CVE-2021-37151 in Identity
Summary
by MITRE • 09/01/2021
CyberArk Identity 21.5.131, when handling an invalid authentication attempt, sometimes reveals whether the username is valid. In certain authentication policy configurations with MFA, the API response length can be used to differentiate between a valid user and an invalid one (aka Username Enumeration). Response differentiation enables attackers to enumerate usernames of valid application users. Attackers can use this information to leverage brute-force and dictionary attacks in order to discover valid account information such as passwords.
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Analysis
by VulDB Data Team • 09/04/2021
The vulnerability identified as CVE-2021-37151 affects CyberArk Identity version 21.5.131 and represents a critical username enumeration flaw that undermines the security of authentication systems. This issue manifests when the system processes invalid authentication attempts and inadvertently provides different response characteristics based on whether the submitted username exists within the system. The vulnerability specifically occurs in certain authentication policy configurations that incorporate multi-factor authentication mechanisms, creating a scenario where attackers can exploit subtle differences in API response lengths to determine valid user accounts.
The technical implementation of this vulnerability stems from the inconsistent handling of authentication responses across different user states. When a user attempts authentication with an invalid username, the system's response length varies depending on whether the username exists in the directory. This differential response behavior creates a timing and length-based side-channel attack vector that allows adversaries to systematically test usernames and observe response characteristics to distinguish between valid and invalid accounts. The vulnerability is particularly concerning because it operates at the API level, making it accessible through automated tools and scripts that can rapidly enumerate valid usernames.
The operational impact of this vulnerability extends beyond simple username discovery, as it provides attackers with the foundational information necessary for more sophisticated attacks. Once valid usernames are identified through enumeration, threat actors can conduct targeted brute-force and dictionary attacks against these accounts, significantly increasing their success rate compared to random guessing. The vulnerability affects the core authentication infrastructure, potentially compromising the entire user base of applications integrated with CyberArk Identity, especially when MFA is configured in a way that allows this enumeration to occur. This weakness undermines the fundamental security principle of authentication systems that should not reveal information about account existence to unauthorized parties.
Security practitioners should implement multiple mitigations to address this vulnerability, beginning with configuration changes that ensure consistent response handling regardless of user account status. The most effective approach involves standardizing API response lengths and timing characteristics for all authentication attempts, eliminating the side-channel information that enables enumeration. Organizations should also implement account lockout mechanisms, rate limiting, and monitoring for unusual authentication patterns to detect and prevent automated enumeration attempts. Additionally, the principle of least privilege should be enforced to ensure that authentication systems do not provide information that could aid attackers in compromising user accounts. This vulnerability aligns with CWE-200, which addresses information exposure, and maps to ATT&CK technique T1078 for valid accounts and T1110 for brute force attacks, emphasizing the need for comprehensive defensive measures that address both the immediate vulnerability and its potential exploitation pathways.