What is CVE-2021-29272?

CVE-2021-29272 is a medium-severity vulnerability in Microco Bluemonday, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2021-03-27.

How severe is CVE-2021-29272?

Medium severity. CVSS v3 base score is 6.1 out of 10.

Is CVE-2021-29272 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

XSS in Microco Bluemonday

CVE-2021-29272

bluemonday before 1.0.5 allows XSS because certain Go lowercasing converts an uppercase Cyrillic character, defeating a protection mechanism against the "script" string.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2021-03-27 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.009 (59.0th percentile), scored 2026-09-29.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 59th percentile — 59.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.009 · newest: 0.009 · change: 0.000

Affected products

Microco Bluemonday

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

Public proof-of-concept exploits

n0-traces/cve_

References

github.com/microcosm-cc/bluemonday/releases/tag/v1.0.5 (Third Party Advisory)
vuln.ryotak.me/advisories/4 (Third Party Advisory)

Frequently asked questions

What is CVE-2021-29272?: CVE-2021-29272 is a medium-severity vulnerability in Microco Bluemonday, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2021-03-27.
How severe is CVE-2021-29272?: Medium severity. CVSS v3 base score is 6.1 out of 10.
Is CVE-2021-29272 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.