# CVE-2026-126206: Loofah allowed_uri? treats data:text/html as safe text/plain

Status: published. Published: 2026-11-12. Updated: 2026-11-12.

Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. In 2.25.2, Loofah::HTML5::Scrub.allowed_uri? treats a data URI mediatype containing the HTML5 named solidus reference / as malformed and falls back to the allowed text/plain, while a browser decodes the reference and interprets the same value as text/html. An application that validates a user-controlled URL with this helper and renders the approved value in href or another browser-interpreted URI attribute can allow cross-site scripting. Rails::HTML::Sanitizer.allowed_uri? re-exports the affected helper. Loofah's default sanitize() path is not affected because Nokogiri decodes the entity before URI validation. This issue is fixed in version 2.25.3.

## Remediation

- fix: loofah (RubyGems): OSV reports a fixed version 2.25.3. Check the advisory for supported release branches. (source: OSV GHSA-jcff-cj73-4w4f) — https://github.com/advisories/GHSA-jcff-cj73-4w4f

## Affected products and versions

- flavorjones / loofah: = 2.25.2 (affected). Source: CNA: GitHub_M
-  / loofah (loofah): 2.25.2 (affected, RubyGems); Ecosystem version events: introduced 2.25.2; fixed 2.25.3. Source: OSV GHSA-jcff-cj73-4w4f

## Severity and prioritization

- CVSS 4.0: 5.3 (medium); CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N; source: CNA: GitHub_M

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-79, CWE-184

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/flavorjones/loofah/security/advisories/GHSA-jcff-cj73-4w4f (CNA: GitHub_M; x_refsource_CONFIRM)

- https://github.com/flavorjones/loofah/pull/324 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/flavorjones/loofah/commit/ad92002966053309f83b550861e2ef04bc714744 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/flavorjones/loofah/releases/tag/v2.25.3 (CNA: GitHub_M; x_refsource_MISC)

- https://github.com/advisories/GHSA-jcff-cj73-4w4f (OSV / GitHub Security Advisories; advisory)

- https://osv.dev/vulnerability/GHSA-jcff-cj73-4w4f (OSV / GitHub Security Advisories; osv)

## Provenance

- CNA: GitHub_M: https://www.cve.org/CVERecord?id=CVE-2026-126206; retrieved 2026-11-12; source updated 2026-11-12

- OSV / GitHub Security Advisories: https://osv.dev/vulnerability/GHSA-jcff-cj73-4w4f; retrieved 2026-11-12; source updated 2026-11-12

Revision: 1bf56c5067854207c399fd552269d3d809bb259882423272c4dc1ecfea8ad437

Canonical: https://y2.dev/cve/CVE-2026-126206

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