CVE-2017-8891 in Dropbox Lepton
Summary
by MITRE
Dropbox Lepton 1.2.1 allows DoS (SEGV and application crash) via a malformed lepton file because the code does not ensure setup of a correct number of threads.
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Analysis
by VulDB Data Team • 12/06/2022
The vulnerability identified as CVE-2017-8891 affects Dropbox Lepton version 1.2.1 and represents a denial of service condition that can result in segmentation faults and application crashes. This issue stems from improper thread management within the lepton file processing code, which is a critical component of the Dropbox Lepton library designed for efficient image compression and decompression. The flaw specifically manifests when the software encounters malformed lepton files that do not conform to expected structural parameters, leading to unpredictable behavior during processing operations.
The technical root cause of this vulnerability lies in the insufficient validation of thread setup parameters within the lepton file parsing mechanism. When a malformed file is processed, the application fails to properly initialize or manage the expected number of threads required for concurrent processing operations. This mismanagement creates a scenario where the thread allocation logic either attempts to create an invalid number of threads or fails to properly coordinate thread execution, resulting in memory corruption and subsequent segmentation faults. The vulnerability operates at the intersection of improper resource management and concurrency control, making it particularly dangerous in environments where automated file processing is common.
From an operational perspective, this vulnerability presents significant risks to systems that rely on Dropbox Lepton for image processing workflows. The denial of service condition can be triggered by simply presenting a maliciously crafted lepton file to the application, making it an attractive target for attackers seeking to disrupt services. The impact extends beyond simple application crashes, as the segmentation faults can potentially lead to system instability, resource exhaustion, or even provide a foothold for more sophisticated attacks. The vulnerability is particularly concerning in server environments where multiple file processing operations occur simultaneously, as the thread management issues can cascade and affect overall system performance.
The flaw aligns with CWE-674, which addresses the issue of uncontrolled recursion or improper thread management, and demonstrates how inadequate thread initialization can lead to system instability. From an ATT&CK framework perspective, this vulnerability could be leveraged as part of a broader attack chain, potentially serving as an initial access vector or escalation mechanism. Organizations using Dropbox Lepton should implement immediate mitigations including input validation for lepton files, limiting file processing capabilities, and ensuring proper thread management protocols are in place. The recommended approach involves updating to patched versions of the software, implementing strict file format validation, and monitoring for anomalous thread behavior that may indicate exploitation attempts.
Security practitioners should also consider implementing network-based detection measures to identify potentially malicious lepton files and establish proper access controls around file processing systems. The vulnerability underscores the importance of robust error handling and resource management in concurrent processing applications, particularly those handling untrusted input data. Organizations should conduct thorough vulnerability assessments of systems utilizing Dropbox Lepton to identify any potential exposure and implement comprehensive monitoring strategies to detect and respond to exploitation attempts effectively.