CVE-2016-8670 in macOS
Summary
by MITRE
Integer signedness error in the dynamicGetbuf function in gd_io_dp.c in the GD Graphics Library (aka libgd) through 2.2.3, as used in PHP before 5.6.28 and 7.x before 7.0.13, allows remote attackers to cause a denial of service (stack-based buffer overflow) or possibly have unspecified other impact via a crafted imagecreatefromstring call.
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Analysis
by VulDB Data Team • 11/03/2022
The CVE-2016-8670 vulnerability represents a critical integer signedness error within the GD Graphics Library's dynamicGetbuf function in the gd_io_dp.c file. This flaw exists in libgd versions through 2.2.3 and affects PHP installations before 5.6.28 and 7.x before 7.0.13, creating a significant security risk that can be exploited remotely. The vulnerability stems from improper handling of integer values during image processing operations, specifically when the library attempts to allocate memory for dynamic buffer operations. The signedness error occurs when negative integer values are incorrectly interpreted as positive values during buffer allocation calculations, leading to memory corruption scenarios. This issue manifests when PHP processes image data through the imagecreatefromstring function, which internally relies on the vulnerable libgd library components.
The technical exploitation of this vulnerability involves crafting malicious image data that triggers the integer signedness error during buffer allocation. When the dynamicGetbuf function processes image data, it performs calculations that can result in negative values being used for memory allocation sizes. These negative values, when interpreted as unsigned integers, can cause the system to attempt allocating extremely large buffer sizes or cause stack-based buffer overflows. The vulnerability is particularly dangerous because it can lead to denial of service conditions where the application crashes due to memory allocation failures, or potentially allow for more sophisticated attacks depending on the specific memory corruption patterns. The flaw is categorized under CWE-191 as an Integer Underflow (Wrap or Wraparound) and can be mapped to ATT&CK technique T1203 for legitimate system exploitation through software vulnerabilities.
The operational impact of CVE-2016-8670 extends beyond simple denial of service scenarios, as it can potentially enable remote code execution in certain configurations where the memory corruption leads to exploitable conditions. Systems running affected PHP versions that process untrusted image uploads or data from external sources become vulnerable to this attack vector. The vulnerability affects web applications that utilize image processing functionality, particularly those accepting user-uploaded images or processing external image data from APIs or third-party services. Organizations using PHP-based web applications, content management systems, or any platform that relies on GD Graphics Library for image handling are at risk. The attack requires minimal privileges and can be executed through standard web requests, making it particularly dangerous for public-facing applications. The vulnerability demonstrates the critical importance of proper input validation and integer handling in graphics processing libraries, as these components often handle untrusted data from network sources.
Mitigation strategies for CVE-2016-8670 involve immediate patching of affected PHP installations and libgd library versions, ensuring that all systems are updated to versions that contain the necessary fixes. Organizations should implement strict image validation and sanitization processes, including MIME type checking, image size restrictions, and content scanning for potentially malicious image data. Network-based mitigations such as web application firewalls can help detect and block suspicious image processing requests, while application-level protections should enforce proper error handling and input validation. The fix typically involves correcting the integer signedness handling in the dynamicGetbuf function to properly validate and handle negative values during buffer allocation calculations. Security monitoring should be implemented to detect unusual memory allocation patterns or application crashes that might indicate exploitation attempts. Regular security assessments and vulnerability scanning should be conducted to identify any remaining instances of vulnerable software in the environment, with particular attention to legacy systems that may not receive timely updates.