CVE-2020-5407 in Spring Security
Summary
by MITRE
Spring Security versions 5.2.x prior to 5.2.4 and 5.3.x prior to 5.3.2 contain a signature wrapping vulnerability during SAML response validation. When using the spring-security-saml2-service-provider component, a malicious user can carefully modify an otherwise valid SAML response and append an arbitrary assertion that Spring Security will accept as valid.
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Analysis
by VulDB Data Team • 10/18/2020
The vulnerability identified as CVE-2020-5407 represents a critical signature wrapping flaw within Spring Security's SAML response validation mechanism. This weakness affects versions 5.2.x prior to 5.2.4 and 5.3.x prior to 5.3.2 of the spring-security-saml2-service-provider component, creating a significant security risk for organizations relying on SAML-based single sign-on implementations. The flaw stems from insufficient validation of SAML response signatures, allowing attackers to manipulate authenticated responses without detection.
The technical nature of this vulnerability involves the improper handling of SAML response signatures during validation processes. When a SAML response is processed by Spring Security's SAML2 service provider, the system should verify that all assertions within the response are properly signed and that the signature covers the complete response content. However, the vulnerability allows malicious actors to append arbitrary assertions to valid SAML responses while maintaining the original signature's validity. This occurs because the signature verification mechanism fails to adequately validate the complete assertion structure and content, enabling attackers to inject unauthorized assertions that will be accepted as legitimate by the security system.
From an operational impact perspective, this vulnerability creates a severe risk for identity and access management systems that rely on SAML authentication. Attackers can exploit this weakness to gain unauthorized access to protected resources by crafting malicious SAML responses that contain additional assertions granting privileges or access rights. The vulnerability essentially allows for privilege escalation attacks where attackers can append assertions that provide them with elevated permissions or access to systems they should not be able to reach. This could result in data breaches, unauthorized system access, and complete compromise of identity federation systems that depend on Spring Security's SAML implementation.
Organizations implementing Spring Security SAML2 service provider components should immediately upgrade to versions 5.2.4 or 5.3.2 and later to remediate this vulnerability. The fix addresses the signature validation logic to properly verify the complete SAML response structure and ensure that any modifications to assertions invalidate the response signature. Security teams should also implement additional monitoring for suspicious authentication patterns and consider deploying network-based detection mechanisms to identify potential exploitation attempts. This vulnerability aligns with CWE-347, which addresses improper verification of cryptographic signatures, and maps to ATT&CK technique T1550.001 for valid accounts and T1550.002 for use of stolen credentials, as it enables attackers to effectively bypass authentication controls through signature manipulation rather than direct credential theft.
The broader implications extend beyond immediate exploitation as this vulnerability demonstrates the critical importance of proper cryptographic validation in identity management systems. Organizations using Spring Security should conduct comprehensive security assessments of their SAML implementations and review all authentication flows to ensure that similar signature validation weaknesses do not exist in other components of their security infrastructure. The vulnerability highlights the need for robust security testing practices, particularly around cryptographic validation and signature handling, to prevent similar issues in other identity federation implementations that may be susceptible to similar signature wrapping attacks.