CVE-2020-21595 in libde265
Summary
by MITRE • 09/17/2021
libde265 v1.0.4 contains a heap buffer overflow in the mc_luma function, which can be exploited via a crafted a file.
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Analysis
by VulDB Data Team • 09/19/2021
The vulnerability CVE-2020-21595 represents a critical heap buffer overflow flaw in libde265 version 1.0.4, a widely used library for decoding h265/HEVC video streams. This library serves as a fundamental component in numerous multimedia applications, video players, and content delivery systems across various operating systems and platforms. The flaw specifically resides within the mc_luma function, which handles motion compensation operations during video decoding processes. Motion compensation is a core technique in video compression standards that predicts pixel values based on previous frames to reduce data redundancy. The buffer overflow occurs when the library processes malformed or crafted video files that contain maliciously constructed motion vector data, causing the application to write beyond allocated memory boundaries in the heap memory region.
The technical exploitation of this vulnerability demonstrates a classic heap-based buffer overflow pattern that can lead to arbitrary code execution or application crashes. The mc_luma function processes luminance data during motion compensation, and when it encounters improperly formatted input data, it fails to validate the size of motion vectors or the boundaries of allocated memory buffers. This lack of proper bounds checking allows attackers to craft specially designed h265 video files that trigger memory corruption when the library attempts to perform motion compensation calculations. The vulnerability is particularly concerning because it can be triggered through standard file-based attacks, meaning that simply opening or processing a maliciously crafted video file can lead to system compromise. The heap overflow occurs during the decoding process when the library attempts to copy or manipulate data structures containing motion vector information that exceeds the allocated buffer size, potentially overwriting adjacent memory regions including function pointers, return addresses, or other critical program data structures.
From an operational impact perspective, this vulnerability affects a broad range of applications and systems that depend on libde265 for video decoding functionality. The flaw impacts multimedia applications, streaming platforms, video processing software, content management systems, and any system that handles h265 video content. The attack surface is extensive since libde265 is integrated into numerous open source projects, commercial software solutions, and operating system components. Security researchers have classified this vulnerability according to CWE-121, which describes heap-based buffer overflow conditions where insufficient boundary checks allow writing beyond allocated heap memory. The potential for remote code execution makes this a severe threat vector, as attackers can deliver malicious video content through various channels including email attachments, web downloads, or streaming services. The vulnerability also aligns with ATT&CK technique T1203, which covers exploitation of software vulnerabilities for privilege escalation or system compromise.
Mitigation strategies for CVE-2020-21595 should prioritize immediate patching of affected libde265 installations to version 1.0.5 or later, which contains the necessary fixes for the buffer overflow issue. System administrators should implement strict input validation for all video content processing pipelines, particularly when dealing with untrusted files from external sources. Network-based defenses can include content filtering solutions that scan video files for known malicious patterns or suspicious motion vector structures. The implementation of memory safety mechanisms such as stack canaries, address space layout randomization, and heap protection features can provide additional defense-in-depth layers. Organizations should also conduct comprehensive vulnerability assessments to identify all systems using libde265 and ensure proper patch management procedures are in place. Additionally, monitoring for unusual network traffic patterns or system behavior that might indicate exploitation attempts can help detect potential attacks. The vulnerability highlights the importance of robust input validation in multimedia processing libraries and serves as a reminder of the critical security considerations required for video codec implementations that handle complex compression algorithms and data structures.