Stored XSS via unescaped entity-decoded option text
Published Apr 15, 2026 · Updated Apr 15, 2026
Stored XSS in sanitize-html 2.17.2 and ApostropheCMS 4.28.0 allows remote attackers to inject tags through sanitized HTML. The ontext handler appends htmlparser2-decoded text from allowed option elements directly to output instead of passing it through escapeHtml, so entity-encoded markup becomes executable HTML. Exploitation requires a non-default allowlist containing option and user interaction when the poisoned content is rendered, enabling script execution in the viewer’s browser.
Summary
What happened
Stored XSS in sanitize-html 2.17.2 and ApostropheCMS 4.28.0 allows remote attackers to inject tags through sanitized HTML. The ontext handler appends htmlparser2-decoded text from allowed option elements directly to output instead of passing it through escapeHtml, so entity-encoded markup becomes executable HTML. Exploitation requires a non-default allowlist containing option and user interaction when the poisoned content is rendered, enabling script execution in the viewer’s browser.
The record
- CVE
- CVE-2026-40186
- Published
- Apr 15, 2026
- Updated
- Apr 15, 2026
- Vendor
- Apostrophe Technologies
- Product
- sanitize-html
- Classifications
- CWE-79, T1203
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 15, 2026CVE publishedPublication date reported by the CVE source.
- Apr 15, 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.
- Affected versionversion=>= 2.17.1, < 2.17.2
What conditions does exploitation require?
What is affected?
Published CVSS scores
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.
Weakness, pattern, technique
Public exploit references
- GHSA-9mrh-v2v3-xpfm option-element XSS proof of conceptproof of concept · demonstrated
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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