CVE-2008-1721 in Python
Summary
by MITRE
Integer signedness error in the zlib extension module in Python 2.5.2 and earlier allows remote attackers to execute arbitrary code via a negative signed integer, which triggers insufficient memory allocation and a buffer overflow.
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Analysis
by VulDB Data Team • 12/27/2025
The vulnerability identified as CVE-2008-1721 represents a critical integer signedness error within the zlib extension module of Python versions 2.5.2 and earlier. This flaw stems from improper handling of signed integer values during decompression operations, creating a pathway for remote code execution through carefully crafted malicious input. The issue manifests when the decompression process encounters a negative signed integer value that is subsequently interpreted as an unsigned value, leading to miscalculations in memory allocation decisions.
The technical root cause of this vulnerability aligns with CWE-195, which addresses signed to unsigned conversion errors, and specifically demonstrates how improper integer handling can lead to buffer overflows. When the zlib module processes compressed data containing a negative signed integer, the system fails to properly validate the integer bounds before using it for memory allocation calculations. This oversight results in insufficient memory being allocated for the decompression buffer, creating a scenario where subsequent data writes exceed the allocated memory boundaries and trigger a buffer overflow condition.
The operational impact of CVE-2008-1721 extends beyond simple memory corruption, as it provides attackers with a reliable method for executing arbitrary code on affected systems. Attackers can craft malicious compressed data streams that, when processed by vulnerable Python applications, will cause the application to allocate insufficient memory and subsequently overflow the buffer. This vulnerability affects any Python application that utilizes the zlib module for decompressing data from untrusted sources, making it particularly dangerous in web applications, file processing systems, and network services that handle compressed data inputs.
The exploitability of this vulnerability is enhanced by the fact that it operates at the decompression layer, where input validation may be minimal or absent. Systems running Python 2.5.2 or earlier versions are particularly susceptible, as they lack the integer overflow protections and input sanitization measures that were later implemented in subsequent releases. This vulnerability directly maps to attack techniques described in the ATT&CK framework under the T1203 category, specifically targeting the exploitation of input validation weaknesses to achieve code execution.
Mitigation strategies for CVE-2008-1721 primarily involve upgrading to Python versions 2.5.3 or later, where the integer signedness error has been corrected through proper input validation and memory allocation checks. Organizations should also implement input sanitization measures at application layers that process compressed data, including validating data integrity before decompression operations and monitoring for anomalous integer values. Additionally, network segmentation and application firewalls can help limit the attack surface by restricting access to vulnerable Python applications and preventing unauthorized data injection attempts that could exploit this vulnerability.