CVE-2025-13837 is a vulnerability identified in the plistlib module of CPython, the reference implementation of the Python programming language maintained by the Python Software Foundation. The plistlib module is used to parse plist (property list) files, which are commonly used for configuration and data storage, especially in macOS and iOS environments. The vulnerability stems from the module reading data sizes directly from the plist file without adequate validation or bounds checking. This allows an attacker to craft a malicious plist file that specifies an excessively large size for data to be read. When such a file is processed, the module attempts to allocate memory based on this size, potentially causing an out-of-memory (OOM) condition. This can lead to a denial of service (DoS) by crashing the Python process or severely degrading system performance. The CVSS 4.0 base score is 2.1, indicating low severity, with an attack vector of local (AV:L), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), and partial impact on availability (VA:L). No known exploits are currently in the wild, and no patches have been published at the time of disclosure. The vulnerability affects all versions of CPython that include the vulnerable plistlib implementation. Since plist files are often used in macOS/iOS contexts, but CPython is cross-platform, the vulnerability could affect any environment where Python scripts process plist files. The issue primarily impacts availability by enabling DoS via resource exhaustion, without affecting confidentiality or integrity.

For European organizations, the primary impact of CVE-2025-13837 is the potential for denial of service attacks against systems that utilize Python scripts or applications processing plist files. This could disrupt services, particularly in environments where Python is used for automation, configuration management, or data processing involving plist files. Organizations in sectors such as software development, telecommunications, and IT services that rely heavily on Python may experience operational interruptions. Although the vulnerability does not lead to data breaches or code execution, the resulting service outages could affect business continuity and availability of critical applications. The low severity and local attack vector mean that exploitation requires an attacker to have local access to the system or the ability to supply malicious plist files to vulnerable applications. This limits the scope but does not eliminate risk, especially in multi-user or shared environments. The absence of known exploits reduces immediate threat but does not preclude future exploitation. European organizations should be aware that any Python-based tooling or internal applications parsing plist files could be vectors for this DoS attack.

To mitigate CVE-2025-13837, European organizations should implement the following specific measures: 1) Audit and inventory all Python applications and scripts that utilize the plistlib module to identify potential exposure. 2) Restrict or sanitize input plist files, especially those originating from untrusted or external sources, by validating file sizes and content before processing. 3) Implement resource usage monitoring and limits (e.g., memory quotas) on processes handling plist files to detect and prevent excessive memory consumption. 4) Employ application-level sandboxing or containerization to isolate Python processes parsing plist files, limiting the impact of potential DoS. 5) Stay informed about updates from the Python Software Foundation and apply patches promptly once available. 6) Consider using alternative plist parsing libraries that perform stricter input validation if immediate patching is not feasible. 7) Educate developers and system administrators about the risks of processing untrusted plist files and encourage secure coding practices. These steps go beyond generic advice by focusing on input validation, resource control, and proactive patch management tailored to the specific nature of this vulnerability.