CVE-2011-0708 in PHP
Summary
by MITRE
exif.c in the Exif extension in PHP before 5.3.6 on 64-bit platforms performs an incorrect cast, which allows remote attackers to cause a denial of service (application crash) via an image with a crafted Image File Directory (IFD) that triggers a buffer over-read.
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Analysis
by VulDB Data Team • 10/14/2024
The vulnerability identified as CVE-2011-0708 represents a critical buffer over-read flaw within PHP's Exif extension that specifically affects 64-bit systems running PHP versions prior to 5.3.6. This issue stems from improper type casting operations within the exif.c source file, which governs how PHP processes Exchangeable Image File Format metadata. The flaw manifests when PHP encounters an image file containing a maliciously crafted Image File Directory structure that exploits the incorrect cast to trigger memory access violations. The vulnerability operates at the intersection of memory management and file parsing, where the Exif extension fails to properly validate the size and structure of IFD entries before attempting to read them into memory buffers.
The technical implementation of this vulnerability exploits fundamental weaknesses in PHP's memory handling during image metadata processing. When the Exif extension parses an image file, it performs type casting operations that assume certain data structures will conform to expected sizes and formats. However, on 64-bit platforms, the casting behavior differs from 32-bit systems, leading to situations where a 32-bit value is incorrectly interpreted as a 64-bit value during buffer allocation. This misinterpretation causes the application to attempt reading beyond the bounds of allocated memory regions, resulting in segmentation faults and application crashes. The vulnerability specifically targets the IFD parsing logic where directory entries are processed sequentially, and a single malformed entry can cause the entire parsing routine to fail catastrophically.
The operational impact of CVE-2011-0708 extends beyond simple denial of service to potentially enable more sophisticated attack vectors when combined with other vulnerabilities. Remote attackers can leverage this flaw to systematically crash web applications that process user-uploaded images, effectively rendering the application unavailable to legitimate users. The vulnerability affects any PHP application that utilizes the Exif extension for image processing, including content management systems, image galleries, and file upload handlers. From an attacker's perspective, this represents a low-effort method to disrupt services, as the malicious IFD structure can be crafted using existing image manipulation tools or specialized software designed to generate malformed image metadata. The vulnerability's persistence across multiple PHP installations makes it particularly dangerous in environments where multiple applications rely on shared PHP configurations.
Mitigation strategies for CVE-2011-0708 primarily focus on immediate version upgrades to PHP 5.3.6 or later, which contain the necessary patches to address the type casting issue in exif.c. Organizations should also implement input validation measures that filter or reject images with suspicious metadata structures before they reach the Exif parsing layer. Security practitioners should consider implementing web application firewalls that can detect and block requests containing known malicious image patterns, while also monitoring for unusual application crash patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-121, which describes buffer overflow conditions, and represents a specific manifestation of improper type handling in memory management contexts. From an ATT&CK framework perspective, this vulnerability maps to the privilege escalation and denial of service tactics, as it allows attackers to compromise system availability through crafted input. Organizations should also implement regular security assessments to identify other potential vulnerabilities in image processing pipelines and ensure that all PHP extensions are regularly updated to prevent similar issues from arising in the future.