CVE-2016-6237 in Dropbox Lepton
Summary
by MITRE
The build_huffcodes function in lepton/jpgcoder.cc in Dropbox lepton 1.0 allows remote attackers to cause denial of service (out-of-bounds write) via a crafted jpeg file.
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Analysis
by VulDB Data Team • 11/11/2022
The vulnerability identified as CVE-2016-6237 resides within the Dropbox lepton 1.0 image processing library, specifically in the build_huffcodes function located in the lepton/jpgcoder.cc source file. This flaw represents a critical security issue that enables remote attackers to execute denial of service attacks through carefully crafted jpeg files. The vulnerability manifests as an out-of-bounds write condition that occurs during the Huffman code building process, which is fundamental to jpeg compression and decompression operations. When a maliciously formatted jpeg file is processed by the lepton library, the build_huffcodes function fails to properly validate input data boundaries, leading to memory corruption that can crash the application or cause it to behave unpredictably.
The technical implementation of this vulnerability stems from inadequate input validation within the Huffman coding algorithm implementation. Huffman coding requires precise handling of bit streams and code lengths to properly reconstruct compressed data during decompression. The build_huffcodes function processes jpeg header information containing Huffman table definitions without sufficient boundary checks on the number of codes or their assigned values. This deficiency allows attackers to craft jpeg files with malformed Huffman tables that exceed allocated memory boundaries when the function attempts to populate internal data structures. The out-of-bounds write occurs because the function assumes valid input parameters and does not verify that the number of codes specified in the jpeg header matches the actual data available for processing.
From an operational perspective, this vulnerability presents significant risk to systems utilizing Dropbox lepton for image processing tasks, particularly in server environments or applications that accept user-uploaded content. The denial of service impact can be severe as it can cause complete application crashes, requiring system restarts and potentially disrupting services for legitimate users. Attackers can exploit this vulnerability without requiring authentication, making it particularly dangerous in environments where the lepton library processes untrusted input from external sources. The vulnerability affects not only direct usage of lepton but also any applications that depend on it for jpeg processing, creating a wide attack surface across various software ecosystems.
Security practitioners should address this vulnerability through immediate patching of affected lepton versions and implementation of input validation measures. The fix typically involves adding proper boundary checks within the build_huffcodes function to validate the number of Huffman codes and their assigned values before writing to memory locations. Organizations should also consider implementing sandboxing techniques and input sanitization for jpeg files processed through lepton or similar libraries. This vulnerability aligns with CWE-129, which addresses insufficient validation of length of inputs, and represents a classic example of how improper input handling can lead to memory corruption vulnerabilities. The ATT&CK framework categorizes this as a privilege escalation technique through code injection, as the out-of-bounds write can potentially be leveraged to execute arbitrary code if proper memory protection mechanisms are not in place. Additionally, this issue demonstrates the importance of proper software testing including fuzzing techniques to identify boundary condition vulnerabilities in compression libraries that handle complex data structures.