CVE-2025-4166 is a medium-severity vulnerability affecting HashiCorp Vault, specifically the Key/Value (kv) Version 2 plugin in both Vault Community and Enterprise editions. The vulnerability arises when users submit malformed payloads during secret creation or update operations via the Vault REST API. In such cases, Vault may inadvertently generate error messages that contain sensitive information. These error messages can be recorded in server and audit logs, potentially exposing confidential data to unauthorized parties who have access to these logs. The root cause relates to CWE-209, which concerns the generation of error messages containing sensitive information. This exposure could lead to information disclosure, undermining the confidentiality of secrets managed by Vault. The vulnerability affects versions starting from 0.3.0 and has been addressed in Vault Community 1.19.3 and Vault Enterprise versions 1.19.3, 1.18.9, 1.17.16, and 1.16.20. The CVSS 3.1 base score is 4.5, indicating a medium severity level. The vector indicates network attack vector (AV:N), low attack complexity (AC:L), but requires high privileges (PR:H) and user interaction (UI:R), with impact limited to confidentiality (C:H), no impact on integrity or availability. No known exploits are currently reported in the wild. This vulnerability is significant because Vault is widely used for secret management in enterprise environments, and leakage of sensitive information in logs could facilitate further attacks or data breaches if logs are not properly secured.

For European organizations, the impact of CVE-2025-4166 could be considerable, especially for those relying heavily on HashiCorp Vault for managing secrets, credentials, and sensitive configuration data. Exposure of sensitive information in logs could lead to unauthorized disclosure of secrets, potentially enabling attackers to escalate privileges, access protected systems, or exfiltrate data. This risk is heightened in environments where log access controls are weak or where logs are aggregated and analyzed by multiple teams or third-party services. Given the GDPR and other stringent data protection regulations in Europe, accidental exposure of sensitive information—even in logs—could result in compliance violations, reputational damage, and financial penalties. Additionally, organizations in sectors such as finance, healthcare, and critical infrastructure, which often use Vault for secure secret management, may face increased operational risks if attackers leverage leaked information to compromise systems. Although exploitation requires high privileges and user interaction, insider threats or compromised privileged accounts could trigger this vulnerability, making it a relevant concern for internal security policies.

European organizations should prioritize upgrading affected Vault instances to the patched versions: Vault Community 1.19.3 or Vault Enterprise 1.19.3, 1.18.9, 1.17.16, or 1.16.20. Beyond patching, organizations should implement strict access controls and monitoring on Vault server and audit logs to limit exposure of sensitive information. Logs should be encrypted at rest and in transit, and access should be restricted to authorized personnel only. It is advisable to review and sanitize logs regularly to detect and remove any sensitive data inadvertently logged. Organizations should also enforce the principle of least privilege to reduce the risk of high-privilege users triggering this vulnerability. Implementing robust input validation and error handling in client applications interacting with Vault can reduce the likelihood of malformed payloads causing sensitive error messages. Additionally, monitoring for unusual API usage patterns or malformed requests can help detect potential exploitation attempts. Finally, conducting regular security audits and penetration tests focused on secret management infrastructure will help identify and remediate similar issues proactively.