CVE-2016-6236 in Dropbox Lepton
Summary
by MITRE
The setup_imginfo_jpg function in lepton/jpgcoder.cc in Dropbox lepton 1.0 allows remote attackers to cause a denial of service (out-of-bounds read) via a crafted jpeg file.
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Analysis
by VulDB Data Team • 11/11/2022
The vulnerability identified as CVE-2016-6236 resides within the lepton library version 1.0, which is utilized by Dropbox for image processing operations. This flaw manifests in the setup_imginfo_jpg function located in the lepton/jpgcoder.cc source file, representing a critical security weakness that affects the library's ability to handle malformed jpeg image files. The issue specifically enables remote attackers to exploit a buffer over-read condition that can result in system instability and denial of service scenarios.
The technical implementation of this vulnerability stems from inadequate input validation within the jpeg decoding process. When the setup_imginfo_jpg function processes a specially crafted jpeg file, it fails to properly bounds-check array accesses during the parsing of jpeg headers and metadata. This insufficient validation allows attackers to construct malicious jpeg files that contain malformed data structures, particularly within the image information headers. The function does not adequately verify the integrity of jpeg markers or validate the expected data lengths, leading to out-of-bounds memory reads when the parser attempts to access memory locations beyond the allocated buffer boundaries.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as it represents a potential vector for more sophisticated attacks within the Dropbox ecosystem. Remote attackers can leverage this weakness to disrupt legitimate image processing services, potentially affecting thousands of users who rely on Dropbox's file handling capabilities. The vulnerability affects any system that utilizes lepton version 1.0 for jpeg file processing, including web applications and mobile platforms that integrate Dropbox's image handling libraries. This creates a widespread risk across multiple attack surfaces where jpeg files are processed or validated, particularly in cloud storage and file sharing environments.
Mitigation strategies for CVE-2016-6236 should prioritize immediate patching of the lepton library to version 1.1 or later, which contains the necessary fixes for bounds checking and input validation. Organizations should implement comprehensive input sanitization measures that validate jpeg file integrity before processing, including checksum verification and header structure validation. The fix addresses the underlying CWE-129 weakness related to insufficient bounds checking, which aligns with the ATT&CK technique T1059.007 for command and scripting interpreter execution. Additionally, security teams should deploy network monitoring solutions to detect anomalous jpeg file processing patterns and implement automated scanning of uploaded files for known malicious structures. Regular security audits of third-party libraries and dependency management practices should be enforced to prevent similar vulnerabilities from being introduced into production environments.
This vulnerability demonstrates the critical importance of proper memory management and input validation in image processing libraries, particularly in cloud-based services where user-generated content processing is common. The flaw represents a classic example of how seemingly minor input validation gaps can result in significant system instability and service disruption. The security community should recognize this as a prime example of why robust buffer overflow protection mechanisms are essential in multimedia processing libraries, as such vulnerabilities can be exploited to create persistent denial of service conditions that impact service availability and user experience.