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Vulnerabilities CVE-2026-66370

CVE-2026-66370

Medium
Open
TLP:CLEAR

html_sanitize_ex HTML5 scrubber keeps attacker-supplied form-association attributes, allowing form hijacking

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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 1.5.3.

Details

CVSS Score
4.8
EPSS Score
0.23%

13.9th percentile

CVSS Vector
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
Confidence
90%
Published
Aug 6, 2026
Last Modified
Aug 6, 2026
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