CVE-2016-5636 in macOS
Summary
by MITRE
Integer overflow in the get_data function in zipimport.c in CPython (aka Python) before 2.7.12, 3.x before 3.4.5, and 3.5.x before 3.5.2 allows remote attackers to have unspecified impact via a negative data size value, which triggers a heap-based buffer overflow.
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Analysis
by VulDB Data Team • 11/20/2022
The vulnerability described in CVE-2016-5636 represents a critical integer overflow flaw within the zipimport module of CPython, affecting multiple versions of the Python interpreter. This vulnerability resides in the get_data function within zipimport.c, which is responsible for processing zip archives containing python modules. The flaw occurs when the function encounters a negative data size value during the extraction process, creating a scenario where integer arithmetic produces unexpected results that can lead to memory corruption. The vulnerability impacts Python versions prior to 2.7.12, 3.4.5, and 3.5.2, making it a widespread issue affecting a significant portion of Python installations in use at the time of discovery.
The technical mechanism behind this vulnerability involves the improper handling of data size parameters within the zipimport module. When processing zip archives, the get_data function performs arithmetic operations on size values that are extracted from the zip file headers. In normal operation, these values should be positive integers representing the size of data blocks. However, when a maliciously crafted zip file contains a negative value in the size field, the integer overflow occurs during the conversion process. This overflow results in a heap-based buffer overflow condition, where the application attempts to allocate memory using an incorrect size value, potentially leading to memory corruption that can be exploited by remote attackers.
The operational impact of this vulnerability extends beyond simple memory corruption, as it provides attackers with potential remote code execution capabilities through heap-based buffer overflow exploitation techniques. Attackers can craft malicious zip files with negative size values that, when processed by vulnerable Python applications, trigger the buffer overflow condition. This vulnerability is particularly concerning because zipimport is commonly used by Python applications to import modules from zip archives, making it a potential attack vector in various Python deployments including web applications, automated systems, and any environment where Python processes zip files containing external modules. The unspecified impact mentioned in the CVE description suggests that exploitation could lead to arbitrary code execution, denial of service, or information disclosure depending on the specific execution context and memory layout.
Mitigation strategies for CVE-2016-5636 primarily focus on upgrading to patched versions of CPython where the integer overflow has been addressed through proper input validation and size parameter checking. System administrators should prioritize updating Python installations to versions 2.7.12, 3.4.5, or 3.5.2 and later, which contain the necessary fixes for this vulnerability. Additional protective measures include implementing strict input validation for zip file processing, disabling zipimport functionality when possible, and using application sandboxing techniques to limit the potential impact of successful exploitation attempts. From a cybersecurity perspective, this vulnerability aligns with CWE-190, which describes integer overflow conditions, and represents a classic example of how seemingly benign input validation failures can create serious security risks. The vulnerability also maps to ATT&CK technique T1059.006, which covers execution through scripting, as exploitation typically involves crafting malicious zip files that trigger the vulnerable code path during script execution. Organizations should also consider implementing network segmentation and monitoring for suspicious zip file processing activities, particularly in environments where Python applications handle untrusted input from external sources.