CVE-2026-66370html_sanitize_ex HTML5 scrubber keeps attacker-supplied form-association attributes, allowing form hijacking
- 4.8MediumCVSS base score
- 0.40%Exploitation in 30 daysEPSS · top 65% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
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.
Timeline
ID reserved
By EEF
Published
- 13 days later
· 13 days later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| EEFCNA (assigner) | 4.0 | Medium4.8 | 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 |
| NVDNVD · Modified | 4.0 | Medium4.8 | 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 |
- EPSS (exploitation in 30 days)
- 0.40% · top 65% of all CVEs (13 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: Medium 4.8.
Affected products
- affected 0.3.1 – < 1.4.5
- affected 1.5.0-rc.0 – < 1.5.3
- affected 8976d64ea0b77d26093a94a43ec48a3978e8d028 – < *
What to do
Workaround: 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.
References
References5
- https://github.com/rrrene/html_sanitize_ex/security/advisories/GHSA-w3f9-jjhw-wwvq (opens in a new tab)vendor-advisoryrelated
- https://cna.erlef.org/cves/CVE-2026-66370.html (opens in a new tab)related
- https://osv.dev/vulnerability/EEF-CVE-2026-66370 (opens in a new tab)related
- https://github.com/rrrene/html_sanitize_ex/commit/a1e804ed997e780ea71d14393cf2f701330553a6 (opens in a new tab)patch
- https://github.com/rrrene/html_sanitize_ex/commit/21394e758cb0ffe12fb9953c30fdedc6016c8f9e (opens in a new tab)patch
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2026-54081 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2026-66370)Record last updated .