CVE-2021-40693 in Moodle
Summary
by MITRE • 09/29/2022
An authentication bypass risk was identified in the external database authentication functionality, due to a type juggling vulnerability.
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Analysis
by VulDB Data Team • 10/25/2022
The vulnerability identified as CVE-2021-40693 represents a critical authentication bypass flaw within external database authentication systems that leverages type juggling vulnerabilities to circumvent security controls. This weakness exists in the way the system processes authentication credentials when interacting with external databases, creating a pathway for unauthorized access that directly undermines the fundamental security premise of authentication mechanisms. The issue manifests when the application performs implicit type conversions during authentication validation, allowing maliciously crafted input to be interpreted in unexpected ways that bypass intended security checks.
This vulnerability operates through type juggling techniques that exploit PHP's loose comparison operators, where the system fails to properly validate or sanitize input parameters before processing them in authentication contexts. When legitimate authentication credentials are submitted, the application's handling of these inputs through loose type comparisons creates opportunities for attackers to manipulate the authentication flow by providing specially crafted data that evaluates to true under PHP's type coercion rules. The flaw specifically affects the external database authentication functionality, suggesting that the vulnerability is present in how the system interfaces with external authentication sources rather than internal authentication mechanisms.
The operational impact of this vulnerability is severe as it allows attackers to bypass authentication entirely without requiring valid credentials, potentially granting access to sensitive database resources, user accounts, and system functionalities. An attacker exploiting this vulnerability could gain unauthorized access to external databases, leading to data breaches, privilege escalation, and potential lateral movement within network environments. The attack vector typically involves crafting malicious input that triggers the type juggling behavior, potentially through API calls, web forms, or direct database connection attempts. This vulnerability directly violates the principle of least privilege and undermines the integrity of the authentication system, creating persistent access opportunities for threat actors.
Mitigation strategies should focus on implementing strict type checking mechanisms, avoiding loose comparison operators in authentication contexts, and ensuring proper input validation and sanitization before any authentication processing occurs. Organizations should update their authentication modules to use strict comparison operators, implement proper parameter validation, and conduct thorough code reviews to identify similar type juggling vulnerabilities. The fix should include explicit type casting, input sanitization, and comprehensive testing of authentication flows to prevent similar issues. This vulnerability aligns with CWE-691, which addresses insufficient type checking, and maps to ATT&CK technique T1110.003 for credential access through password guessing and bypass methods. Security teams should prioritize patching affected systems and implementing monitoring for suspicious authentication patterns that could indicate exploitation attempts.