CVE-2021-42575Public exploitNetwork attack vector

Cross-site scripting via nested STYLE parsing

Published Oct 18, 2021 · Updated Aug 4, 2024

Cross-site scripting in OWASP Java HTML Sanitizer before 20211018.1 allows remote attackers to execute script via crafted HTML. When a custom policy permits SELECT, OPTION, and STYLE, the sanitizer fails to close special elements nested in SELECT, causing embedded script to be parsed as executable mixed content. The flaw requires a custom policy allowing all three elements; stock policies are unaffected, and execution occurs in a browser that renders the sanitized output.

CVSS severity9.8
Critical
EPSS probability2.97%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in OWASP Java HTML Sanitizer before 20211018.1 allows remote attackers to execute script via crafted HTML. When a custom policy permits SELECT, OPTION, and STYLE, the sanitizer fails to close special elements nested in SELECT, causing embedded script to be parsed as executable mixed content. The flaw requires a custom policy allowing all three elements; stock policies are unaffected, and execution occurs in a browser that renders the sanitized output.

The record

CVE
CVE-2021-42575
Published
Oct 18, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-20, T1059.007
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 18, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-20Improper Input Validation
T1059.007JavaScript/JScript

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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