CVE-2025-40928 is a heap-based buffer overflow vulnerability identified in the Perl module JSON::XS, specifically in versions prior to 4.04. JSON::XS is a widely used Perl module designed for fast and efficient JSON parsing and encoding. The vulnerability arises from an integer buffer overflow during the parsing of specially crafted JSON input. This overflow can cause a segmentation fault (segfault), leading to a denial-of-service (DoS) condition. While the primary impact is a crash of the application using the vulnerable JSON::XS version, the nature of heap-based buffer overflows also raises concerns about potential memory corruption, which could be exploited for arbitrary code execution or other unspecified impacts, although no such exploits are currently known in the wild. The vulnerability is categorized under CWE-122, indicating a heap-based buffer overflow, which typically occurs when a program writes more data to a buffer located on the heap than it can hold, corrupting adjacent memory. The vulnerability was reserved in April 2025 and published in September 2025, but no patch links are currently available, suggesting that remediation may still be pending or in progress. Since JSON::XS is a core component in many Perl-based applications and services that handle JSON data, this vulnerability could affect a broad range of software systems that rely on Perl for data interchange, especially those processing untrusted JSON inputs.

For European organizations, the impact of CVE-2025-40928 can be significant, particularly for those relying on Perl-based applications for web services, data processing, or integration layers that consume JSON data. The immediate impact is denial-of-service, which can disrupt business operations, cause service outages, and degrade user experience. In critical infrastructure sectors such as finance, healthcare, telecommunications, and government services, such outages can lead to operational delays, loss of customer trust, and regulatory scrutiny. Additionally, the potential for memory corruption raises the risk of more severe exploitation, including unauthorized code execution, data breaches, or system compromise, which could lead to data loss or manipulation. Given the widespread use of JSON for data interchange, any service exposed to external or untrusted JSON inputs is at risk. European organizations with legacy Perl applications or those that have not updated JSON::XS to the latest version are particularly vulnerable. The lack of a patch at the time of publication increases the window of exposure, emphasizing the need for immediate risk mitigation.

European organizations should prioritize the following specific mitigation steps: 1) Inventory all Perl applications and services to identify usage of JSON::XS and determine the version in use. 2) Where possible, upgrade JSON::XS to version 4.04 or later once available, as this will contain the fix for the buffer overflow. 3) Until a patch is available, implement input validation and sanitization to restrict or reject untrusted or malformed JSON inputs that could trigger the overflow. 4) Employ runtime protections such as memory corruption mitigations (e.g., heap canaries, ASLR, DEP) at the operating system and application level to reduce exploitation risk. 5) Monitor application logs and system behavior for signs of crashes or unusual activity that could indicate exploitation attempts. 6) Consider isolating or sandboxing Perl applications that process external JSON data to limit the blast radius of potential attacks. 7) Engage with vendors or maintainers of Perl modules and dependent applications to track patch releases and security advisories. 8) Conduct penetration testing and fuzzing on JSON input handling to proactively identify and address similar vulnerabilities.