CVSS 4.0
5.3 mediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:NCVE-2026-126209
Loofah allowed_uri? treats javascript: alert(1) as safe
Medium (5.3) in flavorjones loofah. Fixed in loofah 2.25.3.
On this page
Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. From 2.25.0 until 2.25.3, Loofah::HTML5::Scrub.allowed_uri? strips whitespace and control characters before decoding a semicolon-less numeric character reference, changing where the reference ends and hiding a javascript: or vbscript: scheme that a browser reconstructs. The bypass applies to encoded colons and encoded scheme letters when a stripped character terminates the numeric reference. An application that renders the approved value in href or another browser-interpreted URI attribute can allow cross-site scripting, and Rails::HTML::Sanitizer.allowed_uri? re-exports the affected helper. Loofah's default sanitize() path is not affected because Nokogiri decodes entities before URI evaluation. This issue is fixed in version 2.25.3.
Severity
- CWEs
- CWE-79 Improper Neutralization of Input During Web Page Generation (Cross-site Scripting)
CWE-184 Incomplete List of Disallowed Inputs - OWASP Top 10
- A05:2025 Injection
- Published
- Modified
- Assigned by
- GitHub_M (CNA)
- NVD analysis
- Awaiting analysis
- Record from
- the NVD, synced
Ask an AI about this CVE
Show the prompt
Explain CVE-2026-126209 for an engineer deciding whether to act. Use https://cve.bz/api/public/cves/CVE-2026-126209?via=ask-ai-copy and https://cve.bz/cve/CVE-2026-126209?via=ask-ai-copy as the source of truth: what is affected and which versions fix it, whether it is in CISA KEV, public exploits, and its EPSS (an internet-wide 30-day estimate of exploitation activity, not a forecast for my systems). If they give no fixed versions, use the CVE record https://cveawg.mitre.org/api/cve/CVE-2026-126209 or the vendor advisory, not third-party mirrors. Tell me how to check whether I am affected and how to verify a fix. Cite the sources and say where they are uncertain.Opens a third-party assistant; its answer is its own, not cve.bz's. The prompt holds only this CVE's id and public links.
Badge for a README or a site
An image that stays current: it is drawn from the data each time it is fetched (a host that proxies images, as GitHub does, may show its copy for a while). Markdown:
[](https://cve.bz/cve/CVE-2026-126209)
HTML:
<a href="https://cve.bz/cve/CVE-2026-126209"><img src="https://cve.bz/cve/badge/CVE-2026-126209.svg" alt="CVE-2026-126209"></a>
Affected
Versions
From the CNA's record in the CVE List.
| Product | Affected |
|---|---|
| flavorjones loofah | >= 2.25.0, < 2.25.3 |
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-p9wj-w8xq-vjx6 | RubyGems | loofah | >=2.25.0 <2.25.3 | 2.25.3 |
Attack patterns (CAPEC)
- CAPEC-63 Cross-Site Scripting (XSS) Likelihood: High · Severity: Very High
- CAPEC-85 AJAX Footprinting Likelihood: High · Severity: Low
- CAPEC-209 XSS Using MIME Type Mismatch Severity: Medium
- CAPEC-588 DOM-Based XSS Likelihood: High · Severity: Very High
- CAPEC-591 Reflected XSS Likelihood: High · Severity: Very High
- CAPEC-592 Stored XSS Likelihood: High · Severity: Very High
- CAPEC-3 Using Leading 'Ghost' Character Sequences to Bypass Input Filters Likelihood: Medium · Severity: Medium
- CAPEC-6 Argument Injection Likelihood: High · Severity: High
- CAPEC-15 Command Delimiters Likelihood: High · Severity: High
- CAPEC-43 Exploiting Multiple Input Interpretation Layers Likelihood: Medium · Severity: High
The attack patterns MITRE's CAPEC relates to this record's weaknesses, as MITRE names them. Credits. More on the page of CWE-184.