CVE-2026-53908 in MCO
Summary
by MITRE • 07/01/2026
MCO is vulnerable to User Enumeration through authentication-related functionalities. The application returns distinguishable responses for valid and invalid users during username reminder and password reset operations. An attacker can leverage these differences to enumerate valid usernames and email addresses.
Because vendor contact attempts were unsuccessful, the vulnerability has only been confirmed in version 25.3.3.1 but may also affect other versions.
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Analysis
by VulDB Data Team • 07/01/2026
This vulnerability represents a critical user enumeration flaw that undermines the security posture of the MCO application through improper authentication response handling. The issue manifests during username reminder and password reset functionalities where the system provides distinguishable responses for valid versus invalid user accounts. This behavior creates a clear information disclosure channel that allows attackers to systematically identify legitimate user credentials through automated probing techniques.
The technical implementation flaw stems from inadequate input validation and response normalization within the authentication workflow. When users attempt to access username reminder or password reset features, the application's backend logic fails to provide consistent error messaging regardless of whether the provided identifier corresponds to an existing account. This inconsistency enables attackers to differentiate between valid and invalid usernames through response timing variations, HTTP status codes, or message content differences that reveal account existence.
From an operational impact perspective, this vulnerability significantly increases the attack surface for credential-based attacks including brute force attempts, social engineering campaigns, and account takeover operations. The enumeration capability allows threat actors to build comprehensive user directories that can then be leveraged for targeted attacks against specific individuals within the organization. This issue directly aligns with CWE-204 which addresses information exposure through response differences and maps to ATT&CK technique T1078.101 related to valid accounts for credential access.
The vulnerability's exploitation potential is amplified by the fact that attackers can combine enumeration results with other reconnaissance techniques to build targeted attack profiles. Once valid usernames are identified, attackers can proceed with password spraying, credential stuffing, or more sophisticated social engineering approaches. The lack of vendor confirmation beyond version 25.3.3.1 suggests this may be a widespread issue affecting multiple versions, making it particularly concerning for organizations that have not yet updated their systems.
Security mitigations should focus on implementing consistent response handling across all authentication-related functions to eliminate distinguishable responses for valid and invalid users. Organizations must ensure that username reminder and password reset operations return identical responses regardless of account existence, effectively neutralizing the enumeration capability. Additionally, rate limiting and account lockout mechanisms should be implemented to prevent automated enumeration attempts, while monitoring systems should be configured to detect unusual patterns of authentication requests that may indicate probing activities. The remediation approach should align with industry best practices for secure authentication design as outlined in NIST SP 800-63B and OWASP authentication security guidelines.