CVE-2020-13756: Sabberworm PHP CSS Parser before 8.3.1 calls eval on uncontrolled data, possibly leading to remote code execut

Q: How do I fix CVE-2020-13756?

php css parser: upgrade to 8.3.1. Exact commands for each OS are on this page.

Q: Is CVE-2020-13756 being exploited?

CVE-2020-13756 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2020-13756 affect?

CVE-2020-13756 affects php css parser. Severity is critical (CVSS 9.8). Sabberworm PHP CSS Parser before 8.3.1 calls eval on uncontrolled data, possibly leading to remote code execution if the function allSelectors() or getSelectorsBySpecificity() is called with input from an attacker.

Q: How urgent is CVE-2020-13756?

Priority 69/100. Critical severity; EPSS top 1%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action

This week

CRITICAL 9.8REMOTEUPGRADE

CVE-2020-13756 is a critical-severity flaw (CVSS 9.8) affecting php css parser. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Sabberworm PHP CSS Parser before 8.3.1 calls eval on uncontrolled data, possibly leading to remote code execution if the function allSelectors() or getSelectorsBySpecificity() is called with input from an attacker.

Why this priority

Critical severity
EPSS top 1%: very likely to be exploited
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	49.8% (top 1%)
CISA exploited list	No
Weakness	CWE-94
Published	2020-06-03
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: sabberworm

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

Am I affected?

Timeline

2020-06-03 14:15 UTCPublished CVE record published
2026-06-17 02:53 UTCUpdated Record last modified

sabberworm php css parser UPGRADE

Affected: < 8.3.1

Fixed in: 8.3.1

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy php-css-parser || rpm -q php-css-parser || php-css-parser --version

2. UPGRADE to 8.3.1 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade php-css-parser

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade php-css-parser

Note

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

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-2020-13756?

php css parser: upgrade to 8.3.1. Exact commands for each OS are on this page.

Is CVE-2020-13756 being exploited?

CVE-2020-13756 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-2020-13756 affect?

CVE-2020-13756 affects php css parser. Severity is critical (CVSS 9.8). Sabberworm PHP CSS Parser before 8.3.1 calls eval on uncontrolled data, possibly leading to remote code execution if the function allSelectors() or getSelectorsBySpecificity() is called with input from an attacker.

How urgent is CVE-2020-13756?

Priority 69/100. Critical severity; EPSS top 1%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action

Software pages

PHP vulnerabilities

References

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