CVE-2019-9641 in PHP
Summary
by MITRE
An issue was discovered in the EXIF component in PHP before 7.1.27, 7.2.x before 7.2.16, and 7.3.x before 7.3.3. There is an uninitialized read in exif_process_IFD_in_TIFF.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 07/31/2023
The vulnerability identified as CVE-2019-9641 represents a critical uninitialized read flaw within PHP's EXIF component that affects multiple versions of the PHP runtime environment. This issue specifically manifests in the exif_process_IFD_in_TIFF function, which is responsible for processing image file directories within TIFF formatted files. The vulnerability arises when PHP processes EXIF data from image files, particularly those containing malformed or crafted TIFF metadata structures that trigger the uninitialized memory access pattern.
The technical nature of this vulnerability falls under CWE-457 which defines "Use of Uninitialized Variable" as a fundamental flaw where a program attempts to use a variable that has not been initialized. In this case, the uninitialized read occurs during the parsing of IFD (Image File Directory) structures within TIFF files, where the EXIF component accesses memory locations that have not been properly initialized with valid data. This flaw can be exploited through specially crafted image files that contain malformed EXIF metadata, causing the PHP application to read from uninitialized memory regions that may contain sensitive data or previously allocated values from other program components.
The operational impact of CVE-2019-9641 extends beyond simple application instability, as it presents potential security risks that could be leveraged by attackers to extract sensitive information from memory or potentially achieve remote code execution depending on the execution environment. When PHP applications process user-uploaded images containing malicious EXIF data, the uninitialized read can lead to information disclosure vulnerabilities where attackers might recover previously used memory values that could contain passwords, session tokens, or other sensitive data. This vulnerability is particularly concerning in web applications where PHP processes user-generated content, as it can be exploited through file upload functionality without requiring authentication.
The attack surface for this vulnerability is significant within PHP-based web applications that handle image file uploads and processing, especially those that utilize the GD library or other image manipulation components that depend on PHP's EXIF functionality. Attackers can craft TIFF image files with malformed IFD structures that trigger the uninitialized read condition when PHP attempts to parse the EXIF metadata during image processing operations. This vulnerability aligns with ATT&CK technique T1203 which describes "Exploitation for Client Execution" and can be classified under the broader category of information disclosure attacks that leverage memory corruption vulnerabilities.
Mitigation strategies for CVE-2019-9641 primarily involve upgrading PHP installations to versions that contain the fix, specifically PHP 7.1.27, 7.2.16, or 7.3.3 and later. Organizations should implement comprehensive patch management procedures to ensure all affected PHP installations are updated promptly. Additionally, applications should validate and sanitize all image file uploads through proper file type checking, content verification, and consider implementing stricter file processing controls that limit the exposure of potentially malicious EXIF data. Input validation and proper error handling should be implemented to prevent the processing of malformed image files, while monitoring systems should be deployed to detect potential exploitation attempts through unusual file processing patterns or memory access anomalies.