CVE-2017-9094 in ImageWorsener
Summary
by MITRE
The lzw_add_to_dict function in imagew-gif.c in libimageworsener.a in ImageWorsener 1.3.1 allows remote attackers to cause a denial of service (infinite loop) via a crafted image.
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Analysis
by VulDB Data Team • 12/06/2022
The vulnerability identified as CVE-2017-9094 resides within the ImageWorsener library version 1.3.1, specifically in the lzw_add_to_dict function located in the imagew-gif.c file. This flaw represents a classic denial of service vulnerability that can be exploited remotely through the manipulation of specially crafted image files. The issue manifests as an infinite loop during the decompression process of gif images, effectively consuming system resources and rendering the affected application unavailable to legitimate users. The vulnerability stems from improper handling of dictionary construction during lzw decompression, where the algorithm fails to properly validate input parameters before proceeding with dictionary operations. This allows an attacker to craft malicious gif files that, when processed by the vulnerable library, trigger an infinite loop in the lzw_add_to_dict function. The flaw is particularly concerning as it affects the core decompression functionality of the library, meaning any application using ImageWorsener to process gif images becomes vulnerable to this attack vector. The infinite loop consumes cpu cycles continuously without making progress, leading to resource exhaustion and system instability. This vulnerability directly maps to CWE-835, which describes the weakness of an infinite loop or other type of looping construct that does not terminate, and aligns with ATT&CK technique T1499.004, which covers network denial of service through resource exhaustion. The impact extends beyond simple service disruption as the vulnerability can be leveraged in distributed denial of service attacks or to exhaust system resources on servers processing image uploads.
The technical implementation of this vulnerability exploits the lzw decompression algorithm's dictionary management mechanism. During gif decompression, the lzw_add_to_dict function attempts to add new dictionary entries while processing compressed data streams. When an attacker crafts a gif file with malformed lzw data, the function enters a state where it continuously loops without advancing the decompression process. This occurs because the dictionary construction logic does not properly validate whether the current operation would result in an infinite loop condition. The vulnerability is particularly subtle as it does not crash the application outright but rather causes it to become unresponsive, making detection more challenging. The flaw demonstrates poor input validation practices and inadequate bounds checking in the decompression routine, which are fundamental security requirements for handling untrusted data. The vulnerability affects all applications that utilize the ImageWorsener library for gif processing, including web applications, image processing servers, and any software that relies on this library for image manipulation tasks. The remote exploitation aspect means that attackers can trigger this vulnerability without requiring local access, making it a significant threat to online services that process user-uploaded images. This type of vulnerability is classified as a resource exhaustion attack because it consumes computational resources indefinitely, potentially leading to cascading failures in systems that depend on image processing capabilities.
Mitigation strategies for CVE-2017-9094 should focus on both immediate patching and defensive programming practices. The most effective solution involves upgrading to a patched version of ImageWorsener that contains proper bounds checking and loop termination conditions in the lzw_add_to_dict function. Organizations should implement comprehensive vulnerability management processes to identify and remediate similar issues across their software dependencies. Additional protective measures include implementing resource limits on image processing operations, introducing timeout mechanisms for decompression tasks, and employing input validation to detect and reject malformed gif files before they reach the vulnerable library code. Network-level protections such as rate limiting and content filtering can help reduce the impact of exploitation attempts. The vulnerability highlights the importance of robust error handling and input validation in cryptographic and decompression libraries, as these components often process untrusted data from external sources. Security teams should consider implementing automated scanning tools to detect vulnerable library versions and establish monitoring procedures for unusual cpu usage patterns that might indicate exploitation attempts. This vulnerability serves as a reminder of the critical need for thorough testing of decompression algorithms against malformed inputs and the importance of adhering to security best practices such as those outlined in the OWASP Top Ten and NIST guidelines for secure coding practices. The flaw also underscores the necessity of implementing defense-in-depth strategies that include multiple layers of protection to prevent exploitation of similar vulnerabilities in other components of the software stack.