CVE-2026-25543Network attack vector

Cross-site scripting via unsanitized template contents

Published Feb 4, 2026 · Updated Feb 4, 2026

Cross-site scripting in HtmlSanitizer before 9.0.892 and 9.1.878-beta through 9.1.892-beta allows remote attackers to execute browser script. DoSanitize traverses ordinary DOM descendants but skips the separate document fragment stored by an allowed template element, leaving unsafe descendants intact. The default configuration is unaffected; exploitation requires allowing template, after which deep mutation-XSS nesting or an also-allowed shadowrootmode attribute exposes the retained content to a browser.

CVSS severity6.3
Medium
EPSS probability0.25%
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 HtmlSanitizer before 9.0.892 and 9.1.878-beta through 9.1.892-beta allows remote attackers to execute browser script. DoSanitize traverses ordinary DOM descendants but skips the separate document fragment stored by an allowed template element, leaving unsafe descendants intact. The default configuration is unaffected; exploitation requires allowing template, after which deep mutation-XSS nesting or an also-allowed shadowrootmode attribute exposes the retained content to a browser.

The record

CVE
CVE-2026-25543
Published
Feb 4, 2026
Updated
Feb 4, 2026
Vendor
Michael Ganss
Product
HtmlSanitizer
Classifications
CWE-79, CWE-116, T1059.007
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 4, 2026CVE publishedPublication date reported by the CVE source.
  2. Feb 4, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 9.0.892
  2. Affected versionversion=< 9.1.893-beta

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Michael Ganss · HtmlSanitizerversion=< 9.0.892; version=< 9.1.893-beta

Published CVSS scores

6.3GitHub, Inc.CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N
6.1NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CWE-116Improper Encoding or Escaping of Output
T1059.007Command and Scripting Interpreter: JavaScript/JScript

Public exploit references

No public exploit references are available in this record.

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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