CVE-2017-12920 in libfpx
Summary
by MITRE
CDirectory::GetDirEntry in dir.cxx in libfpx 1.3.1_p6 allows remote attackers to cause a denial of service (NULL pointer dereference) via a crafted fpx image.
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Analysis
by VulDB Data Team • 11/10/2019
The vulnerability identified as CVE-2017-12920 resides within the libfpx library version 1.3.1_p6, specifically in the CDirectory::GetDirEntry function located in the dir.cxx source file. This flaw represents a classic null pointer dereference vulnerability that can be exploited by remote attackers through the careful crafting of malicious fpx image files. The libfpx library serves as a component for handling FlashPix image format processing, which is commonly used in digital imaging applications and document management systems. When a malformed fpx image is processed by software utilizing this library, the vulnerable code path triggers an unexpected null pointer access that results in application termination.
The technical execution of this vulnerability follows a predictable pattern where an attacker crafts an fpx image containing malformed directory entries that cause the CDirectory::GetDirEntry function to attempt dereferencing a null pointer. This occurs during the parsing of the image metadata structure where the function expects certain directory entry fields to contain valid data pointers but encounters null values instead. The flaw aligns with CWE-476 which specifically addresses null pointer dereference conditions, making it a straightforward yet impactful vulnerability that can be exploited without requiring complex attack vectors or privilege escalation. The vulnerability manifests as a denial of service condition rather than arbitrary code execution, meaning that attackers cannot directly execute malicious code but can reliably crash applications that process these image files.
From an operational impact perspective, this vulnerability affects any system or application that relies on libfpx for processing FlashPix images, including document management systems, digital asset management platforms, and imaging software used in enterprise environments. The denial of service nature means that legitimate users may experience application crashes or unresponsiveness when encountering maliciously crafted images, potentially disrupting business operations and creating availability issues. The remote exploit capability further amplifies the risk as attackers can trigger these crashes from external systems without requiring physical access to the target infrastructure, making it particularly dangerous in web-facing applications or systems that automatically process user-uploaded content. This vulnerability can be exploited in various contexts including web applications, email systems, and file sharing platforms where fpx images might be processed automatically.
Mitigation strategies for CVE-2017-12920 should prioritize immediate patching of affected libfpx library versions to the latest stable releases that contain the necessary code fixes. System administrators should implement input validation measures that sanitize or reject malformed fpx images before they reach the processing layer, particularly in applications that handle user-uploaded content. Network-level defenses such as intrusion detection systems can be configured to monitor for suspicious file patterns that might indicate attempts to exploit this vulnerability. Additionally, application developers should implement proper error handling and null pointer checks within their own code to prevent cascading failures when interacting with vulnerable libraries. The vulnerability demonstrates the importance of robust input validation and defensive programming practices, aligning with ATT&CK technique T1203 which covers the exploitation of software vulnerabilities for denial of service attacks. Organizations should also consider implementing sandboxing mechanisms for image processing to contain potential impacts and maintain system availability even when individual components are compromised.