CVE-2017-18207 in Python
Summary
by MITRE
The Wave_read._read_fmt_chunk function in Lib/wave.py in Python through 3.6.4 does not ensure a nonzero channel value, which allows attackers to cause a denial of service (divide-by-zero error and application crash) via a crafted wav format audio file.
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Analysis
by VulDB Data Team • 08/06/2024
The vulnerability identified as CVE-2017-18207 resides within the Python standard library's wave module, specifically in the Wave_read._read_fmt_chunk function. This flaw represents a classic input validation issue that can be exploited to trigger a denial of service condition. The vulnerability affects Python versions through 3.6.4 and stems from the failure to properly validate audio file metadata during the parsing process. When processing a specially crafted wav file, the function attempts to read the channel count from the file header without ensuring that this value is non-zero, creating a critical condition that can be leveraged by malicious actors.
The technical implementation of this vulnerability involves the wave module's handling of audio file format specifications. During the parsing of wav files, the _read_fmt_chunk function reads the format chunk header which contains essential metadata including the number of audio channels. When an attacker crafts a wav file with a zero channel value in the format header, the Python interpreter encounters a divide-by-zero error during subsequent processing operations. This occurs because the code assumes a non-zero channel count for mathematical operations and buffer calculations, leading to an arithmetic exception that crashes the application. The vulnerability demonstrates poor error handling and input validation practices that are commonly associated with CWE-369, which specifically addresses the issue of dividing by zero in software implementations.
From an operational perspective, this vulnerability presents a significant risk to applications that process user-uploaded audio files or stream audio content from untrusted sources. The denial of service impact can be severe as it allows remote attackers to crash Python applications that utilize the wave module for audio file processing. This type of vulnerability is particularly dangerous in web applications, media processing services, or any system that accepts wav file uploads without proper validation. The attack vector is straightforward - an attacker simply needs to create a malicious wav file with zero channels and upload it to a vulnerable system, causing the application to crash and potentially disrupting service availability for legitimate users.
The exploitation of this vulnerability aligns with ATT&CK technique T1499.004, which involves network denial of service attacks through application or service vulnerabilities. Organizations should implement proper input validation and sanitization measures to prevent such attacks. The recommended mitigations include upgrading to Python versions where this vulnerability has been patched, implementing strict input validation for audio file formats, and employing defensive programming practices such as checking for zero values before performing mathematical operations. Additionally, applications should be designed with proper exception handling to prevent crash conditions and maintain service availability even when processing malformed input files. The vulnerability also underscores the importance of following secure coding practices as outlined in OWASP Top Ten and other security frameworks that emphasize the need for robust input validation and error handling in all software components.