CVE-2016-9955 in SimpleSAMLphp
Summary
by MITRE
The SimpleSAML_XML_Validator class constructor in SimpleSAMLphp before 1.14.11 might allow remote attackers to spoof signatures on SAML 1 responses or possibly cause a denial of service (memory consumption) by leveraging improper conversion of return values to boolean.
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Analysis
by VulDB Data Team • 08/15/2020
The vulnerability identified as CVE-2016-9955 affects SimpleSAMLphp versions prior to 1.14.11, specifically within the SimpleSAML_XML_Validator class constructor. This flaw represents a critical security weakness that could enable remote attackers to manipulate SAML 1.1 response signatures, potentially leading to authentication bypasses or unauthorized access to protected resources. The vulnerability stems from improper handling of return values during XML validation processes, creating a pathway for attackers to exploit the system's signature verification mechanisms.
The technical implementation of this vulnerability lies in the constructor's handling of boolean conversion operations within the XML validation logic. When SimpleSAMLphp processes SAML responses, it relies on XML validation to ensure message integrity and authenticity. The flaw occurs when the validator class converts certain return values from XML parsing functions to boolean representations without proper validation of the underlying data types. This improper conversion can result in false positive signature validations, allowing attackers to craft malicious SAML responses that appear legitimate to the validation system. The vulnerability specifically impacts SAML 1.1 responses where signature verification is critical for maintaining trust between identity providers and service providers.
The operational impact of CVE-2016-9955 extends beyond simple signature spoofing to include potential denial of service conditions. Attackers can exploit the flawed validation logic to consume excessive memory resources through malformed XML structures, leading to resource exhaustion and system instability. This dual nature of the vulnerability makes it particularly dangerous as it can be leveraged for both authentication bypass attacks and system disruption. The memory consumption aspect aligns with common attack patterns found in software vulnerability classifications, particularly those categorized under CWE-400 (Uncontrolled Resource Consumption) and CWE-295 (Improper Certificate Validation). The vulnerability affects the core authentication infrastructure of systems relying on SimpleSAMLphp for SAML integration, potentially compromising entire identity federation ecosystems.
Organizations using affected versions of SimpleSAMLphp should immediately implement mitigations including upgrading to version 1.14.11 or later, which contains the necessary patches to address the boolean conversion issues. Additionally, security teams should monitor for unusual memory consumption patterns and implement additional validation layers to detect malformed SAML responses. The vulnerability demonstrates the critical importance of proper input validation and return value handling in security-sensitive code, particularly when dealing with cryptographic operations and signature verification. Organizations should also consider implementing network-level protections such as intrusion detection systems that can identify and block suspicious SAML traffic patterns, aligning with ATT&CK technique T1566 (Phishing) and T1499 (Endpoint Denial of Service) to protect against exploitation attempts.