CVE-2017-13727 in LibTIFF
Summary
by MITRE
There is a reachable assertion abort in the function TIFFWriteDirectoryTagSubifd() in LibTIFF 4.0.8, related to tif_dirwrite.c and a SubIFD tag. A crafted input will lead to a remote denial of service attack.
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Analysis
by VulDB Data Team • 12/27/2022
The vulnerability identified as CVE-2017-13727 represents a critical denial of service weakness within the LibTIFF library version 4.0.8, specifically manifesting in the TIFFWriteDirectoryTagSubifd() function located within the tif_dirwrite.c source file. This flaw occurs in the handling of SubIFD tags, which are specialized directory entries used in TIFF image files to reference additional directory structures. The issue arises when the library encounters a malformed or crafted input containing malicious SubIFD tag data, triggering an assertion abort that terminates the application process. The vulnerability's reachability makes it particularly concerning as it can be exploited remotely through the processing of malicious TIFF files without requiring any special privileges or authentication. This assertion failure stems from improper input validation and error handling within the directory writing functionality, where the function fails to properly validate the structure and content of SubIFD tags before attempting to process them.
The technical exploitation of this vulnerability follows a well-defined pattern that aligns with CWE-617, which addresses reachable assertions and the improper handling of program flow control. When a malicious TIFF file containing specially crafted SubIFD tags is processed by an application linked against the vulnerable LibTIFF library, the TIFFWriteDirectoryTagSubifd() function executes and encounters an assertion condition that fails, causing an immediate program termination. This behavior represents a classic denial of service scenario where legitimate service availability is compromised through controlled application crash conditions. The flaw demonstrates a lack of proper bounds checking and input sanitization, particularly in the context of TIFF file format processing where SubIFD tags are used to create complex hierarchical directory structures. The vulnerability operates at the library level, meaning that any application relying on LibTIFF for TIFF file processing becomes susceptible to this attack vector, regardless of the application's own security measures.
The operational impact of CVE-2017-13727 extends beyond simple service disruption to encompass broader system availability concerns within environments that process TIFF images. Attackers can leverage this vulnerability through various attack vectors including web applications, document processing systems, and image conversion utilities that utilize LibTIFF. The remote nature of the attack means that adversaries can trigger the denial of service condition from external systems without requiring physical access or elevated privileges. This vulnerability particularly affects server applications that accept user-uploaded TIFF files, image processing pipelines, and content management systems that handle TIFF format files. The attack can be executed through multiple delivery mechanisms including email attachments, web uploads, or file sharing systems, making it a versatile threat that can impact diverse software ecosystems. The vulnerability's classification under ATT&CK technique T1499.004 for network denial of service indicates its potential for causing widespread service unavailability across multiple systems that rely on TIFF processing capabilities.
Mitigation strategies for this vulnerability center on immediate library updates and implementation of robust input validation measures. The primary and most effective solution involves upgrading to LibTIFF version 4.0.9 or later, where the assertion abort has been resolved through proper input validation and error handling mechanisms. Organizations should implement comprehensive patch management procedures to ensure all systems processing TIFF files receive the necessary updates promptly. Additionally, implementing strict input validation at application layers can provide defense-in-depth measures, though this approach is less reliable than the core library fix. Network-level mitigations such as file type filtering and sandboxed processing environments can reduce exposure, but these are secondary measures that do not address the root cause. Security teams should also consider implementing automated monitoring for suspicious TIFF file processing activities and establish incident response procedures specifically for handling denial of service attacks targeting image processing libraries. The vulnerability serves as a reminder of the critical importance of maintaining up-to-date third-party libraries and implementing comprehensive security testing practices that include static analysis and dynamic vulnerability assessment of core library functions.