CVE-2017-18924 in oauth2-server
Summary
by MITRE • 10/04/2020
** DISPUTED ** oauth2-server (aka node-oauth2-server) through 3.1.1 implements OAuth 2.0 without PKCE. It does not prevent authorization code injection. This is similar to CVE-2020-7692. NOTE: the vendor states 'As RFC7636 is an extension, I think the claim in the Readme of "RFC 6749 compliant" is valid and not misleading and I also therefore wouldn't describe this as a "vulnerability" with the library per se.'
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Analysis
by VulDB Data Team • 08/06/2024
The vulnerability identified as CVE-2017-18924 pertains to the oauth2-server library version 3.1.1 and earlier implementations that lack support for Proof Key for Code Exchange (PKCE) functionality. This represents a significant security gap in the OAuth 2.0 authorization framework where the library fails to implement the RFC 7636 standard that was specifically designed to address authorization code injection attacks. The issue arises from the absence of PKCE validation mechanisms that would normally prevent attackers from intercepting authorization codes and potentially exploiting them through various injection techniques.
The technical flaw manifests in the library's failure to enforce the PKCE extension during the authorization code flow, creating a pathway for attackers to perform authorization code injection attacks. Without PKCE, the OAuth 2.0 implementation becomes vulnerable to man-in-the-middle attacks where malicious actors can intercept authorization codes and potentially gain unauthorized access to protected resources. This vulnerability directly aligns with CWE-305 authentication bypass issues and corresponds to ATT&CK technique T1566.001 for credential access through social engineering and T1562.001 for defense evasion through protocol manipulation. The absence of PKCE validation means that the library cannot properly verify that the authorization request originated from the same client that will ultimately exchange the authorization code for an access token.
The operational impact of this vulnerability extends beyond simple authorization bypass scenarios, as it fundamentally weakens the security posture of applications relying on this library for OAuth 2.0 implementation. Attackers can exploit this weakness to perform token injection attacks, potentially gaining access to user accounts, sensitive data, and system resources that should be protected by proper authentication mechanisms. The vulnerability affects web applications and services that utilize the node-oauth2-server library for implementing OAuth 2.0 flows, particularly those handling sensitive user information or privileged access controls. Organizations deploying applications using this library face increased risk of credential compromise and unauthorized access to their protected resources, making this a critical security concern for any system requiring robust authentication and authorization controls.
Despite the vendor's assertion that the library remains compliant with RFC 6749 since PKCE is considered an extension, this position is problematic from a security perspective as it fails to address the practical implementation gaps that expose systems to real-world attacks. The recommended mitigations include upgrading to newer versions of the library that properly implement PKCE support, implementing additional security controls such as token binding, and conducting thorough security assessments of existing implementations. Organizations should also consider implementing alternative authentication mechanisms or additional layers of security validation to compensate for the missing PKCE functionality. The vulnerability serves as a reminder of the importance of implementing complete security standards rather than relying solely on compliance with base specifications, as the absence of critical extensions like PKCE can leave systems vulnerable to sophisticated attack vectors that exploit the fundamental weaknesses in the authorization flow.