# CVE-2026-126207: Loofah: CSS url() sanitization bypass via escaped parentheses

> Attackers can bypass Loofah's CSS url() sanitization with escaped parentheses to make viewers' browsers request attacker-chosen URLs, leaking IP and user agent data.

- **Severity:** Medium 4.7 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Harmful if only installed:** No
- **Needs a specific call:** No
- **Fix available:** Yes
- **Published:** 12 Nov 2026
- **Updated:** 12 Nov 2026
- **Also known as:** GHSA-m3x9-938q-5767

## What is CVE-2026-126207?

CVE-2026-126207 is a medium-severity security feature bypass vulnerability in flavorjones loofah, published on 12 Nov 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

Loofah is a general library for manipulating and transforming HTML/XML documents and fragments, built on top of Nokogiri. Prior to 2.25.3, Loofah::HTML5::Scrub.scrub_css checks only the first parse of a style attribute, then rebuilds CSS with identifier escapes decoded so escaped parentheses, property names, comments, or quotes can become a live url() without a second safety check. An attacker can use list-style to make a viewer's browser request an attacker-chosen URL when content renders, or cursor to make the request on hover. The request can disclose the viewer's IP address, user agent, access timing, and access to internal-network hosts, but no script survives sanitization and the attacker cannot read the response. This issue is fixed in version 2.25.3.

Weakness: CWE-184 (Incomplete List of Disallowed Inputs), CWE-180 (Incorrect Behavior Order: Validate Before Canonicalize)

## Which versions are affected by CVE-2026-126207?

1 open source package ship an affected version, including loofah.

An affected version is exposed as installed. No special setting or call is needed.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `loofah` | RubyGems | All versions | 2.25.3 |

## How do I fix CVE-2026-126207?

Upgrade loofah to 2.25.3 or later.

## Is CVE-2026-126207 being exploited?

There is no known exploitation of CVE-2026-126207 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-126207 and fix it if it is affected.

What it is: CVE-2026-126207 is a medium-severity security feature bypass vulnerability in flavorjones loofah, published on 12 Nov 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-126207 in the wild and no public exploit code.
Exposure: An affected version is exposed as installed. No special setting or call is needed.

Affected packages and fixed versions:
- loofah (RubyGems): affected all versions; fixed in 2.25.3

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-126207/ (Markdown: https://insights.sbomify.com/CVE-2026-126207/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-126207
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-126207
- OSV: https://osv.dev/vulnerability/CVE-2026-126207

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-126207/
Summaries are generated and may contain mistakes; the official description above is the record.