Affected: WSO2 API Manager, WSO2 Identity Server as Key Manager, WSO2 Identity Server, WSO2 Open Banking IAM, WSO2 Open Banking AM, WSO2 Carborn Identity Handler

When a WSO2 product is configured to use an external user store, the system fails to adequately obscure the existence or validity of usernames during authentication attempts. This oversight allows an attacker to repeatedly query the authentication mechanism with different username guesses, enabling the enumeration of valid usernames present in the external user store.

The discovery of valid usernames can increase the risk of targeted brute-force attacks, social engineering, and information leakage. Attackers can leverage this information to craft more convincing phishing campaigns or other social engineering tactics to trick users into revealing sensitive data. The presence of username enumeration could also negatively impact an organization's reputation, leading to loss of customer trust, regulatory non-compliance, and potential legal and financial repercussions.