CVE-2017-14796 in libbpg
Summary
by MITRE
The hevc_write_frame function in libbpg.c in libbpg 0.9.7 allows remote attackers to cause a denial of service (integer underflow and application crash) or possibly have unspecified other impact via a crafted BPG file, related to improper interaction with copy_CTB_to_hv in hevc_filter.c in libavcodec in FFmpeg and sao_filter_CTB in hevc_filter.c in libavcodec in FFmpeg.
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Analysis
by VulDB Data Team • 11/20/2019
The vulnerability identified as CVE-2017-14796 represents a critical integer underflow condition affecting the libbpg library version 0.9.7, specifically within the hevc_write_frame function in libbpg.c. This flaw demonstrates how improper input validation can lead to severe system instability and potential security implications. The vulnerability arises from the improper interaction between the hevc_write_frame function and other components within the FFmpeg ecosystem, particularly copy_CTB_to_hv and sao_filter_CTB functions located in hevc_filter.c files. The integer underflow occurs when processing crafted BPG files that contain maliciously constructed data, leading to predictable memory access violations that can result in application crashes and denial of service conditions.
The technical exploitation of this vulnerability involves crafting a specially formatted BPG file that triggers the integer underflow during frame processing operations. When the hevc_write_frame function processes such malformed input, it fails to properly validate integer values before performing arithmetic operations, resulting in negative integer values that cause buffer overflows or memory corruption. This type of vulnerability falls under CWE-191, Integer Underflow (Wrap or Wraparound), which is classified as a fundamental flaw in integer arithmetic handling. The interaction with FFmpeg's internal components creates a complex attack surface where the vulnerability in libbpg can propagate through the media processing pipeline, affecting downstream applications that rely on FFmpeg for video decoding operations.
From an operational impact perspective, this vulnerability poses significant risks to systems processing multimedia content, particularly those handling user-uploaded files or remote media streams. The denial of service aspect means that legitimate users could be denied access to services that depend on proper media processing capabilities, while the potential for unspecified other impacts suggests that attackers might be able to leverage this condition for more advanced exploitation techniques. The vulnerability affects not just the immediate library but the entire FFmpeg ecosystem, as the flawed interaction occurs at the interface level between libbpg and FFmpeg's video processing components. This creates a cascading effect where a single vulnerable component can compromise the stability of applications across multiple domains including media servers, content delivery networks, and multimedia processing platforms.
The mitigation strategies for CVE-2017-14796 primarily involve updating to patched versions of libbpg and FFmpeg, as the vulnerability has been addressed through proper integer validation and bounds checking in subsequent releases. Organizations should implement strict input validation for all multimedia file processing operations and consider deploying sandboxing mechanisms to isolate media processing components from critical system resources. Additionally, the vulnerability highlights the importance of proper code review processes focusing on integer arithmetic operations and the need for comprehensive testing of edge cases in multimedia processing libraries. Security practitioners should also consider implementing network segmentation and file type validation to prevent malicious BPG files from reaching vulnerable systems, while monitoring for unusual application behavior that might indicate exploitation attempts. The ATT&CK framework categorizes this vulnerability under the T1203 - Exploitation for Client Execution tactic, as it represents a classic example of how library-level vulnerabilities can be exploited to compromise application stability and potentially enable further attacks.