CVE-2019-9721 Explained : Impact and Mitigation

CVE-2019-9721 was published on March 12, 2019, and affects FFmpeg versions 3.2 and 4.1. Attackers can exploit a vulnerability in the subtitle decoder to overwhelm the CPU by using a maliciously crafted video file in Matroska format.

Understanding CVE-2019-9721

This CVE involves a denial of service vulnerability in FFmpeg versions 3.2 and 4.1, allowing attackers to consume excessive CPU resources through a specific video file manipulation.

What is CVE-2019-9721?

The vulnerability in the subtitle decoder of FFmpeg versions 3.2 and 4.1 enables attackers to exhaust the CPU by utilizing a specially crafted Matroska video file. The issue originates from the handle_open_brace function in libavcodec/htmlsubtitles.c, where the format argument of sscanf is overly complex.

The Impact of CVE-2019-9721

Exploiting this vulnerability can lead to a denial of service condition, causing the CPU to be overwhelmed and potentially disrupting normal system operations.

Technical Details of CVE-2019-9721

This section provides more in-depth technical insights into the CVE.

Vulnerability Description

The vulnerability allows attackers to hog CPU resources by manipulating a video file in Matroska format due to a complex format argument in the handle_open_brace function.

Affected Systems and Versions

FFmpeg versions 3.2 and 4.1

Exploitation Mechanism

Attackers can exploit the vulnerability by using a specially crafted video file in Matroska format to trigger the CPU overload.

Mitigation and Prevention

Protecting systems from CVE-2019-9721 requires immediate actions and long-term security practices.

Immediate Steps to Take

Update FFmpeg to a patched version that addresses the vulnerability
Avoid opening video files from untrusted or unknown sources

Long-Term Security Practices

Regularly update software and firmware to patch known vulnerabilities
Implement network segmentation to limit the impact of potential attacks

Patching and Updates

Ensure timely installation of security patches and updates for FFmpeg to mitigate the risk of exploitation.