjd/idna library. For European organizations, this can lead to service outages or degraded performance in applications relying on this library for domain name processing, such as web servers, email systems, or DNS-related services. Availability disruptions can affect business continuity, customer trust, and operational efficiency. Since the vulnerability requires local access, the risk is higher in environments where untrusted users have local system access or where multi-tenant systems share resources. The lack of confidentiality or integrity impact limits data breach risks, but availability issues can still cause significant operational and reputational damage. Organizations in sectors with critical internet infrastructure or heavy use of internationalized domain names, such as telecommunications, finance, and government, may experience more severe consequences. The absence of known exploits reduces immediate risk but does not eliminate the threat, especially if attackers develop local access methods or combine this vulnerability with other attack vectors.

1. Monitor for and apply official patches or updates from the kjd project as soon as they become available to address the inefficient regular expression handling. 2. Implement input validation to detect and reject unusually long or suspiciously crafted domain name strings before they reach the idna.encode() function. 3. Apply rate limiting and resource usage controls on services that invoke kjd/idna to prevent CPU exhaustion from repeated or large input processing. 4. Restrict local access to systems running vulnerable versions of kjd/idna to trusted users only, minimizing the risk of exploitation. 5. Employ application-level sandboxing or containerization to isolate processes using kjd/idna, limiting the impact of potential DoS conditions. 6. Conduct code audits and dependency reviews to identify where kjd/idna is used and assess exposure. 7. Consider fallback or alternative libraries for internationalized domain name processing if patching is delayed. 8. Enhance monitoring and alerting for unusual CPU usage patterns that may indicate exploitation attempts.