CVE-2018-20170 in OpenStack Keystone
Summary
by MITRE
** DISPUTED ** OpenStack Keystone through 14.0.1 has a user enumeration vulnerability because invalid usernames have much faster responses than valid ones for a POST /v3/auth/tokens request. NOTE: the vendor feels that the benefit to changing this might be too small relative to the performance degradation.
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Analysis
by VulDB Data Team • 08/05/2024
The vulnerability identified as CVE-2018-20170 affects OpenStack Keystone versions through 14.0.1 and represents a user enumeration flaw that exposes sensitive information through timing discrepancies in authentication responses. This issue stems from the fact that invalid usernames receive significantly faster responses compared to valid usernames when processing POST requests to the /v3/auth/tokens endpoint. The timing difference creates a side-channel attack vector that allows malicious actors to determine the existence of valid user accounts within the system.
From a technical perspective, this vulnerability operates on the principle of timing attacks where the differential response times between valid and invalid authentication attempts can be measured and analyzed. The flaw exists in the authentication processing logic where the system performs different computational paths for valid versus invalid usernames, resulting in measurable time differences that can be exploited by attackers. This type of vulnerability aligns with CWE-203, which specifically addresses "Information Dis clo sure via Timing Discrepancies" and represents a classic example of how seemingly minor implementation details can create significant security weaknesses.
The operational impact of this vulnerability extends beyond simple user enumeration, as it provides attackers with a method to map valid user accounts within the OpenStack environment. This information can then be leveraged for subsequent attacks including brute force attempts, credential stuffing, or social engineering campaigns. The vulnerability particularly affects cloud environments where multiple users and services depend on Keystone for authentication, potentially compromising the entire cloud infrastructure. Security professionals should note that this vulnerability can be particularly dangerous in multi-tenant environments where the enumeration of valid users could reveal the presence of other organizations' accounts within the same system.
The vendor's response regarding performance degradation highlights a common challenge in security implementation where defensive measures might introduce performance overhead that could impact system usability. However, this trade-off is generally considered acceptable given the security implications of user enumeration vulnerabilities. Organizations should consider implementing consistent response times for all authentication attempts regardless of validity to prevent timing-based information disclosure. The mitigation strategy involves ensuring that all authentication requests take approximately equal time to process, which can be achieved through techniques such as adding artificial delays or implementing constant-time comparison algorithms. This approach aligns with the broader ATT&CK framework's consideration of credential access techniques and demonstrates the importance of defensive programming practices in authentication systems. The vulnerability underscores the need for security-conscious development practices and regular security assessments to identify and address timing discrepancies that could create unintended information disclosure channels.