CVE-2016-10127 in PySAML2
Summary
by MITRE
PySAML2 allows remote attackers to conduct XML external entity (XXE) attacks via a crafted SAML XML request or response.
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Analysis
by VulDB Data Team • 10/24/2024
The vulnerability identified as CVE-2016-10127 resides within the PySAML2 library, a Python implementation of the SAML 2.0 standard used for authentication and authorization in single sign-on environments. This flaw represents a critical security weakness that enables remote attackers to exploit XML external entity processing mechanisms within SAML communications. The vulnerability specifically affects how the library handles XML parsing of SAML requests and responses, creating an attack surface where malicious actors can manipulate XML documents to trigger unintended behavior during processing.
The technical root cause of this vulnerability stems from insufficient input validation and XML parser configuration within the PySAML2 library. When processing SAML messages, the library fails to properly disable external entity resolution and XML schema validation, allowing attackers to craft malicious SAML documents containing XML external entity declarations. These entities can reference external resources or perform server-side request forgery attacks, potentially leading to data exfiltration, denial of service conditions, or even remote code execution depending on the target system configuration. The vulnerability aligns with CWE-611, which specifically addresses improper restriction of XML external entity reference, and represents a classic XXE attack vector that has been prevalent across numerous web applications and libraries.
The operational impact of this vulnerability extends beyond simple data exposure, as it can compromise entire authentication infrastructures that rely on SAML protocols. Attackers can leverage this weakness to access sensitive user information, perform unauthorized authentication attempts, or disrupt service availability through resource exhaustion attacks. In enterprise environments where SAML is commonly used for federated identity management, this vulnerability could enable attackers to bypass authentication mechanisms and gain unauthorized access to protected resources. The attack requires minimal privileges and can be executed against any system utilizing the vulnerable PySAML2 library, making it particularly dangerous in large-scale deployments.
Organizations should implement immediate mitigations including updating to patched versions of PySAML2 where available, configuring XML parsers to disable external entity resolution, and implementing network-level restrictions to prevent unauthorized access to SAML endpoints. Security teams should also conduct comprehensive assessments of all systems utilizing SAML authentication to identify potential exposure points and ensure proper XML processing configurations. From an ATT&CK framework perspective, this vulnerability maps to technique T1059.007 for XML external entity processing and T1566 for credential access through authentication bypass mechanisms, highlighting the multi-faceted nature of the threat. Additionally, implementing proper input sanitization, using secure XML parsing libraries, and conducting regular security testing of authentication components will help reduce the risk of exploitation in environments where SAML is deployed.