CVE-2017-18234 in Exempi
Summary
by MITRE
An issue was discovered in Exempi before 2.4.3. It allows remote attackers to cause a denial of service (invalid memcpy with resultant use-after-free) or possibly have unspecified other impact via a .pdf file containing JPEG data, related to XMPFiles/source/FormatSupport/ReconcileTIFF.cpp, XMPFiles/source/FormatSupport/TIFF_MemoryReader.cpp, and XMPFiles/source/FormatSupport/TIFF_Support.hpp.
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Analysis
by VulDB Data Team • 02/22/2023
The vulnerability identified as CVE-2017-18234 represents a critical security flaw in the Exempi library, a component widely used for handling XMP metadata in various applications including Adobe Acrobat and other PDF processing tools. This issue affects versions prior to 2.4.3 and demonstrates how seemingly benign file processing operations can lead to severe system compromise. The vulnerability specifically resides in the XMPFiles module's handling of TIFF format data within PDF files, exposing applications that rely on Exempi to potential exploitation through crafted malicious PDF documents.
The technical root cause of this vulnerability stems from improper memory management during the processing of JPEG data embedded within PDF files. When Exempi encounters TIFF format data within a PDF document, the library's TIFF_MemoryReader.cpp and TIFF_Support.hpp components execute invalid memcpy operations that result in use-after-free conditions. This memory corruption occurs because the library fails to properly validate the size and structure of TIFF data before attempting to copy memory segments. The flaw exists in the ReconcileTIFF.cpp file where the library attempts to reconcile TIFF metadata with other file formats without adequate bounds checking, creating opportunities for attackers to manipulate memory layout through carefully crafted input data.
The operational impact of this vulnerability extends beyond simple denial of service to potentially enable remote code execution in affected applications. Attackers can exploit this flaw by crafting malicious PDF files containing specially formatted JPEG data that triggers the vulnerable code path when applications attempt to extract metadata. The use-after-free condition creates opportunities for memory corruption that could be leveraged to execute arbitrary code, depending on the target application's memory management and the specific exploitation techniques employed. This vulnerability affects any application that utilizes Exempi for PDF metadata processing, including document management systems, content management platforms, and various enterprise software solutions that handle PDF documents.
The vulnerability aligns with CWE-416, which addresses use-after-free conditions, and demonstrates how improper memory management can create persistent security risks in widely deployed libraries. From an adversarial perspective, this flaw maps to ATT&CK technique T1059.007 for remote code execution and T1499.004 for denial of service, representing significant operational risks for organizations processing untrusted PDF content. Organizations should prioritize immediate patching of Exempi to version 2.4.3 or later, while implementing additional defensive measures such as PDF content filtering and sandboxing mechanisms. Network-based mitigations including content inspection systems and application firewalls can provide additional protection layers, though the most effective approach remains comprehensive patch management across all systems utilizing Exempi components. The vulnerability underscores the importance of thorough input validation and proper memory management in security-critical libraries, particularly those handling complex multimedia file formats that may contain embedded metadata structures.