CVE-2017-12923 in libfpx
Summary
by MITRE
OLEStream::WriteVT_LPSTR in olestrm.cpp 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-2017-12923 represents a critical denial of service flaw within the libfpx library version 1.3.1_p6, specifically within the OLEStream::WriteVT_LPSTR function located in the olestrm.cpp source file. This issue manifests when processing maliciously crafted fpx image files, creating a scenario where remote attackers can induce system instability through NULL pointer dereference conditions. The flaw exists in the handling of variable-length strings during the processing of OLE (Object Linking and Embedding) streams, which are commonly used in various image formats including fpx files that support complex metadata structures. The vulnerability demonstrates the classic pattern of insufficient input validation where the library fails to properly validate the structure and content of incoming fpx data before attempting to process it through the vulnerable write function.
The technical exploitation of this vulnerability occurs when an attacker crafts a specially formatted fpx image file that contains malformed data structures within the OLE stream components. When the libfpx library attempts to process this crafted file through the OLEStream::WriteVT_LPSTR function, it encounters a NULL pointer reference during the string writing operation. This occurs because the function does not adequately check for null or invalid pointers before attempting to dereference them, leading to an immediate system crash or denial of service condition. The vulnerability falls under CWE-476 which specifically addresses NULL pointer dereference issues, and represents a fundamental failure in defensive programming practices where proper input validation and pointer checking mechanisms are absent. The flaw is particularly concerning as it can be triggered remotely through web applications or services that process user-uploaded fpx images without proper sanitization, making it a prime target for exploitation in web-based attack scenarios.
The operational impact of CVE-2017-12923 extends beyond simple service disruption to potentially affect entire applications or systems that rely on libfpx for image processing functionality. When exploited, this vulnerability can cause applications to crash repeatedly, leading to complete service unavailability for legitimate users while attackers maintain the ability to repeatedly exploit the flaw. The remote nature of the attack means that systems processing fpx images from untrusted sources are at risk, including web servers, content management systems, image processing applications, and any software that integrates libfpx for file format handling. This vulnerability directly aligns with ATT&CK technique T1499.004 which covers network denial of service attacks, and demonstrates how seemingly benign file format processing can become a vector for system compromise. The vulnerability affects a wide range of software implementations including web browsers, image viewers, and document processing applications that may incorporate libfpx as part of their image handling capabilities.
Mitigation strategies for CVE-2017-12923 should focus on immediate patching of affected libfpx library versions, implementing proper input validation and sanitization before processing any fpx image files, and establishing robust error handling mechanisms within applications that utilize the library. System administrators should prioritize updating to libfpx versions that contain the patched OLEStream::WriteVT_LPSTR function, which includes proper NULL pointer checks and validation of input data structures. Additionally, implementing network-based filtering to block suspicious fpx file uploads and employing sandboxing techniques for image processing can provide additional layers of protection. Organizations should also consider implementing automated vulnerability scanning tools that can detect the presence of vulnerable libfpx versions in their software environments, and establish incident response procedures specifically designed to handle denial of service attacks targeting image processing libraries. The vulnerability highlights the importance of maintaining up-to-date third-party libraries and implementing comprehensive security testing practices that include fuzzing and input validation testing for all file format processing components within applications.