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Fencer Vulns
critical 9.8

CVE-2021-42576 json

Policies not properly enforced in bluemonday

published 2021-10-18 5 y ago modified 2026-06-17 4 mo ago also GHSA-x95h-979x-cf3j , GO-2022-0588 , PYSEC-2021-849 , EUVD-2021-0205

cvss
9.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.6%
EPSS 1.6% chance of exploitation in 30 days, percentile 75%
public exploits
0
none known

Summary

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.

Patch / fix

  • pypi pybluemonday 0.0.8
  • go github.com/microcosm-cc/bluemonday 1.0.16
  • microco bluemonday 1.0.16
  • python pybluemonday 0.0.8
  • golang-github-microcosm-cc-bluemonday Debian 14, Debian 13, Debian 12 1.0.16-1

debian advisories DEBIAN-CVE-2021-42576

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-42576 updated cvss 9.8

bluemonday: improper policies enforcement may lead to remote code execution

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.56% chance of exploitation in the next 30 days, higher than 75% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • docs.google.com https://docs.google.com/document/d/11SoX296sMS0XoQiQbpxc5pNxSdbJKDJkm5BDv0zrX50/ referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P
GitHub 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected packages

ecosystem package affected fixed in
pypi pybluemonday
<0.0.8
0.0.8
go github.com/microcosm-cc/bluemonday
<1.0.16
1.0.16

Classification

Weakness
  • CWE-20 Improper Input Validation

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.