CVE-2025-63917 identifies a critical XML External Entity (XXE) vulnerability in PDFPatcher, a tool used for managing PDF bookmarks. The vulnerability exists because the application uses the .NET XmlDocument class to parse XML bookmark imports without disabling the resolution of external entities. This improper configuration allows attackers to craft malicious XML files containing external entity references. When such a file is imported, the application processes these entities, enabling several attack vectors: reading arbitrary files on the host system, exfiltrating sensitive data through out-of-band (OOB) HTTP requests to attacker-controlled servers, conducting SSRF attacks to access internal network resources that are otherwise inaccessible externally, and causing denial of service via entity expansion attacks (billion laughs or similar). The vulnerability is exploitable remotely over the network without authentication but requires user interaction to import the malicious XML. The CVSS v3.1 base score is 7.1, reflecting high confidentiality impact, low attack complexity, no privileges required, and user interaction needed. No patches or exploits are currently publicly known, but the risk is significant given the sensitive nature of data potentially exposed and the common use of .NET XML parsers. The CWE-611 classification confirms this as an XXE issue. Organizations relying on PDFPatcher for document processing should consider this vulnerability critical and act accordingly.

For European organizations, the impact of CVE-2025-63917 can be substantial, particularly in sectors such as finance, legal, government, and healthcare where PDF documents often contain sensitive or confidential information. Exploitation could lead to unauthorized disclosure of sensitive files, potentially violating data protection regulations like GDPR. SSRF capabilities could allow attackers to pivot into internal networks, accessing otherwise protected resources, increasing the risk of lateral movement and further compromise. Denial of service attacks could disrupt business operations reliant on PDFPatcher for document workflows. Since the vulnerability requires user interaction, phishing or social engineering campaigns could be used to trick employees into importing malicious XML files, increasing the attack surface. The lack of known exploits in the wild currently reduces immediate risk but does not eliminate the threat, especially as proof-of-concept exploits may emerge. The high confidentiality impact combined with the potential for internal network compromise makes this vulnerability a serious concern for European enterprises.

Immediate mitigation steps include disabling external entity resolution in the XML parser used by PDFPatcher. For .NET applications, this involves configuring XmlReaderSettings or XmlDocument to prohibit DTD processing and external entity resolution. Organizations should audit their use of PDFPatcher and restrict the import of XML bookmarks to trusted sources only. Employing network-level controls to block outbound HTTP requests to untrusted domains can limit data exfiltration via OOB channels. Monitoring and alerting on unusual outbound traffic patterns can help detect exploitation attempts. Until an official patch is released, consider isolating PDFPatcher usage to segmented environments with limited access to sensitive data and internal networks. User education to recognize suspicious files and avoid importing untrusted XML bookmarks is critical. Finally, maintain up-to-date backups and incident response plans to quickly recover from potential denial of service or data breaches.