CVE-2026-25210 is a vulnerability classified under CWE-190 (Integer Overflow or Wraparound) affecting the libexpat XML parsing library before version 2.7.4. The issue arises in the doContent function, which is responsible for processing XML content. Specifically, the function fails to properly check for integer overflow when calculating the buffer size (bufSize) needed for tag buffer reallocation. Without this check, an attacker can craft XML input that triggers an integer overflow, causing the buffer size to wrap around to a smaller value than intended. This miscalculation can lead to buffer overflows during memory operations, potentially allowing memory corruption. The consequences include arbitrary code execution or denial of service due to application crashes. The vulnerability requires local access (Attack Vector: Local) and has a high attack complexity, meaning exploitation is non-trivial and likely requires detailed knowledge of the target environment. No privileges or user interaction are needed, but the attacker must have the ability to supply malicious XML input to the vulnerable libexpat instance. The vulnerability affects all versions of libexpat prior to 2.7.4, a widely used XML parsing library embedded in many software products and systems. Although no public exploits are known at this time, the vulnerability poses a significant risk due to the potential for high confidentiality and integrity impact. The CVSS v3.1 base score is 6.9, indicating a medium severity level. The vulnerability was published on January 30, 2026, and no official patches or exploit mitigations are linked yet, so users should monitor vendor updates closely.

For European organizations, the impact of CVE-2026-25210 can be substantial, especially for those relying on libexpat in critical applications such as web servers, XML processing tools, middleware, and embedded systems. Successful exploitation could lead to unauthorized disclosure of sensitive information (confidentiality impact) or unauthorized modification of data (integrity impact). The potential for denial of service, while lower, could disrupt business operations. Given libexpat's widespread use in open-source and commercial software, many European enterprises, including financial institutions, government agencies, and technology providers, could be affected. The requirement for local access and high attack complexity somewhat limits the attack surface, but insider threats or compromised internal systems could exploit this vulnerability. The lack of user interaction and privileges needed means automated or scripted attacks in controlled environments are feasible once local access is obtained. The vulnerability could also affect supply chain security if software vendors or integrators use vulnerable libexpat versions, potentially impacting downstream customers across Europe.

European organizations should immediately inventory all software and systems using libexpat to identify vulnerable versions prior to 2.7.4. Until official patches are released, consider applying temporary mitigations such as restricting local access to systems running libexpat, enforcing strict input validation and sanitization on XML data, and employing runtime protections like memory safety tools (e.g., AddressSanitizer) to detect buffer overflows. Software vendors and integrators should prioritize upgrading libexpat to version 2.7.4 or later as soon as it becomes available. Additionally, organizations should monitor security advisories from the libexpat project and related software vendors for patches or workarounds. Implementing strict access controls and monitoring for anomalous local activity can reduce the risk of exploitation. For critical systems, consider isolating XML processing components or running them with least privilege to limit potential damage. Finally, conduct security testing and code audits on applications using libexpat to identify and remediate any related vulnerabilities.