CVE-2020-27619 in Python
Summary
by MITRE • 10/22/2020
In Python 3 through 3.9.0, the Lib/test/multibytecodec_support.py CJK codec tests call eval() on content retrieved via HTTP.
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Analysis
by VulDB Data Team • 02/21/2022
The vulnerability identified as CVE-2020-27619 represents a critical security flaw in Python versions ranging from 3.0 through 3.9.0 that stems from improper handling of external content within the testing framework. This issue specifically affects the Lib/test/multibytecodec_support.py file which contains CJK codec tests designed to validate international character encoding support. The flaw occurs when these tests retrieve content over HTTP connections and subsequently execute eval() operations on the received data without proper sanitization or validation. This behavior creates a significant attack surface where malicious actors could potentially inject arbitrary code that would be executed within the context of the Python testing environment. The vulnerability falls under the category of code injection flaws and aligns with CWE-94, which describes the execution of arbitrary code or commands due to insufficient input validation. The operational impact extends beyond simple testing environments as this flaw could be exploited in scenarios where Python is used for automated testing or continuous integration pipelines that might inadvertently execute these vulnerable test modules.
The technical implementation of this vulnerability demonstrates a dangerous pattern of trust assumptions within the Python testing infrastructure. When the multibytecodec_support.py module fetches data from remote HTTP sources for testing purposes, it assumes that all retrieved content is safe and legitimate without implementing proper security measures. The use of eval() function on external data represents a classic security anti-pattern that has been documented across numerous security frameworks and standards including those referenced in the ATT&CK framework under T1059.001 for command and scripting interpreter. The vulnerability is particularly concerning because it exists within the standard library testing components rather than application code, meaning that any Python installation with these versions could potentially be compromised simply by executing tests that utilize the affected modules. Attackers could craft malicious HTTP responses containing specially crafted payloads that would be executed as Python code when the eval() function processes them. This creates a scenario where an attacker controlling a remote server could execute arbitrary code on systems running vulnerable Python versions, effectively bypassing traditional application-level security controls.
The implications of this vulnerability extend to organizations that rely on automated testing environments or continuous integration systems that may execute Python test suites without proper sandboxing or network isolation. Modern security practices emphasize the principle of least privilege and the need to avoid executing untrusted code, particularly within development and testing environments where such operations might be performed with elevated permissions. The vulnerability demonstrates the importance of secure coding practices in all code components, including testing infrastructure, as these areas often receive less security scrutiny than production code. Organizations utilizing Python versions within the affected range should consider immediate mitigation strategies including updating to patched versions, implementing network restrictions to prevent access to untrusted HTTP endpoints during testing, or modifying test configurations to disable the vulnerable test modules. The ATT&CK framework categorizes this type of vulnerability under software development security practices, specifically highlighting the need for secure handling of external inputs and avoiding dangerous functions like eval() in production code. This vulnerability serves as a reminder that even testing components within standard libraries must adhere to the same security principles as application code, as they can provide attack vectors that compromise entire systems when exploited by malicious actors.