CVE-2014-4616 in Python
Summary
by MITRE
Array index error in the scanstring function in the _json module in Python 2.7 through 3.5 and simplejson before 2.6.1 allows context-dependent attackers to read arbitrary process memory via a negative index value in the idx argument to the raw_decode function.
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Analysis
by VulDB Data Team • 08/04/2021
The vulnerability identified as CVE-2014-4616 represents a critical array index error within Python's JSON parsing implementation that affects a wide range of Python versions from 2.7 through 3.5 and simplejson versions prior to 2.6.1. This flaw exists in the scanstring function of the _json module, which is responsible for parsing JSON strings and converting them into Python data structures. The vulnerability manifests when the raw_decode function receives a negative index value through the idx argument, creating a scenario where the application processes memory locations that should remain inaccessible or unprocessed.
The technical implementation of this vulnerability stems from inadequate input validation within the JSON parsing logic. When a negative index value is passed to the scanstring function, the parsing routine fails to properly validate the boundary conditions of array access, leading to unauthorized memory access patterns. This type of flaw falls under the CWE-129 weakness category, specifically addressing insufficient validation of array indices, which is a common vector for memory corruption vulnerabilities. The vulnerability operates at the boundary between safe and unsafe memory operations, where the negative index parameter causes the parsing engine to reference memory locations that may contain sensitive data or code segments from the process heap.
The operational impact of CVE-2014-4616 extends beyond simple information disclosure to potentially enable more sophisticated attacks. Context-dependent attackers can leverage this vulnerability to read arbitrary process memory, which may contain sensitive information such as authentication tokens, cryptographic keys, or application state data. The attack vector requires that the vulnerable application processes JSON data containing maliciously crafted negative index values, typically through user input or network communication channels. This vulnerability aligns with ATT&CK technique T1059.001 for command and scripting interpreter, as attackers may use this memory disclosure to gain insights into application behavior or to facilitate further exploitation. The vulnerability can be particularly dangerous in web applications, API services, or any system that processes untrusted JSON input from external sources.
Mitigation strategies for this vulnerability require immediate patching of affected Python installations and simplejson libraries to versions that properly validate index parameters before memory access operations. Organizations should implement input validation measures that sanitize JSON data at the application boundary, rejecting any negative index values or malformed parameters before they reach the JSON parsing engine. Additionally, system administrators should consider deploying runtime protections such as address space layout randomization and stack canaries to reduce the effectiveness of potential exploitation attempts. The vulnerability demonstrates the critical importance of proper input validation in security-critical code paths, particularly in parsing libraries that handle untrusted data from external sources, and highlights the necessity of comprehensive testing for boundary condition handling in language implementations that process structured data formats.