CVE-2021-42576: The bluemonday sanitizer before 1.0.16 for Go, and before 0.0.8 for Python (in pybluemonday), does not properl

Q: How do I fix CVE-2021-42576?

bluemonday: upgrade to 1.0.16; pybluemonday: upgrade to 0.0.8. Exact commands for each OS are on this page.

Q: Is CVE-2021-42576 being exploited?

CVE-2021-42576 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-2021-42576 affect?

CVE-2021-42576 affects bluemonday, pybluemonday. Severity is critical (CVSS 9.8). The bluemonday sanitizer before 1.0.16 for Go, and before 0.0.8 for Python (in pybluemonday), does not properly enforce policies associated with the SELECT, STYLE, and OPTION elements.

Q: How urgent is CVE-2021-42576?

Priority 63/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

This week

CRITICAL 9.8REMOTEUPGRADEUPGRADE

CVE-2021-42576 is a critical-severity flaw (CVSS 9.8) affecting bluemonday, pybluemonday. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The bluemonday sanitizer before 1.0.16 for Go, and before 0.0.8 for Python (in pybluemonday), does not properly enforce policies associated with the SELECT, STYLE, and OPTION elements.

Why this priority

Critical severity
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	1.6% (top 25%)
CISA exploited list	No
Published	2021-10-18
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: microco · python

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

Am I affected?

Timeline

2021-10-18 15:15 UTCPublished CVE record published
2026-06-17 04:09 UTCUpdated Record last modified

microco bluemonday UPGRADE

Affected: < 1.0.16

Fixed in: 1.0.16

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 1.0.16 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade bluemonday

Note

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

python pybluemonday UPGRADE

Affected: < 0.0.8

Fixed in: 0.0.8

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 0.0.8 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade pybluemonday

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-2021-42576?

bluemonday: upgrade to 1.0.16; pybluemonday: upgrade to 0.0.8. Exact commands for each OS are on this page.

Is CVE-2021-42576 being exploited?

CVE-2021-42576 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-2021-42576 affect?

CVE-2021-42576 affects bluemonday, pybluemonday. Severity is critical (CVSS 9.8). The bluemonday sanitizer before 1.0.16 for Go, and before 0.0.8 for Python (in pybluemonday), does not properly enforce policies associated with the SELECT, STYLE, and OPTION elements.

How urgent is CVE-2021-42576?

Priority 63/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

Software pages

Python vulnerabilities

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References

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