CVE-2015-7506 in Libnsgif
Summary
by MITRE
The gif_next_LZW function in libnsgif.c in Libnsgif 0.1.2 allows context-dependent attackers to cause a denial of service (out-of-bounds read and application crash) via a crafted LZW stream in a GIF file.
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Analysis
by VulDB Data Team • 04/22/2023
The vulnerability identified as CVE-2015-7506 resides within the libnsgif library version 0.1.2, specifically in the gif_next_LZW function located in the libnsgif.c source file. This flaw represents a classic out-of-bounds read condition that occurs when processing specially crafted LZW (Lempel-Ziv-Welch) compressed data streams within GIF image files. The issue manifests as a context-dependent vulnerability, meaning that the attack vector requires specific conditions to be met for exploitation to occur, typically involving the manipulation of the LZW compression algorithm's internal state during GIF file parsing.
The technical implementation of this vulnerability stems from inadequate bounds checking within the LZW decompression routine. When the gif_next_LZW function processes a malformed GIF file containing crafted LZW stream data, it fails to properly validate array indices or buffer boundaries before accessing memory locations. This deficiency allows an attacker to manipulate the decompression process such that memory reads occur beyond the allocated buffer boundaries, resulting in unpredictable behavior including application crashes and potential information disclosure. The vulnerability operates at the intersection of data parsing and memory management, making it particularly dangerous in applications that process untrusted image content.
From an operational impact perspective, this vulnerability can be leveraged by context-dependent attackers to execute denial of service attacks against systems processing GIF files through the affected libnsgif library. The consequences extend beyond simple service interruption, as applications utilizing this library may experience complete application crashes, leading to system instability and potential denial of service for legitimate users. The vulnerability affects any software that incorporates libnsgif for GIF image processing, including web browsers, image viewers, and content management systems that handle GIF file uploads or display. The out-of-bounds read condition can potentially be exploited to extract sensitive memory information, though the primary impact remains focused on service disruption.
Mitigation strategies for CVE-2015-7506 should prioritize immediate patching of the affected libnsgif library to version 0.1.3 or later, which contains the necessary bounds checking fixes. Organizations should implement defensive programming practices including input validation, memory safety checks, and proper error handling when processing image files. The vulnerability aligns with CWE-129, which describes improper validation of array indices, and can be mapped to ATT&CK technique T1499.004 for denial of service through resource exhaustion. Additionally, implementing sandboxing mechanisms and restricting GIF file processing to trusted sources can provide additional layers of protection. Network-level defenses such as web application firewalls and content filtering systems should also be configured to scan for and block suspicious GIF file content, particularly in environments where user-generated content is accepted.