GHSA-jcff-cj73-4w4f

Loofah allowed_uri? treats data:text/html as safe text/plain

Products / packages flavorjones loofah · loofah

Published 12/11/2026, 20:51:36 UTC

Severity and exploitation

Not in CISA KEVSource: MODERATE

KEV coverage does not rule out exploitation.

KEV checked 15/11/2026, 04:00:32 UTC

OSV · CVSS:4.0 · 5.3

Assessment vector

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

GitHub_M · CVSS:4.0 · 5.3

Assessment vector

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

The headline uses the highest imported catalog score. Assessments can differ by source and CVSS version.

Severity

medium5.3

CVSS measures technical severity, not the likelihood of an attack.

Known exploitation

Not listed in the checked CISA KEV catalog

Absence from CISA KEV does not rule out attacks.

Public exploit

Not established by this record

Missing evidence does not mean no public exploit exists.

Remediation

Package fixes recorded

Fix versions are recorded for 1 of 1 mapped packages. Check each release branch and any separate product guidance.

What this means

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.

Source excerpt · OSV

Attack conditions

No attack-condition excerpt has been identified here. Review the full source description and references for authentication, network access, and configuration requirements.

Review supporting sources →

Affected versions

Check the exact model, release, and any platform requirements against your installation.

flavorjones · GitHub_M

loofah

1 range

GitHub_M version evidence

Check a product version

Compare with this publisher’s ranges. This does not inspect your installation.

affected

= 2.25.2

Other versions: unknown

Packages

Compare each installed version with the publisher’s affected ranges. Where a fix is recorded, choose the appropriate release branch and test compatibility before upgrading.

loofah RubyGems

Affected range	Recorded fix
From 2.25.2 before 2.25.3Ecosystem versions	2.25.3

Version evidence: OSV · GHSA-jcff-cj73-4w4f

View original version evidence (1 explicit versions)

What to do

Compare your installed product and version with the affected versions above. A matching product name alone does not confirm exposure.

Use the recorded fix for your release branch. Review the publisher’s instructions and test compatibility before upgrading.

cve.new guidance unless attributed to a publisher. This page does not inspect your installation.

Public exploit evidence

No public exploit reference is identified in the imported evidence. This is not a claim that no exploit exists.

Original source description

Read the full publisher description

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.

&colon;, /, &Tab; and &NewLine; 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.

References

6 sources

flavorjones/loofah · security/advisories/GHSA-jcff-cj73-4w4f

Security advisoryGitHub_M

flavorjones/loofah · pull request #324

PatchGitHub_M

flavorjones/loofah · commit ad92002

PatchGitHub_M

flavorjones/loofah · repository

Source reference

flavorjones/loofah · releases/tag/v2.25.3

Release notesGitHub_M

rubysec/ruby-advisory-db · GHSA-jcff-cj73-4w4f.yml

Source reference

Inside the record

Evidence available

Package identity

Version evidence

Remediation guidance · not supplied

Weakness classification

Additional publishers

Describes the evidence in this view, not whether the product is safe.

Original records

CVE-2026-126206

View the latest unmodified CVE JSON from the official source. It may be newer than this imported page.

cve.new JSON →

Underlying weaknesses

The source’s classification of what caused the vulnerability.

CWE-79 ↗

CWE-79: Improper Neutralization of Input During Web Page Generation

GitHub_M

CWE-184 ↗

CWE-184: Incomplete List of Disallowed Inputs

GitHub_M

Contributing organizations · 2

GitHub_M

Assigning organization

2026-11-12

CISA-ADP

Additional data publisher

2026-11-13

Timeline

All times UTC

12 Nov 2026, 20:51
Advisory published
Publication date supplied by the source.
13 Nov 2026, 22:32
Source updated
Latest modification date supplied by the source.
13 Nov 2026, 23:01
Last imported by cve.new
Latest catalog import, not the date we first saw this advisory.

What changed

Follow changes

CVE · CVE-2026-1262062026-11-13

Observed 2026-11-13T23:01:42.719Z · upstream updated 2026-11-13T22:32:32.734Z

Prioritization updated

before

[]

after

[
  {
    "source": "CISA-ADP",
    "type": "SSVC",
    "role": "CISA Coordinator",
    "timestamp": "2026-11-13T16:33:59.076823Z",
    "decisions": [
      {
        "name": "Exploitation",
        "value": "none"
      },
      {
        "name": "Automatable",
        "value": "yes"
      },
      {
        "name": "Technical Impact",
        "value": "partial"
      }
    ]
  }
]

Large field values are marked as truncated previews. Original source snapshots remain retained.

Showing up to 50 most recent observed changes.

Reading the signals

Severity · CVSS: Technical impact and attack conditions. The headline is the highest imported catalog score; sources may disagree.
Observed exploitation · KEV: An absent or unavailable KEV listing does not establish that exploitation has not occurred.
Predicted exploitation · EPSS: No EPSS estimate available in this record.

CISA-ADP · SSVC

CISA Coordinator · 2026-11-13

Exploitation: none
Automatable: yes
Technical Impact: partial

SSVC describes the publisher’s decision context. Your organization’s exposure and priorities may differ.

Record identifiers

Aliases: CVE-2026-126206

Source evidence

Request a correction or dispute

Start with the assigning organization for this record. Include the CVE ID, the disputed information, and supporting evidence. A dispute does not itself reject a record.

Find the responsible CNA →Official dispute and escalation process ↗

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

Enrichment coverage

NVDAvailable

Checked 12/11/2026, 23:05:34 UTC

GHSAAvailable

Checked 12/11/2026, 23:05:35 UTC

EUVDAvailable

Checked 12/11/2026, 23:05:35 UTC

EPSSNo result

Checked 12/11/2026, 23:05:34 UTC

Additional source evidence

NVD · CVE-2026-126206

CVSS 5.3 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

Checked 12/11/2026, 23:05:34 UTC

GitHub Advisory Database · GHSA-jcff-cj73-4w4fChecked 12/11/2026, 23:05:35 UTC

ENISA EUVD · EUVD-2026-124712

CVSS 5.3 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

Checked 12/11/2026, 23:05:35 UTC

Sponsored by MoxsoBuild security habits with adaptive training and phishing simulations.View as JSON

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Loofah allowed_uri? treats data:text/html as safe text/plain

Severity and exploitation

What this means

Attack conditions

Affected versions

loofah

affected

unaffected

unknown

Packages

What to do

Public exploit evidence

Original source description

Summary

Details

Impact

Mitigation

Credit

References

Inside the record

Evidence available

Original records

Underlying weaknesses

Timeline

Advisory published

Source updated

Last imported by cve.new

What changed

Loofah allowed_uri? treats data:text&sol;html as safe text/plain

Severity and exploitation

What this means

Attack conditions

Affected versions

loofah

affected

unaffected

unknown

Packages

What to do

Public exploit evidence

Original source description

Summary

Details

Impact

Mitigation

Credit

References

Inside the record

Evidence available

Original records

Underlying weaknesses

Timeline

Advisory published

Source updated

Last imported by cve.new

What changed

Loofah allowed_uri? treats data:text/html as safe text/plain