CVE-2018-15801 in Spring Security
Summary
by MITRE
Spring Security versions 5.1.x prior to 5.1.2 contain an authorization bypass vulnerability during JWT issuer validation. In order to be impacted, the same private key for an honest issuer and a malicious user must be used when signing JWTs. In that case, a malicious user could fashion signed JWTs with the malicious issuer URL that may be granted for the honest issuer.
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Analysis
by VulDB Data Team • 06/19/2023
This vulnerability exists within Spring Security's implementation of JSON Web Token (JWT) validation mechanisms, specifically affecting versions 5.1.x prior to 5.1.2. The flaw represents a critical authorization bypass that exploits the improper handling of issuer validation during JWT processing. The vulnerability stems from the system's failure to properly validate the issuer claim when the same private key is used for both legitimate and malicious JWT signing operations. This weakness creates a scenario where an attacker can manipulate JWT tokens to appear as if they originate from a trusted issuer, despite being generated by an unauthorized party.
The technical implementation flaw occurs during the JWT issuer validation process where Spring Security does not adequately verify that the issuer URL in the token matches the expected issuer configuration. When both legitimate and malicious parties share the same private key for signing JWTs, the system accepts tokens signed with that key regardless of the issuer claim contained within the token. This represents a direct violation of the principle of least privilege and certificate path validation, where the system should ensure that tokens originate from authorized sources. The vulnerability is particularly dangerous because it operates at the authentication and authorization layer, potentially allowing attackers to escalate privileges or gain unauthorized access to protected resources. This flaw aligns with CWE-287 which addresses improper authentication and CWE-345 which covers insufficient verification of data integrity.
The operational impact of this vulnerability is significant as it allows attackers to bypass authorization controls without requiring additional credentials or exploiting other system weaknesses. An attacker who gains access to a shared private key can forge JWT tokens that appear legitimate to the Spring Security system, potentially granting them access to resources that should only be available to authorized users. This could lead to data breaches, unauthorized system access, privilege escalation, and other security incidents. The vulnerability affects systems that rely on JWT-based authentication and authorization, particularly those using Spring Security 5.1.x versions before the patch was released. The attack vector requires the attacker to possess the private key used for signing, but does not require additional system compromise or complex exploitation techniques. This makes the vulnerability particularly concerning as it can be exploited by insiders or attackers who have obtained legitimate credentials or keys.
The recommended mitigation strategy involves upgrading to Spring Security 5.1.2 or later versions where the issuer validation has been properly implemented and hardened. Organizations should also implement proper key management practices, ensuring that private keys are not shared between legitimate and malicious parties. Additional mitigations include implementing proper key rotation procedures, using separate signing keys for different issuers, and adding additional validation layers beyond the basic JWT issuer claim. Security teams should conduct thorough audits of their JWT implementation to identify any systems that may be affected by this vulnerability and implement proper monitoring to detect suspicious authentication patterns. This vulnerability highlights the importance of proper cryptographic implementation and the need for robust validation mechanisms in authentication systems. The fix addresses the core issue by strengthening the JWT issuer validation logic to ensure that tokens cannot be forged to appear as legitimate from unauthorized sources, thereby maintaining the integrity of the authorization process. Organizations should also consider implementing additional security controls such as token binding, time-based validation, and enhanced logging to provide better detection and prevention capabilities.