CVE-2026-66370
html_sanitize_ex HTML5 scrubber keeps attacker-supplied form-association attributes, allowing form hijacking
- State
- Published
- Severity
- 4.8 Medium
- Published
- Aug 6, 2026
- Updated
- Aug 19, 2026
- Reserved
- Aug 6, 2026
Description
URL Redirection to Untrusted Site ('Open Redirect') vulnerability in the HTML5 scrubber in rrrene html_sanitize_ex allows an unauthenticated remote attacker to retarget a form already on the rendering page and receive whatever the victim submits, including credentials, via the form and formaction attributes on an <input> element in sanitized HTML. HTML's form attribute associates an input with any form on the page by its id even when the input sits outside that form, and formaction on a submit control overrides the owning form's action. Neither attribute receives a scheme check, so an absolute cross-origin URL survives sanitizing.
No script executes. The scrubber allows neither form nor button, so the attacker cannot introduce a form of their own and the rendering page must already contain a form carrying an id.
This issue affects html_sanitize_ex: from 0.3.1 before 1.4.5 and from 1.5.0-rc.0 before 1.5.3.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 4.8 Medium | CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:N/VI:N/VA:N/SC:H/SI:L/SA:N | EEF |
Weaknesses
- CWE-601 URL Redirection to Untrusted Site ('Open Redirect')
Affected Products
| Product | Versions |
|---|---|
html_sanitize_exrrrene |
|
html_sanitize_exrrrene |
|
References
- https://github.com/rrrene/html_sanitize_ex/security/advisories/GHSA-w3f9-jjhw-wwvqvendor-advisoryrelated
- https://cna.erlef.org/cves/CVE-2026-66370.htmlrelated
- https://osv.dev/vulnerability/EEF-CVE-2026-66370related
- https://github.com/rrrene/html_sanitize_ex/commit/a1e804ed997e780ea71d14393cf2f701330553a6patch
- https://github.com/rrrene/html_sanitize_ex/commit/21394e758cb0ffe12fb9953c30fdedc6016c8f9epatch
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