CVE-2013-1665 in Python
Summary
by MITRE
The XML libraries for Python 3.4, 3.3, 3.2, 3.1, 2.7, and 2.6, as used in OpenStack Keystone Essex and Folsom, Django, and possibly other products allow remote attackers to read arbitrary files via an XML external entity declaration in conjunction with an entity reference, aka an XML External Entity (XXE) attack.
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Analysis
by VulDB Data Team • 05/05/2021
The vulnerability identified as CVE-2013-1665 represents a critical XML External Entity processing flaw that affects multiple versions of Python's XML libraries across various widely-used software platforms. This vulnerability specifically targets the way XML parsers handle external entity declarations and references, creating a pathway for remote attackers to exploit the system's XML processing capabilities. The flaw is particularly concerning because it affects Python versions 2.6 through 3.4, encompassing a broad range of applications including OpenStack Keystone versions Essex and Folsom, Django web framework, and numerous other products that rely on Python's XML processing libraries. The vulnerability operates by leveraging the XML parser's ability to resolve external entities, which can be manipulated to reference local files on the server system, potentially exposing sensitive data and system information to unauthorized parties.
The technical implementation of this vulnerability stems from improper input validation within XML parsing functions that fail to adequately sanitize external entity declarations. When an XML document contains a declaration of external entities, the parser processes these declarations and attempts to resolve them, creating an attack surface where malicious actors can craft XML payloads that reference arbitrary local files. This weakness is categorized under CWE-611 as "Improper Restriction of XML External Entity Reference" and aligns with the ATT&CK technique T1213.002 for "Data from Information Repositories" through XML External Entity processing. The vulnerability exists in the core XML parsing libraries where external entity resolution occurs without proper restrictions on the sources or types of entities that can be referenced, allowing attackers to construct XML documents that contain entity references pointing to system files, configuration files, or other sensitive resources accessible to the application process.
The operational impact of this vulnerability extends far beyond simple data exposure, as it can enable attackers to perform reconnaissance, extract sensitive information, and potentially escalate privileges within affected systems. In the context of OpenStack Keystone, this vulnerability could allow attackers to access authentication credentials, configuration files containing database connection strings, or other sensitive information that would normally be protected from direct file system access. The Django framework and other affected applications could see similar exposure of application configuration data, user information, or system resources that are accessible through file system paths. Attackers could leverage this vulnerability to read system files such as /etc/passwd, application configuration files, or database connection details, creating a significant risk for organizations using affected software versions. The remote nature of the attack means that exploitation does not require local system access or physical presence, making it particularly dangerous in cloud environments or multi-tenant systems where the attack surface is expanded.
Mitigation strategies for CVE-2013-1665 must address both the immediate vulnerability and establish long-term security practices to prevent similar issues. Organizations should immediately upgrade to patched versions of Python XML libraries, ensuring that all affected versions are updated to prevent exploitation. The recommended approach involves implementing strict XML parser configurations that disable external entity resolution, particularly by setting appropriate parser flags to prevent loading of external DTDs and entities. Security measures should include input validation and sanitization of all XML data received from untrusted sources, implementing proper access controls to limit file system access, and establishing monitoring for unusual file access patterns that might indicate exploitation attempts. Additionally, organizations should consider implementing network segmentation, using intrusion detection systems to monitor for XML-based attack patterns, and conducting regular security assessments of XML processing components within their applications. The remediation process should also include reviewing and updating security policies to ensure that XML processing functions are properly configured to reject external entity declarations, as specified in security standards such as the OWASP XML External Entity Prevention Cheat Sheet and industry best practices for secure coding.