CVE-2020-36430: libass 0.15.x before 0.15.1 has a heap-based buffer overflow in decode_chars (called from decode_font and proc

This month

HIGH 7.8UPGRADEMITIGATE

CVE-2020-36430 is a high-severity flaw (CVSS 7.8) affecting libass, fedora. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

libass 0.15.x before 0.15.1 has a heap-based buffer overflow in decode_chars (called from decode_font and process_text) because the wrong integer data type is used for subtraction.

Why this priority

High severity

A fixed release or distro patch exists.

Risk facts

CVSS score	7.8 (High)
Attack vector	Local
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	1.1% (top 35%)
CISA exploited list	No
Weakness	CWE-787
Published	2021-07-20
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: fedoraproject · libass project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-07-20 07:15 UTCPublished CVE record published
2026-06-17 03:15 UTCUpdated Record last modified

libass project libass UPGRADE

Affected: >= 0.15.0 and < 0.15.1

Fixed in: 0.15.1

Safe to downgrade to: a release before 0.15.0

1. Check installed version

apt-cache policy libass || rpm -q libass || libass --version

2. UPGRADE to 0.15.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade libass

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade libass

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 0.15.0 (Debian / Ubuntu)

apt-cache madison libass sudo apt install libass=<VERSION_BEFORE_0.15.0> sudo apt-mark hold libass

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list libass sudo dnf downgrade libass-<VERSION_BEFORE_0.15.0> sudo dnf versionlock add libass

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

fedoraproject fedora MITIGATE

Affected: 34

Fixed in: no fixed release known

Safe to downgrade to: a release before 34

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2020-36430?

libass: upgrade to 0.15.1; fedora: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-36430 being exploited?

CVE-2020-36430 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2020-36430 affect?

CVE-2020-36430 affects libass, fedora. Severity is high (CVSS 7.8). libass 0.15.x before 0.15.1 has a heap-based buffer overflow in decode_chars (called from decode_font and process_text) because the wrong integer data type is used for subtraction.

How urgent is CVE-2020-36430?

Priority 44/100. High severity

Related CVEs

CVE-2020-26682 HIGH 8.8 DOWNGRADE In libass 0.14.0, the `ass_outline_construct`'s call to `outline_stroke` causes a signed integer overflow.
CVE-2020-24994 HIGH 8.8 UPGRADE Stack overflow in the parse_tag function in libass/ass_parse.c in libass before 0.15.0 allows remote attackers
CVE-2016-7972 HIGH 7.5 MITIGATE MITIGATE The check_allocations function in libass/ass_shaper.c in libass before 0.13.4 allows remote attackers to cause
CVE-2016-7970 HIGH 7.5 MITIGATE UPGRADE Buffer overflow in the calc_coeff function in libass/ass_blur.c in libass before 0.13.4 allows remote attacker
CVE-2016-7969 HIGH 7.5 MITIGATE MITIGATE The wrap_lines_smart function in ass_render.c in libass before 0.13.4 allows remote attackers to cause a denia

References

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