CVE-2016-10149 in PySAML2
Summary
by MITRE
XML External Entity (XXE) vulnerability in PySAML2 4.4.0 and earlier allows remote attackers to read arbitrary files via a crafted SAMPL XML request or response.
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Analysis
by VulDB Data Team • 11/15/2022
The CVE-2016-10149 vulnerability represents a critical XML External Entity processing flaw in the PySAML2 library version 4.4.0 and earlier. This vulnerability exists within the Security Assertion Markup Language implementation that handles SAML authentication protocols, making it particularly dangerous in identity and access management systems. The flaw arises from insufficient input validation when processing XML documents containing external entity references, allowing malicious actors to exploit the library's XML parser behavior. The vulnerability specifically affects systems that utilize PySAML2 for SAML request and response handling, creating a potential attack surface for remote code execution or sensitive data exfiltration.
This XXE vulnerability operates by leveraging the XML parser's capability to resolve external entity references during document processing. When a crafted SAML XML message contains malicious external entity declarations, the parser will attempt to resolve these references, potentially allowing attackers to access local files on the server hosting the vulnerable application. The attack vector specifically targets the processing of SAMPL XML requests and responses, where the library fails to properly sanitize or disable external entity resolution. The vulnerability falls under CWE-611, which classifies insecure XML processing, and represents a classic XXE exploitation scenario where remote attackers can leverage the parser's behavior to read arbitrary files from the target system's filesystem.
The operational impact of this vulnerability extends beyond simple file reading capabilities, as it can potentially lead to full system compromise when combined with other attack techniques. Attackers can use this vulnerability to access sensitive configuration files, database credentials, or application source code that may be stored locally on systems processing SAML requests. The vulnerability is particularly concerning in enterprise environments where SAML-based single sign-on implementations are common, as it could allow attackers to escalate privileges or gain unauthorized access to protected resources. This flaw can also be leveraged to perform server-side request forgery attacks, where the vulnerable system may be tricked into making unauthorized requests to internal services. The attack can be executed remotely without requiring authentication, making it especially dangerous for systems that are exposed to untrusted networks or public internet access.
Organizations should immediately upgrade to PySAML2 version 4.4.1 or later, which contains the necessary patches to disable external entity processing in XML parsers. Security teams should also implement network segmentation and access controls to limit exposure of systems that process SAML requests, while monitoring for suspicious XML processing activities. Additional mitigations include configuring XML parsers to disable external entity resolution entirely, implementing proper input validation for all XML content, and conducting comprehensive security testing of SAML implementations. The vulnerability aligns with ATT&CK technique T1059.007 for XML external entity processing, and organizations should consider implementing defensive measures such as web application firewalls that can detect and block malicious XML content. Regular security assessments of identity and access management systems are essential to identify and remediate similar vulnerabilities in other components of the authentication infrastructure.