CVE-2012-2135 in Python
Summary
by MITRE • 01/25/2023
The utf-16 decoder in Python 3.1 through 3.3 does not update the aligned_end variable after calling the unicode_decode_call_errorhandler function, which allows remote attackers to obtain sensitive information (process memory) or cause a denial of service (memory corruption and crash) via unspecified vectors.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 01/25/2023
The vulnerability described in CVE-2012-2135 represents a critical flaw in Python's Unicode handling mechanism that affects versions 3.1 through 3.3. This issue resides within the UTF-16 decoder implementation where a variable named aligned_end fails to be properly updated following calls to the unicode_decode_call_errorhandler function. The flaw stems from inadequate state management during error handling procedures, creating a scenario where the decoder's internal state becomes inconsistent with the actual data processing flow. This misalignment in state tracking creates opportunities for attackers to exploit the decoder's behavior in ways that were not anticipated during the original design phase.
The technical nature of this vulnerability manifests through improper variable management within Python's internal Unicode processing routines. When the unicode_decode_call_errorhandler function is invoked during UTF-16 decoding operations, it processes error conditions but does not properly synchronize the aligned_end variable with the current decoding state. This variable serves as a critical boundary marker that determines how much of the input data has been successfully processed and where the decoder should continue its operations. The failure to update this variable creates a condition where subsequent decoding operations may reference stale or incorrect memory addresses, leading to unpredictable behavior.
The operational impact of this vulnerability extends across multiple attack vectors that can result in either information disclosure or system instability. Remote attackers can potentially extract sensitive process memory contents by leveraging the improper state handling, as the mismanaged aligned_end variable may expose memory locations that should remain protected. Additionally, the vulnerability can trigger memory corruption conditions that lead to application crashes or even system-wide instability. The memory corruption aspect of this flaw aligns with common attack patterns documented in the attack framework, where improper state management leads to exploitable conditions that can be amplified through carefully crafted input data.
This vulnerability demonstrates characteristics consistent with CWE-665 Improper Initialization, where the failure to properly initialize or update critical state variables creates exploitable conditions. The flaw also relates to CWE-125 Out-of-bounds Read conditions that can occur when memory addresses are incorrectly calculated or referenced due to improper state tracking. From an attack perspective, this vulnerability could be classified under ATT&CK technique T1059 Command and Scripting Interpreter where attackers might leverage the memory corruption to execute arbitrary code or access sensitive information. The vulnerability represents a classic example of how subtle state management errors in low-level system components can create significant security implications.
The recommended mitigation strategies for CVE-2012-2135 involve immediate upgrades to Python versions 3.4 or later where this vulnerability has been properly addressed through corrected state management in the UTF-16 decoder. Organizations should also implement input validation measures to limit the exposure of vulnerable applications to malformed Unicode data, particularly when processing untrusted input from network sources. Additionally, monitoring systems should be configured to detect unusual memory access patterns or application crashes that might indicate exploitation attempts. The fix implemented in later Python versions demonstrates proper handling of error conditions and ensures that all internal state variables are appropriately synchronized following error handler invocations, preventing the state inconsistencies that led to this vulnerability.