CVE-2016-6291 in macOS
Summary
by MITRE
The exif_process_IFD_in_MAKERNOTE function in ext/exif/exif.c in PHP before 5.5.38, 5.6.x before 5.6.24, and 7.x before 7.0.9 allows remote attackers to cause a denial of service (out-of-bounds array access and memory corruption), obtain sensitive information from process memory, or possibly have unspecified other impact via a crafted JPEG image.
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Analysis
by VulDB Data Team • 09/20/2022
The vulnerability identified as CVE-2016-6291 represents a critical out-of-bounds array access flaw within PHP's exif extension, specifically in the exif_process_IFD_in_MAKERNOTE function located in ext/exif/exif.c. This vulnerability affects multiple PHP versions including 5.5.x before 5.5.38, 5.6.x before 5.6.24, and 7.x before 7.0.9, making it a widespread issue across the PHP ecosystem. The flaw stems from inadequate input validation when processing JPEG images containing maliciously crafted maker notes, which are metadata sections embedded within image files that typically contain camera-specific information. When PHP attempts to parse these malformed maker notes, the function fails to properly bounds-check array accesses, leading to memory corruption vulnerabilities that can be exploited remotely.
The technical nature of this vulnerability aligns with CWE-129, which describes improper validation of array index values, and specifically manifests as an out-of-bounds read condition that can result in memory corruption. Attackers can craft specially designed JPEG images with malformed maker note structures that, when processed by PHP's exif extension, trigger the vulnerable code path. This allows remote attackers to manipulate memory access patterns that exceed the allocated array boundaries, potentially causing the application to read or write to unauthorized memory locations. The impact extends beyond simple denial of service to include information disclosure, where sensitive data from process memory may be exposed to attackers, and in some cases, could potentially enable further exploitation techniques.
From an operational perspective, this vulnerability poses significant risks to web applications that process user-uploaded images, as it can be leveraged to cause denial of service conditions that disrupt legitimate service operations. The vulnerability is particularly dangerous in environments where PHP applications handle image uploads from untrusted sources, such as social media platforms, content management systems, or any application that processes user-generated media content. The potential for information disclosure makes this vulnerability especially concerning for applications running in environments where sensitive data might be present in memory, as attackers could extract database connection strings, session tokens, or other confidential information. This vulnerability can be exploited through the standard web application attack surface, requiring no special privileges or access beyond the ability to upload or provide a malicious JPEG file to a vulnerable PHP application.
The mitigation strategies for CVE-2016-6291 primarily involve upgrading to patched versions of PHP, specifically PHP 5.5.38, 5.6.24, or 7.0.9, which contain the necessary code fixes to properly validate array bounds during exif metadata processing. Organizations should also implement additional defensive measures such as validating and sanitizing all uploaded image files before processing them through PHP applications, implementing strict file type validation, and monitoring for unusual memory access patterns or denial of service conditions. Security practitioners should consider implementing web application firewalls that can detect and block suspicious image file patterns, as well as ensuring that PHP applications are configured to disable exif processing when not required, or to process images through additional validation layers before passing them to the exif extension. This vulnerability demonstrates the importance of proper input validation and memory safety practices in language extensions that handle binary data processing, as it can be leveraged to execute code or extract sensitive information from applications. The ATT&CK framework categorizes this vulnerability under privilege escalation and defense evasion techniques, as attackers can leverage it to gain unauthorized access to system resources or to hide their malicious activities within legitimate application processes.