CVE-2016-4542 in PHP
Summary
by MITRE
The exif_process_IFD_TAG function in ext/exif/exif.c in PHP before 5.5.35, 5.6.x before 5.6.21, and 7.x before 7.0.6 does not properly construct spprintf arguments, which allows remote attackers to cause a denial of service (out-of-bounds read) or possibly have unspecified other impact via crafted header data.
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Analysis
by VulDB Data Team • 08/22/2022
The vulnerability identified as CVE-2016-4542 represents a critical buffer over-read flaw in PHP's exif extension that affects multiple version lines including 5.5.x, 5.6.x, and 7.x series. This issue stems from improper argument construction within the exif_process_IFD_TAG function located in ext/exif/exif.c, creating a scenario where maliciously crafted EXIF header data can trigger unexpected behavior in the PHP runtime environment. The flaw manifests when PHP processes image files containing specially crafted EXIF metadata, particularly affecting applications that utilize the exif_read_data function to parse image metadata. The vulnerability operates at the intersection of memory management and input validation, where insufficient bounds checking allows attackers to manipulate the spprintf function's arguments and potentially access memory outside of intended boundaries.
The technical exploitation of this vulnerability occurs through careful construction of EXIF header data that causes the exif_process_IFD_TAG function to miscalculate buffer sizes or argument sequences when processing image metadata. When PHP encounters malformed EXIF data, the improper argument handling in spprintf leads to out-of-bounds memory reads that can result in application crashes or potentially more severe consequences depending on the execution context. This type of vulnerability falls under the CWE-121 category of Stack-based Buffer Overflow, though the specific implementation involves heap manipulation through improper argument construction. The attack vector requires an attacker to upload or process an image file containing crafted EXIF data, making it particularly relevant in web applications that accept user-uploaded images or process external image sources without proper validation.
The operational impact of CVE-2016-4542 extends beyond simple denial of service scenarios, as the out-of-bounds memory access could potentially be leveraged for more sophisticated attacks depending on the system configuration and memory layout. While the primary effect is described as denial of service through out-of-bounds read conditions, the unspecified other impacts mentioned in the vulnerability description suggest potential for information disclosure or arbitrary code execution in certain environments. Applications that process untrusted image data, such as content management systems, file upload portals, or image processing services, become particularly vulnerable to this flaw. The vulnerability affects the core PHP processing pipeline and can impact any application utilizing the exif extension, making it a widespread concern across the PHP ecosystem.
Mitigation strategies for CVE-2016-4542 primarily focus on immediate version upgrades to patched PHP releases including 5.5.35, 5.6.21, and 7.0.6, which contain the necessary code modifications to properly handle spprintf argument construction. Organizations should implement comprehensive patch management processes to ensure all affected PHP installations receive updates promptly, particularly given the remote exploitability of this vulnerability. Additional protective measures include implementing input validation for image uploads, sanitizing EXIF metadata before processing, and configuring web applications to limit image file processing capabilities where possible. Security monitoring should be enhanced to detect unusual patterns in image processing operations that might indicate exploitation attempts, and network segmentation can help limit the potential impact of successful attacks. This vulnerability aligns with ATT&CK technique T1203 by enabling remote code execution through application vulnerabilities, and represents a classic example of how improper input handling can create severe security implications in widely deployed software components.