CVE-2025-40929 identifies a heap-based buffer overflow vulnerability in the Perl module Cpanel::JSON::XS, maintained by the RURBAN project. This module is widely used for fast and efficient JSON parsing in Perl applications. The vulnerability stems from an integer overflow during buffer allocation when parsing crafted JSON data, leading to a segmentation fault (segfault). This segfault can be triggered remotely by sending malicious JSON payloads to applications using vulnerable versions of Cpanel::JSON::XS (versions before 4.40). The consequence is primarily a denial-of-service (DoS) condition, where the application crashes, disrupting service availability. The CVSS v3.1 score is 5.6 (medium severity), reflecting network attack vector, no privileges required, no user interaction, but high attack complexity. Although the primary impact is DoS, the nature of heap buffer overflows could allow other unspecified impacts, potentially including memory corruption or code execution, though no such exploits are currently known. The vulnerability affects all deployments using the vulnerable module version, especially those parsing untrusted JSON input. No official patches were linked at the time of publication, but upgrading to version 4.40 or later is recommended once available. The vulnerability was reserved in April 2025 and published in September 2025, indicating recent discovery and disclosure.

For European organizations, the primary impact is service disruption due to denial-of-service attacks targeting applications that use vulnerable versions of Cpanel::JSON::XS for JSON parsing. This can affect web services, APIs, or backend systems relying on Perl modules for data interchange. Organizations in sectors such as finance, government, telecommunications, and critical infrastructure that utilize Perl-based applications could face operational downtime, impacting business continuity and customer trust. Although no known exploits exist, the potential for attackers to craft malicious JSON payloads remotely without authentication increases risk exposure. Additionally, if the vulnerability is leveraged for memory corruption beyond DoS, it could lead to data integrity issues or unauthorized code execution, further elevating the threat. The medium severity rating suggests moderate risk, but the widespread use of JSON and Perl in enterprise environments means the attack surface is significant. European entities with legacy systems or delayed patching cycles are particularly vulnerable.

1. Upgrade Cpanel::JSON::XS to version 4.40 or later as soon as the patch is available to eliminate the integer buffer overflow vulnerability. 2. Implement strict input validation and sanitization for all JSON data received from untrusted sources to reduce the risk of malicious payloads triggering the overflow. 3. Employ application-layer sandboxing or containerization to isolate JSON parsing components, limiting the blast radius of potential crashes or exploits. 4. Monitor application logs and network traffic for unusual JSON parsing errors or crashes that could indicate exploitation attempts. 5. Conduct code audits and penetration testing focusing on JSON handling routines in Perl applications to identify and remediate similar vulnerabilities. 6. Maintain an up-to-date inventory of Perl modules and dependencies to ensure timely patch management. 7. Consider deploying Web Application Firewalls (WAFs) with custom rules to detect and block suspicious JSON payloads targeting this vulnerability. 8. Educate developers and system administrators about secure JSON parsing practices and the importance of timely updates.