CVE-2025-66382 is a vulnerability identified in the libexpat XML parsing library, affecting versions through 2.7.3. The issue is classified under CWE-407, which relates to inefficient algorithmic complexity. Specifically, when libexpat processes a crafted XML file approximately 2 MiB in size, it can cause the parser to consume an excessive amount of processing time—dozens of seconds—due to suboptimal handling of certain XML structures. This results in a denial of service (DoS) condition by exhausting CPU resources, potentially impacting the availability of applications relying on libexpat for XML parsing. The CVSS v3.1 base score is 2.9, indicating low severity, with an attack vector of local (AV:L), high attack complexity (AC:H), no privileges required (PR:N), and no user interaction (UI:N). The vulnerability does not affect confidentiality or integrity, only availability. No known exploits have been reported in the wild, and no patches have been published yet. The vulnerability primarily impacts systems that parse XML files using libexpat, which is widely used in various open-source and commercial software. The lack of patches means organizations must rely on mitigating controls until an official fix is released.

For European organizations, the primary impact of CVE-2025-66382 is a potential denial of service caused by prolonged XML parsing times. This can degrade performance or cause service outages in applications that rely heavily on libexpat for XML processing, such as web servers, middleware, and embedded systems. Although the vulnerability requires local access and high attack complexity, insider threats or compromised internal systems could exploit it to disrupt services. Critical infrastructure sectors, including finance, telecommunications, and government services, which often process large XML data sets, may experience operational interruptions. The impact on confidentiality and integrity is negligible, but availability degradation could affect business continuity and user experience. Given the low CVSS score and no known exploits, the immediate risk is limited but should not be ignored, especially in environments with high XML processing loads or where service availability is critical.

To mitigate CVE-2025-66382, organizations should implement several practical measures beyond generic advice: 1) Monitor and limit the size and complexity of XML files accepted by applications using libexpat to prevent processing of excessively large or crafted files. 2) Employ input validation and XML schema enforcement to reject malformed or suspicious XML content early. 3) Use resource limiting techniques such as CPU time quotas or process isolation to contain the impact of prolonged parsing. 4) Consider deploying alternative XML parsers with better resilience to algorithmic complexity issues if feasible. 5) Stay informed about libexpat updates and apply patches promptly once available. 6) Conduct internal audits to identify systems using vulnerable libexpat versions and prioritize remediation in critical environments. 7) Implement logging and alerting for unusual XML processing delays to detect potential exploitation attempts. These steps help reduce the risk of denial of service and maintain service availability.