Vulnerability · Published Aug 6, 2026 · Assigned by EEF

CVE-2026-66370html_sanitize_ex HTML5 scrubber keeps attacker-supplied form-association attributes, allowing form hijacking

Medium 4.8

In plain English

A medium-severity open redirect in html_sanitize_ex from rrrene. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 35% of all known vulnerabilities).

Severity (CVSS 4.0)4.8Medium

Exploit odds (30 days)0.4%top 65.3% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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.

Affected products (as reported)

Vendor	Product	Versions
rrrene	html_sanitize_ex	0.3.1 – before 1.4.51.5.0-rc.0 – before 1.5.3
rrrene	html_sanitize_ex	8976d64ea0b77d26093a94a43ec48a3978e8d028 – before *

Weakness: CWE-601 · 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

In plain English

Official description

Affected products (as reported)

References