CVE-2020-5233 in OAuth2 Proxy
Summary
by MITRE
OAuth2 Proxy before 5.0 has an open redirect vulnerability. Authentication tokens could be silently harvested by an attacker. This has been patched in version 5.0.
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Analysis
by VulDB Data Team • 03/27/2024
The OAuth2 Proxy vulnerability identified as CVE-2020-5233 represents a critical security flaw in versions prior to 5.0 that enables attackers to exploit open redirect mechanisms within the authentication flow. This vulnerability specifically targets the application's handling of redirect URLs during the OAuth2 authentication process, creating a pathway for malicious actors to manipulate the redirect behavior and potentially capture authentication tokens. The flaw exists in the way the proxy validates and processes redirect parameters, allowing unauthorized redirection to attacker-controlled domains without proper validation checks.
The technical implementation of this vulnerability stems from insufficient input sanitization and validation of redirect URLs within the OAuth2 authentication flow. When users attempt to authenticate through the proxy, the system accepts redirect parameters directly from the authentication provider without adequate verification of the target domain. This creates an environment where an attacker can craft malicious redirect URLs that appear legitimate to the user but actually direct them to attacker-controlled servers. The vulnerability is classified under CWE-601 as an open redirect vulnerability, which allows web applications to redirect users to external domains without proper validation, making it a prime target for phishing attacks and credential harvesting.
The operational impact of this vulnerability extends beyond simple token harvesting, as it enables sophisticated attack vectors that can lead to complete session compromise and unauthorized access to protected resources. Attackers can leverage this vulnerability to create convincing phishing pages that mimic legitimate authentication interfaces, potentially capturing not only OAuth2 tokens but also session cookies and other sensitive authentication data. The silent harvesting aspect means users remain unaware that their authentication tokens are being collected, making this attack particularly dangerous as it operates without user detection. This vulnerability aligns with ATT&CK technique T1566.002 which covers phishing with malicious attachments and links, specifically targeting the authentication and credential access phases of the attack lifecycle.
Mitigation strategies for CVE-2020-5233 require immediate implementation of the patched version 5.0 or equivalent security measures that enforce strict redirect URL validation. Organizations should ensure that all redirect parameters are validated against a predefined whitelist of trusted domains, implementing proper URL sanitization and canonicalization checks. The fix typically involves modifying the application's redirect handling logic to verify that redirect targets are within the expected domain boundaries and rejecting any redirects that point to external or untrusted locations. Additionally, security teams should implement monitoring for suspicious redirect patterns and consider implementing additional authentication layers such as multi-factor authentication to reduce the impact of potential token compromise. Network-level protections including web application firewalls and strict ingress/egress policies can provide additional defense-in-depth measures against exploitation attempts.