CVE-2025-35940 is a high-severity vulnerability affecting GFI Archiver version 15.7, specifically within its ArchiverSpaApi ASP.NET application. The core issue is the use of a hard-coded JWT (JSON Web Token) signing key embedded in the application code. JWTs are commonly used for authentication and authorization by signing tokens with a secret key to ensure their integrity and authenticity. However, when the signing key is hard-coded and not dynamically generated or securely stored, it becomes a critical security weakness. An unauthenticated remote attacker can exploit this vulnerability by generating their own JWT tokens signed with the known hard-coded key. These forged tokens will be accepted as valid by the ArchiverSpaApi endpoints, granting unauthorized access to protected resources and functionality. This bypasses authentication controls entirely, allowing attackers to perform actions with potentially elevated privileges. The vulnerability impacts confidentiality, integrity, and availability since attackers can access sensitive data, modify or delete information, and disrupt normal operations. The CVSS 3.1 score of 8.1 reflects the network exploitable nature (AV:N), no privileges required (PR:N), no user interaction (UI:N), and high impact on confidentiality, integrity, and availability (C:H/I:H/A:H). Although no public exploits are currently known, the simplicity of generating valid JWT tokens using the hard-coded key makes exploitation feasible. This vulnerability is categorized under CWE-798 (Use of Hard-coded Credentials), a common and dangerous security flaw in software development that undermines authentication mechanisms.

For European organizations using GFI Archiver 15.7, this vulnerability poses a significant risk. Unauthorized access to ArchiverSpaApi endpoints can lead to exposure of sensitive archived emails and documents, potentially including personal data protected under GDPR. Attackers could manipulate or delete archived records, impacting data integrity and compliance. The ability to bypass authentication without user interaction increases the risk of automated or large-scale attacks. Organizations relying on GFI Archiver for regulatory compliance, e-discovery, or data retention may face operational disruptions and legal consequences if this vulnerability is exploited. The breach of confidentiality could also damage organizational reputation and trust. Given the critical role of email archiving in many European enterprises, especially in finance, legal, healthcare, and government sectors, the impact could be severe.

To mitigate this vulnerability, organizations should immediately upgrade to a patched version of GFI Archiver once available, as no patch links are currently provided. In the interim, restrict network access to the ArchiverSpaApi endpoints using firewall rules or network segmentation to limit exposure to trusted internal IPs only. Implement Web Application Firewall (WAF) rules to detect and block suspicious JWT tokens or anomalous API requests. Conduct a thorough audit of existing JWT tokens and revoke any that may have been compromised. Review and enhance application security practices by eliminating hard-coded credentials and adopting secure key management solutions such as environment variables, secure vaults, or hardware security modules (HSMs). Monitor logs for unusual access patterns or failed authentication attempts. Additionally, consider deploying multi-factor authentication (MFA) on management interfaces and sensitive endpoints to add an extra layer of defense. Finally, educate development teams on secure coding practices to prevent recurrence of hard-coded secrets.