CVE-2026-126206
Loofah allowed_uri? treats data:text/html as safe text/plain
CVE-2026-126206 is a medium vulnerability (CVSS 5.3) in Flavorjones Loofah, published November 12, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.42%, the 36th percentile. Fixed in loofah 2.25.3.
- Severity
- 5.3 MediumCVSS 4.0, CVE List
- Exploit chance
- 0.42%EPSS, 36th percentile
- Exploitation
- None knownNot on CISA’s or ENISA’s lists
- Fixed in
2.25.3loofah +8 more
Description
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.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- Passive
What an attacker can affect
- Confidentiality
- None
- Integrity
- None
- Availability
- None
Exploit likelihood
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
loofahRubyGems | 2.25.2 to 2.25.2 | 2.25.3 |
loofahRubyGems | 2.25.2 up to 2.25.3 | 2.25.3 |
ruby-loofahUbuntu:16.04:LTS | All versions, plus listed versions 2.0.2-12.0.3-12.0.3-22.0.3-2+deb9u1build0.16.04.12.0.3-2+deb9u2build0.16.04.12.0.3-2+deb9u3build0.16.04.1 | None known |
ruby-loofahUbuntu:18.04:LTS | All versions, plus listed versions 2.0.3-22.2.2-1 | None known |
ruby-loofahUbuntu:20.04:LTS | All versions, plus listed versions 2.2.3-12.3.1+dfsg-12.4.0+dfsg-1 | None known |
ruby-loofahUbuntu:22.04:LTS | All versions, plus listed versions 2.12.0-12.13.0-12.13.0-2 | None known |
ruby-loofahUbuntu:24.04:LTS | All versions, plus listed versions 2.21.3-12.21.4-12.22.0-1 | None known |
ruby-loofahUbuntu:26.10 | All versions, plus listed versions 2.25.0-12.25.1-22.25.2-1 | None known |
ruby-loofahUbuntu:26.04:LTS | All versions, plus listed versions 2.24.1-12.25.0-1 | None known |
What each source reports
CVE List Score used
Loofah allowed_uri? treats data:text/html as safe text/plain
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.
- Record
CVE-2026-126206- 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 - Weakness
- CWE-79, CWE-184
- Updated
- 2026-11-12
EUVDEUVD-2026-124712
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.
- Record
EUVD-2026-124712- 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 - Updated
- 2026-11-12
GitHub AdvisoriesGHSA-jcff-cj73-4w4f
Loofah allowed_uri? treats data:text/html as safe text/plain
Summary
Loofah::HTML5::Scrub.allowed_uri? returns true for a data: URI whose mediatype is written with the HTML5 named character reference / in place of the solidus. Loofah reads that mediatype as malformed and falls back to the allowed text/plain, while a browser decodes the reference and reads the same URI as text/html.
Details
allowed_uri? decodes HTML entities with CGI.unescapeHTML, which handles numeric character references but not HTML5 named character references. / therefore survives normalization, so the mediatype carries no /, fails the MIME grammar, and falls back to the allowed text/plain under the WHATWG rule for a malformed mediatype.
:, /, 	 and 
 are the only named character references in the HTML5 table that decode to characters that change how a URI parses (U+003A, U+002F, U+0009 and U+000A; there is no named reference for U+000D), so this closes the set.
Loofah's default sanitize() path is not affected, because Nokogiri decodes the entity during parsing before Loofah evaluates the URI. This issue affects only callers of the public allowed_uri? string-level helper that pass it HTML-encoded strings.
Impact
Applications that validate a user-controlled URL with Loofah::HTML5::Scrub.allowed_uri? and then render the approved value into an href or another browser-interpreted URI attribute may be vulnerable to cross-site scripting. Rails::HTML::Sanitizer.allowed_uri? re-exports the same helper.
Mitigation
Upgrade to Loofah >= 2.25.3.
Credit
Responsibly reported by GitHub user @ngpestelos.
- Record
GHSA-jcff-cj73-4w4f- 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 - Weakness
- CWE-79, CWE-184
- Updated
- 2026-11-12
NVD
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.
- Record
CVE-2026-126206- 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/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 - Weakness
- CWE-79, CWE-184
- Updated
- 2026-11-12
OSV
Loofah allowed_uri? treats data:text/html as safe text/plain
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.
- Record
CVE-2026-126206- 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 - Weakness
- CWE-184, CWE-79
- Updated
- 2026-11-14
OSVGHSA-jcff-cj73-4w4f
Loofah allowed_uri? treats data:text/html as safe text/plain
Summary
Loofah::HTML5::Scrub.allowed_uri? returns true for a data: URI whose mediatype is written with the HTML5 named character reference / in place of the solidus. Loofah reads that mediatype as malformed and falls back to the allowed text/plain, while a browser decodes the reference and reads the same URI as text/html.
Details
allowed_uri? decodes HTML entities with CGI.unescapeHTML, which handles numeric character references but not HTML5 named character references. / therefore survives normalization, so the mediatype carries no /, fails the MIME grammar, and falls back to the allowed text/plain under the WHATWG rule for a malformed mediatype.
:, /, 	 and 
 are the only named character references in the HTML5 table that decode to characters that change how a URI parses (U+003A, U+002F, U+0009 and U+000A; there is no named reference for U+000D), so this closes the set.
Loofah's default sanitize() path is not affected, because Nokogiri decodes the entity during parsing before Loofah evaluates the URI. This issue affects only callers of the public allowed_uri? string-level helper that pass it HTML-encoded strings.
Impact
Applications that validate a user-controlled URL with Loofah::HTML5::Scrub.allowed_uri? and then render the approved value into an href or another browser-interpreted URI attribute may be vulnerable to cross-site scripting. Rails::HTML::Sanitizer.allowed_uri? re-exports the same helper.
Mitigation
Upgrade to Loofah >= 2.25.3.
Credit
Responsibly reported by GitHub user @ngpestelos.
- Record
GHSA-jcff-cj73-4w4f- 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 - Weakness
- CWE-184, CWE-79
- Updated
- 2026-11-12
OSVUBUNTU-CVE-2026-126206
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.
- Record
UBUNTU-CVE-2026-126206- 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 - Updated
- 2026-11-13
History
| Recorded | Changed | Sources |
|---|---|---|
| affected, aliases, references | OSV | |
| references | OSV | |
| published | EUVD, NVD | |
| aliases | EUVD | |
| description, products, published, references, severity | CVE List | |
| affected, references | OSV | |
| first indexed | GitHub Advisories |
Dates are when Every CVE recorded each change. Upstream dates may differ.
References
github.com/flavorjones/loofah/security/advisories/GHSA-jcff-cj73-4w4f