CVE-2025-0693 identifies a vulnerability in the AWS Sign-in IAM login flow where the response times vary depending on whether the IAM username exists or not. This timing discrepancy allows an unauthenticated attacker to perform brute force enumeration of valid IAM usernames within any AWS account. The vulnerability is categorized under CWE-204 (Observable Response Discrepancy) and CWE-208 (Information Exposure Through an Error Message or Other Information Leak). By measuring the time it takes for the login system to respond, an attacker can distinguish between valid and invalid usernames, thereby gaining sensitive information about the account's user base. This information leakage does not directly expose passwords or allow unauthorized access but significantly aids attackers in crafting targeted attacks such as phishing or password guessing. The vulnerability does not require any user interaction or privileges, making it accessible to remote attackers over the network. AWS has not indicated affected versions or released patches at the time of publication, and no known exploits have been observed in the wild. The CVSS v3.1 score of 5.3 reflects a medium severity, with a vector indicating network attack vector, low attack complexity, no privileges required, no user interaction, unchanged scope, and limited confidentiality impact. This vulnerability highlights the importance of uniform response times and error handling in authentication systems to prevent information leakage.

For European organizations, this vulnerability poses a risk primarily in the reconnaissance phase of an attack lifecycle. By enabling attackers to enumerate valid IAM usernames, it lowers the barrier for subsequent targeted attacks such as credential stuffing, phishing, or social engineering campaigns. Organizations heavily reliant on AWS IAM for managing cloud identities and access control could see increased attempts to compromise accounts once valid usernames are identified. While the vulnerability does not directly allow unauthorized access or disrupt services, the exposure of valid usernames can undermine security posture and increase the likelihood of successful breaches. This is particularly critical for sectors with sensitive data or critical infrastructure hosted on AWS, including finance, healthcare, and government entities in Europe. The lack of known exploits reduces immediate risk, but the ease of exploitation and the widespread use of AWS in Europe mean that attackers may develop exploits rapidly. Additionally, compliance with data protection regulations such as GDPR may be impacted if enumeration leads to unauthorized access or data breaches. Therefore, the vulnerability could indirectly affect confidentiality and organizational reputation.

European organizations should implement several specific measures to mitigate this vulnerability: 1) Monitor AWS CloudTrail and AWS IAM login logs for unusual login attempts or patterns indicative of brute force enumeration. 2) Enforce strict rate limiting and throttling on login attempts to reduce the feasibility of timing attacks. 3) Employ multi-factor authentication (MFA) universally to reduce the risk of account compromise even if usernames are enumerated. 4) Use AWS IAM Access Analyzer and AWS Config rules to audit and restrict permissions, minimizing the impact of any compromised accounts. 5) Encourage AWS to provide patches or updates addressing timing discrepancies and apply them promptly once available. 6) Implement uniform response times and generic error messages in custom authentication flows if applicable. 7) Conduct regular security awareness training to help users recognize phishing attempts that may follow username enumeration. 8) Consider deploying Web Application Firewalls (WAF) or Intrusion Detection Systems (IDS) with anomaly detection tuned to identify enumeration attempts. These steps go beyond generic advice by focusing on detection, prevention, and rapid response tailored to this specific timing-based enumeration threat.