Is CVE-2026-126206 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-126206 being exploited in the wild.

How severe is CVE-2026-126206?

Medium severity, published 12 November 2026.

Which products and versions are affected?

Loofah before 2.25.3; Ruby on Rails Rails::HTML::Sanitizer unknown; loofah (RubyGems) = 2.25.2.

How is CVE-2026-126206 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-126206?

Check whether you run Loofah, Ruby on Rails Rails::HTML::Sanitizer or loofah (RubyGems) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-126206: Loofah HTML5 Scrub XSS bypass via HTML entity encoding in data URIs

CVE-2026-126206 · Severity: medium · Published 2026-11-12

Loofah is a library that sanitizes HTML to prevent malicious content. An attacker can bypass its URI validation by encoding special characters as HTML entities (like / for /), causing the library to misidentify a data:text/html URI as the safe text/plain type. This could allow injected JavaScript to execute in users' browsers when an application uses Loofah to validate user-supplied URLs.

Technologies: Loofah, loofah (RubyGems). Vendors: Loofah, Ruby on Rails, RubyGems.

Quick answers

Is CVE-2026-126206 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-126206 being exploited in the wild.
How severe is CVE-2026-126206?: Medium severity, published 12 November 2026.
Which products and versions are affected?: Loofah before 2.25.3; Ruby on Rails Rails::HTML::Sanitizer unknown; loofah (RubyGems) = 2.25.2.
Is there a fix for CVE-2026-126206?: Yes: fixed in Loofah 2.25.3. Until then: Upgrade Loofah to version 2.25.3 or later. Note that the default sanitize() path is not affected as Nokogiri decodes entities during parsing; only direct callers of the allowed_uri? helper with HTML-encoded input are vulnerable. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-126206 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-126206?: Check whether you run Loofah, Ruby on Rails Rails::HTML::Sanitizer or loofah (RubyGems) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

Fixed in: Loofah 2.25.3

Upgrade Loofah to version 2.25.3 or later. Note that the default sanitize() path is not affected as Nokogiri decodes entities during parsing; only direct callers of the allowed_uri? helper with HTML-encoded input are vulnerable.

Technical details

The allowed_uri? method uses CGI.unescapeHTML which only decodes numeric character references, not HTML5 named character references. When / survives normalization, the MIME type lacks a forward slash and is treated as malformed, falling back to the allowed text/plain type. A browser decoding the same entity reads it as text/html, creating a parsing divergence that enables XSS injection via crafted data URIs using &colon;, /, &Tab;, or &NewLine; entities.

Affected products

Loofah Loofah before 2.25.3
Ruby on Rails Rails::HTML::Sanitizer unknown

Identifiers

CVE-2026-126206
GHSA-jcff-cj73-4w4f

Timeline

2026-11-12: disclosed

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