html_sanitize_ex HTML5 scrubber keeps attacker-supplied form-association attributes, allowing form hijacking
Summary
| CVE | CVE-2026-66370 |
|---|---|
| State | PUBLISHED |
| Assigner | EEF |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-08-06 16:16:48 UTC |
| Updated | 2026-08-06 22:18:18 UTC |
| 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. |
Risk And Classification
Primary CVSS: v4.0 4.8 MEDIUM from 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
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:X/V:X/RE:X/U:X
Problem Types: CWE-601 | CWE-601 CWE-601 URL Redirection to Untrusted Site ('Open Redirect')
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 4.0 | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | Secondary | 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/E:X/C... |
| 4.0 | CNA | CVSS | 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 |
CVSS v4.0 Breakdown
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:X/V:X/RE:X/U:X
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Rrrene | Html Sanitize Ex | affected 0.3.1 1.5.3 semver | Not specified |
| CNA | Rrrene | Html Sanitize Ex | affected 8976d64ea0b77d26093a94a43ec48a3978e8d028 a1e804ed997e780ea71d14393cf2f701330553a6 git | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| osv.dev/vulnerability/EEF-CVE-2026-66370 | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | osv.dev | |
| github.com/rrrene/html_sanitize_ex/commit/a1e804ed997e780ea71d14393cf2f7... | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | github.com | |
| github.com/rrrene/html_sanitize_ex/security/advisories/GHSA-w3f9-jjhw-wwvq | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | github.com | |
| cna.erlef.org/cves/CVE-2026-66370.html | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | cna.erlef.org | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: Peter Ullrich (en)
CNA: Jonatan Männchen / EEF (en)
CNA: René Föhring (en)
Additional Advisory Data
Workarounds
CNA: Sanitize with basic_html/1, markdown_html/1 or strip_tags/1, none of which allow input, or define a custom scrubber that omits it. Omitting the id attribute from the page's own forms, or giving them values an attacker cannot predict, removes the anchor the injected form attribute needs.