CVE-2020-10185 in Validation Server
Summary
by MITRE
The sync endpoint in YubiKey Validation Server before 2.40 allows remote attackers to replay an OTP. NOTE: this issue is potentially relevant to persons outside Yubico who operate a self-hosted OTP validation service with a non-default configuration such as an open sync pool; the issue does NOT affect YubiCloud.
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Analysis
by VulDB Data Team • 04/09/2024
The vulnerability identified as CVE-2020-10185 resides within the sync endpoint of YubiKey Validation Server versions prior to 2.40, presenting a significant security risk for organizations operating self-hosted OTP validation services. This flaw specifically enables remote attackers to perform OTP replay attacks, compromising the fundamental security guarantees that one-time passwords are designed to provide. The vulnerability is particularly concerning because it affects deployments where organizations have configured non-default settings such as open sync pools, which are common in enterprise environments that maintain their own validation infrastructure rather than relying on cloud-based services.
The technical implementation of this vulnerability stems from inadequate session management and validation controls within the sync endpoint functionality. When the YubiKey Validation Server processes synchronization requests, it fails to properly validate or track the uniqueness of OTP tokens being submitted. This allows attackers to capture a valid OTP from a legitimate user session and replay it against the validation server within a certain time window, effectively bypassing the one-time nature of these security tokens. The flaw operates at the protocol level where synchronization mechanisms are designed to maintain consistency across distributed validation servers, but the implementation lacks proper cryptographic validation of token freshness and uniqueness.
From an operational impact perspective, this vulnerability undermines the core security model of OTP-based authentication systems, potentially allowing unauthorized access to protected resources. Attackers can exploit this weakness to gain access to systems, applications, or services that rely on YubiKey validation for authentication purposes. The risk is amplified in environments where the sync pool is configured to be publicly accessible, as this creates an attack surface that can be leveraged without requiring prior authentication or privileged access. Organizations using self-hosted validation servers with non-default configurations face the highest risk, as these deployments typically handle sensitive authentication data and may not have the same level of security monitoring as managed cloud services.
The vulnerability aligns with CWE-319 (CWE-319: Cleartext Transmission of Sensitive Information) and CWE-347 (CWE-347: Improper Verification of Cryptographic Signature) as it involves the insecure handling of authentication tokens and potentially the transmission of sensitive validation data without proper verification mechanisms. From an ATT&CK framework perspective, this vulnerability maps to T1110 (Brute Force) and T1566 (Phishing) as attackers can leverage replay attacks to bypass authentication controls, and potentially T1078 (Valid Accounts) if they can maintain access through repeated successful authentications. Organizations should immediately update to YubiKey Validation Server version 2.40 or later, which includes proper session validation and replay protection mechanisms. Additionally, security teams should review their sync pool configurations to ensure they are not exposing unnecessary attack surfaces and implement proper monitoring for unusual synchronization patterns that might indicate replay attacks. Network segmentation and access controls should be strengthened around validation server endpoints to limit exposure to unauthorized users.