CVE-2019-6284: In LibSass 3.5.5, a heap-based buffer over-read exists in Sass::Prelexer::alternatives in prelexer.hpp.

This month

MEDIUM 6.5DOWNGRADE

CVE-2019-6284 is a medium-severity flaw (CVSS 6.5) affecting libsass. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

In LibSass 3.5.5, a heap-based buffer over-read exists in Sass::Prelexer::alternatives in prelexer.hpp.

Why this priority

Public exploit reference

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	6.5 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	2.0% (top 19%)
CISA exploited list	No
Weakness	CWE-125
Published	2019-01-14
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: sass-lang

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

Am I affected?

Timeline

2019-01-14 22:29 UTCPublished CVE record published
2026-06-17 02:38 UTCUpdated Record last modified

sass-lang libsass DOWNGRADE

Affected: 3.5.5

Fixed in: no fixed release known

Safe to downgrade to: a release before 3.5.5

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 3.5.5 (Debian / Ubuntu)

apt-cache madison libsass sudo apt install libsass=<VERSION_BEFORE_3.5.5> sudo apt-mark hold libsass

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list libsass sudo dnf downgrade libsass-<VERSION_BEFORE_3.5.5> sudo dnf versionlock add libsass

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.

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-2019-6284?

libsass: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2019-6284 being exploited?

CVE-2019-6284 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-2019-6284 affect?

CVE-2019-6284 affects libsass. Severity is medium (CVSS 6.5). In LibSass 3.5.5, a heap-based buffer over-read exists in Sass::Prelexer::alternatives in prelexer.hpp.

How urgent is CVE-2019-6284?

Priority 48/100. Public exploit reference

Related CVEs

CVE-2022-43358 HIGH 7.5 DOWNGRADE Stack overflow vulnerability in ast_selectors.cpp: in function Sass::ComplexSelector::has_placeholder in libsa
CVE-2022-43357 HIGH 7.5 DOWNGRADE DOWNGRADE Stack overflow vulnerability in ast_selectors.cpp in function Sass::CompoundSelector::has_real_parent_ref in l
CVE-2022-26592 HIGH 8.8 DOWNGRADE Stack Overflow vulnerability in libsass 3.6.5 via the CompoundSelector::has_real_parent_ref function.
CVE-2019-6286 MEDIUM 6.5 DOWNGRADE In LibSass 3.5.5, a heap-based buffer over-read exists in Sass::Prelexer::skip_over_scopes in prelexer.hpp whe
CVE-2019-6283 MEDIUM 6.5 DOWNGRADE In LibSass 3.5.5, a heap-based buffer over-read exists in Sass::Prelexer::parenthese_scope in prelexer.hpp.

References

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