CVE-2025-55886 is an Insecure Direct Object Reference (IDOR) vulnerability identified in the ARD system, specifically within the payment history API endpoint. The vulnerability arises from improper access control on the `fe_uid` parameter, which is used to specify the user whose payment history is being requested. An authenticated attacker can manipulate this parameter to access payment histories of other users without proper authorization. This indicates a failure in enforcing authorization checks on user-specific data retrieval, allowing attackers to bypass intended access restrictions. The vulnerability requires the attacker to be authenticated, implying that it is not exploitable by unauthenticated users. However, once authenticated, the attacker can enumerate or guess other users' identifiers to retrieve sensitive financial transaction data. No affected versions or patches have been specified, and no known exploits are currently reported in the wild. The lack of a CVSS score suggests this is a recently disclosed vulnerability with limited public information. The core technical issue is the absence or misconfiguration of access control mechanisms validating that the requesting user is authorized to view the payment history associated with the `fe_uid` parameter. This type of vulnerability can lead to unauthorized disclosure of sensitive financial information, potentially enabling further attacks such as social engineering, fraud, or identity theft.

For European organizations using the ARD system, this vulnerability poses a significant risk to the confidentiality of customer financial data. Unauthorized access to payment histories can lead to privacy violations under GDPR, resulting in regulatory penalties and reputational damage. Financial institutions, e-commerce platforms, or any service handling payment data through ARD are particularly at risk. Attackers exploiting this flaw could harvest sensitive transaction details, which may be used for fraudulent activities or to compromise customer trust. The breach of payment history data could also facilitate targeted phishing or social engineering attacks against affected users. Additionally, organizations may face legal liabilities and customer attrition if such data exposure becomes public. The requirement for authentication limits the attack surface but does not eliminate the risk, especially if user credentials are compromised or if insider threats exist. The absence of patches or mitigations increases the urgency for affected organizations to implement compensating controls.

Organizations should immediately review and strengthen access control mechanisms on the payment history API endpoint. Specifically, the server-side logic must enforce strict authorization checks ensuring that the authenticated user can only access their own payment history corresponding to their user ID. Implementing parameter validation and user identity verification before data retrieval is critical. Employing role-based access control (RBAC) or attribute-based access control (ABAC) can help enforce these restrictions. Additionally, organizations should conduct thorough code audits and penetration testing focused on IDOR vulnerabilities across all APIs handling sensitive user data. Monitoring and logging access to payment history endpoints can help detect anomalous access patterns indicative of exploitation attempts. If patches become available, prompt application is essential. In the interim, organizations might consider rate limiting or anomaly detection to reduce the risk of mass enumeration attacks. Educating users on secure credential management and monitoring for compromised accounts can also reduce the risk of authenticated exploitation.