CVE-2019-11324 in urllib3
Summary
by MITRE
The urllib3 library before 1.24.2 for Python mishandles certain cases where the desired set of CA certificates is different from the OS store of CA certificates, which results in SSL connections succeeding in situations where a verification failure is the correct outcome. This is related to use of the ssl_context, ca_certs, or ca_certs_dir argument.
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Analysis
by VulDB Data Team • 10/13/2024
The vulnerability identified as CVE-2019-11324 affects the urllib3 library in Python versions prior to 1.24.2, representing a critical security flaw in SSL/TLS certificate verification mechanisms. This issue specifically targets how the library handles cases where applications need to verify SSL connections against a custom set of Certificate Authority certificates rather than relying on the operating system's default certificate store. The flaw arises from improper handling of the ssl_context, ca_certs, or ca_certs_dir arguments during SSL connection establishment, creating a scenario where security checks can be bypassed without proper validation.
The technical implementation of this vulnerability stems from the library's certificate verification logic failing to properly enforce certificate authority validation when custom certificate paths are specified. When developers configure urllib3 to use specific CA certificate files or directories through the mentioned arguments, the library does not correctly validate that the certificates provided actually correspond to trusted authorities. This creates a false sense of security where connections appear successful even when they should have been rejected due to certificate verification failures. The vulnerability operates at the transport layer security level and can be categorized under CWE-295 which addresses improper certificate validation.
From an operational perspective, this vulnerability poses significant risks to applications that rely on urllib3 for secure HTTP communications. Attackers could potentially exploit this flaw by crafting malicious certificates that would be accepted by the library when they should be rejected, leading to man-in-the-middle attacks, data interception, and unauthorized access to sensitive information. The impact extends beyond simple network communication as it undermines the fundamental security guarantees that SSL/TLS protocols are designed to provide. Organizations using affected versions of urllib3 in production environments face potential exposure to certificate pinning bypasses and credential theft scenarios.
The mitigation strategy involves upgrading to urllib3 version 1.24.2 or later, which contains the necessary fixes to properly validate certificate authorities when custom certificate paths are specified. Security teams should also implement comprehensive testing procedures to verify that SSL certificate validation works correctly in their specific deployment environments, particularly when using custom CA certificate stores. Additional defensive measures include monitoring network traffic for anomalous SSL connection patterns, implementing certificate transparency monitoring, and ensuring that all applications using urllib3 are regularly updated as part of standard security maintenance procedures. This vulnerability aligns with ATT&CK technique T1566 which covers credential harvesting through phishing and network infiltration methods, as compromised SSL connections can facilitate unauthorized access to sensitive data and systems.