CVE-2019-9721 Denial of service in n/a

What is CVE-2019-9721?

CVE-2019-9721 is a medium-severity denial of service vulnerability in Canonical Ubuntu Linux, published on 12 Mar 2019. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

Official description

A denial of service in the subtitle decoder in FFmpeg 3.2 and 4.1 allows attackers to hog the CPU via a crafted video file in Matroska format, because handle_open_brace in libavcodec/htmlsubtitles.c has a complex format argument to sscanf.

Weakness: CWE-125

Which versions are affected by CVE-2019-9721?

It affects 2 products.

Products include Canonical Ubuntu Linux, Ffmpeg Ffmpeg.

How do I fix CVE-2019-9721?

Apply the vendor's patch.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2019-9721 being exploited?

There is no known exploitation of CVE-2019-9721 in the wild and no public exploit code.

Other vulnerabilities in Canonical Ubuntu Linux

• CVE-2020-11651 SaltStack Salt Authentication Bypass Exploited Critical 9.8
• CVE-2020-7247 OpenSMTPD Remote Code Execution Exploited Critical 9.8
• CVE-2019-16928 Exim Out-of-bounds Write Exploited Critical 9.8
• CVE-2018-6789 Exim Buffer Overflow Exploited Critical 9.8
• CVE-2015-2590 Oracle Java SE and Java SE Embedded Remote Code Execution Exploited Critical 9.8

All Canonical Ubuntu Linux vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as CLEANSTART-2024-EK00824, DEBIAN-CVE-2019-9721, GHSA-hjv9-2v6w-8wp3, JLSEC-2025-103, UBUNTU-CVE-2019-9721.