CVE-2008-6547 in FormEncode
Summary
by MITRE
schema.py in FormEncode for Python (python-formencode) 1.0 does not apply the chained_validators feature, which allows attackers to bypass intended access restrictions via unknown vectors.
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Analysis
by VulDB Data Team • 04/21/2019
The vulnerability identified as CVE-2008-6547 resides within the FormEncode library for Python, specifically in the schema.py component of version 1.0. This issue represents a critical security flaw that undermines the intended validation mechanisms within the framework. The vulnerability manifests when the chained_validators feature fails to be properly applied, creating a scenario where attackers can circumvent access controls that should otherwise be enforced by the validation schema. The affected version of FormEncode was widely used in web applications that relied on Python for server-side processing, making this vulnerability particularly concerning for organizations deploying such systems.
The technical flaw stems from the improper implementation of chained validation logic within the schema processing module. When developers configure validation rules using chained_validators, they expect these rules to be executed in sequence and to collectively enforce access restrictions. However, in the vulnerable version, the schema.py file fails to properly invoke these chained validators, allowing malicious input to bypass validation checks that should have rejected it. This behavior creates a path for attackers to submit crafted data that would normally be rejected by the validation system, potentially leading to unauthorized access or data manipulation. The vulnerability operates through unknown vectors, indicating that the bypass mechanism may involve subtle interactions between different validation components or unexpected processing flows within the library.
The operational impact of this vulnerability extends beyond simple validation bypass, as it fundamentally compromises the security posture of applications relying on FormEncode for input validation. Attackers could exploit this weakness to submit malformed data that passes through validation checks, potentially leading to injection attacks, data corruption, or unauthorized access to restricted resources. Applications using FormEncode for user input processing, form validation, or API request handling would be particularly vulnerable since the flaw affects the core validation logic that protects against malicious inputs. The chained_validators feature is designed to create complex validation rules that must all pass before data is considered valid, but this protection is entirely circumvented when the feature fails to execute properly. This vulnerability directly relates to CWE-284, which addresses improper access control, and could be leveraged to achieve privilege escalation or data breach scenarios.
Organizations should prioritize immediate remediation by upgrading to a patched version of FormEncode that properly implements the chained_validators feature. The mitigation strategy should include comprehensive testing of all input validation flows to ensure that chained validators are functioning correctly. Security teams should also conduct thorough audits of applications using FormEncode to identify any potential exploitation vectors that might have been previously overlooked. Additionally, implementing additional layers of validation and monitoring can help detect anomalous input patterns that might indicate exploitation attempts. The vulnerability highlights the importance of proper validation chain implementation and demonstrates how a single flaw in a validation library can compromise entire application security models, making it essential for developers to understand and properly test their validation configurations. This issue represents a fundamental failure in the security architecture of affected systems and requires immediate attention to prevent potential exploitation.