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Vulnerability record · CVE-2026-66370 · published 6 August 2026

CVE-2026-66370: Rrrene htmlsanitizeex open redirect vulnerability

Rrrene · Htmlsanitizeex

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.

4.8 CVSS 4.0 Medium EPSS 0.40% · top 68.1% CWE-601 · Open redirect
4.8CVSS 4.0 base score
0.40%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
5References
19 Aug 2026Last modified by NVD

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.

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://cna.erlef.org/cves/CVE-2026-66370.html PatchThird Party Advisory
https://github.com/rrrene/html_sanitize_ex/commit/21394e758cb0ffe12fb9953c30fdedc6016c8f9e
https://github.com/rrrene/html_sanitize_ex/commit/a1e804ed997e780ea71d14393cf2f701330553a6 Patch
https://github.com/rrrene/html_sanitize_ex/security/advisories/GHSA-w3f9-jjhw-wwvq Broken Link
https://osv.dev/vulnerability/EEF-CVE-2026-66370 PatchThird Party Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-66370), CISA KEV, FIRST EPSS (scores of 2026-09-28). This page is refreshed as NVD updates the record.