CVE-2021-46143 is a high-severity integer overflow vulnerability found in the doProlog function within the xmlparse.c source file of the Expat XML parsing library (also known as libexpat) in versions prior to 2.4.3. The vulnerability arises due to an integer overflow condition affecting the variable m_groupSize, which is used internally during XML parsing. Integer overflow occurs when an arithmetic operation attempts to create a numeric value that is outside the range that can be represented with a given number of bits, causing the value to wrap around unexpectedly. In this context, the overflow can lead to improper memory allocation or buffer size calculations, potentially resulting in heap-based buffer overflows or memory corruption. Such memory corruption can be exploited by attackers to execute arbitrary code, cause denial of service (application crashes), or manipulate the integrity of the XML parsing process. The vulnerability does not require user interaction or privileges to exploit, but it does require the attacker to supply crafted XML data to the vulnerable parser. The CVSS 3.1 base score of 8.1 reflects the high impact on confidentiality, integrity, and availability, with a network attack vector and high complexity (AC:H) due to the need for precise crafted input. No known exploits in the wild have been reported to date, but the vulnerability is critical given the widespread use of libexpat in many software projects and systems for XML processing. The vulnerability is tracked under CWE-190 (Integer Overflow or Wraparound). No official patch links were provided in the source, but upgrading to Expat version 2.4.3 or later is recommended as it addresses this issue.

For European organizations, the impact of CVE-2021-46143 can be significant due to the pervasive use of libexpat in numerous applications, middleware, and embedded systems that process XML data. Exploitation could lead to remote code execution or denial of service in critical infrastructure, enterprise software, web services, and industrial control systems that rely on XML parsing. Confidentiality could be compromised if attackers leverage the vulnerability to execute arbitrary code and access sensitive data. Integrity risks arise from potential manipulation of XML content or application behavior. Availability may be affected through crashes or service disruptions. Given the high CVSS score and no requirement for authentication or user interaction, attackers could remotely exploit vulnerable systems by sending malicious XML payloads. This is particularly concerning for sectors such as finance, healthcare, telecommunications, and government agencies in Europe, where XML-based communication and data exchange are common. The lack of known exploits in the wild reduces immediate risk but does not eliminate the threat, especially as attackers often develop exploits after vulnerability disclosure. Organizations using software that bundles libexpat should assess their exposure and prioritize remediation to prevent potential exploitation.

1. Upgrade libexpat to version 2.4.3 or later, where this integer overflow vulnerability has been fixed. 2. Identify all software and systems within the organization that use libexpat for XML parsing, including third-party applications and embedded devices, and verify their versions. 3. If immediate upgrade is not feasible, implement network-level protections such as input validation and filtering to block or sanitize suspicious XML payloads from untrusted sources. 4. Employ runtime protections like Address Space Layout Randomization (ASLR), Data Execution Prevention (DEP), and Control Flow Integrity (CFI) to mitigate exploitation impact. 5. Monitor logs and network traffic for anomalous XML parsing errors or crashes that could indicate exploitation attempts. 6. Coordinate with software vendors to obtain patches or updates for products that embed vulnerable versions of libexpat. 7. Conduct penetration testing and vulnerability scanning focused on XML processing components to detect presence of the vulnerability. 8. Maintain an incident response plan that includes procedures for handling exploitation of XML parser vulnerabilities.