CVE-2017-12962: There are memory leaks in LibSass 3.4.5 triggered by deeply nested code, such as code with a long sequence of

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HIGH 7.5REMOTEDOWNGRADE

CVE-2017-12962 is a high-severity flaw (CVSS 7.5) affecting libsass. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

There are memory leaks in LibSass 3.4.5 triggered by deeply nested code, such as code with a long sequence of open parenthesis characters, leading to a remote denial of service attack.

Why this priority

High severity
Remotely exploitable, no login, no user action

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

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.2% (top 31%)
CISA exploited list	No
Weakness	CWE-772
Published	2017-08-18
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: libsass

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

Am I affected?

Timeline

2017-08-18 21:29 UTCPublished CVE record published
2026-06-17 01:04 UTCUpdated Record last modified

libsass libsass DOWNGRADE

Affected: 3.4.5

Fixed in: no fixed release known

Safe to downgrade to: a release before 3.4.5

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 3.4.5 (Debian / Ubuntu)

apt-cache madison libsass sudo apt install libsass=<VERSION_BEFORE_3.4.5> sudo apt-mark hold libsass

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

dnf --showduplicates list libsass sudo dnf downgrade libsass-<VERSION_BEFORE_3.4.5> 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-2017-12962?

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

Is CVE-2017-12962 being exploited?

CVE-2017-12962 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-2017-12962 affect?

CVE-2017-12962 affects libsass. Severity is high (CVSS 7.5). There are memory leaks in LibSass 3.4.5 triggered by deeply nested code, such as code with a long sequence of open parenthesis characters, leading to a remote denial of service attack.

How urgent is CVE-2017-12962?

Priority 48/100. High severity; Remotely exploitable, no login, no user action

Related CVEs

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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-2019-6284 MEDIUM 6.5 DOWNGRADE In LibSass 3.5.5, a heap-based buffer over-read exists in Sass::Prelexer::alternatives in prelexer.hpp.

References

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