CVE-2022-25313 is a vulnerability identified in the Expat XML parser library (libexpat) versions prior to 2.4.5. The issue arises from the way Expat processes Document Type Definition (DTD) elements with deeply nested structures. Specifically, an attacker can craft an XML input containing a DTD with an excessively large nesting depth, which triggers stack exhaustion in the build_model function. This stack exhaustion occurs because the recursive parsing of nested DTD elements consumes stack memory without adequate bounds checking or limits, leading to a denial-of-service (DoS) condition. The vulnerability does not impact confidentiality or integrity directly but affects availability by causing the affected application or service using libexpat to crash or become unresponsive. The CVSS v3.1 base score is 6.5 (medium severity), reflecting that the attack can be launched remotely (AV:N), requires no privileges (PR:N), but does require user interaction (UI:R), and impacts availability (A:H) without affecting confidentiality or integrity. No known exploits are currently reported in the wild, and no specific patches or vendor information are provided in the data. The underlying weakness is classified under CWE-674: Uncontrolled Recursion, which highlights the risk of stack exhaustion due to unbounded recursive calls. Since libexpat is widely used in many software products and systems for XML parsing, this vulnerability could potentially affect a broad range of applications that process XML input, especially those that accept untrusted XML data containing DTDs.

For European organizations, the primary impact of CVE-2022-25313 is the risk of denial-of-service attacks against applications and services that rely on vulnerable versions of libexpat for XML parsing. This can disrupt business operations, especially in sectors where XML is heavily used for data interchange, such as finance, telecommunications, government services, and industrial control systems. The DoS condition could lead to service outages, degraded performance, or application crashes, impacting availability and potentially causing operational downtime. Since the vulnerability requires user interaction (e.g., processing a crafted XML file or message), threat actors might exploit it via phishing emails, malicious uploads, or network-based XML payloads. Although no direct data breach or integrity compromise is indicated, the availability impact can indirectly affect compliance with regulations such as GDPR if services become unavailable or data processing is interrupted. Additionally, organizations relying on third-party software embedding libexpat may face challenges in identifying and patching affected components promptly. The absence of known exploits reduces immediate risk but does not eliminate the threat, especially as attackers may develop exploits over time.

European organizations should take the following specific mitigation steps: 1) Inventory and identify all software and systems that use libexpat for XML parsing, including embedded devices and third-party applications. 2) Upgrade libexpat to version 2.4.5 or later, where the vulnerability is fixed. If direct upgrades are not feasible, apply vendor patches or updates that include the fixed libexpat version. 3) Implement input validation and XML parsing restrictions, such as disabling DTD processing or limiting the maximum allowed nesting depth of XML elements, to prevent exploitation via maliciously crafted XML. 4) Employ application-layer firewalls or XML gateways that can detect and block suspicious XML payloads with excessive nesting or large DTDs. 5) Monitor application logs and network traffic for unusual XML processing errors or crashes that may indicate attempted exploitation. 6) Educate users and administrators about the risks of processing untrusted XML files and the importance of applying security updates promptly. 7) For critical systems, consider sandboxing XML parsing operations to contain potential DoS effects. These targeted measures go beyond generic patching advice by focusing on detection, prevention, and operational controls tailored to the nature of this vulnerability.