{"uuid": "d509770d-78c0-4e52-b7c1-15bc9b9886e0", "vulnerability_lookup_origin": "1a89b78e-f703-45f3-bb86-59eb712668bd", "author": "9f56dd64-161d-43a6-b9c3-555944290a09", "vulnerability": "GHSA-gj48-438w-jh9v", "type": "seen", "source": "https://gist.github.com/alon710/ca91eafc27ab49b122bd87e653053fb2", "content": "# GHSA-GJ48-438W-JH9V: GHSA-GJ48-438W-JH9V: Client-Side HTML Sanitization Bypass in Bleach\n\n> **CVSS Score:** 6.1\n> **Published:** 2026-06-16\n> **Full Report:** https://cvereports.com/reports/GHSA-GJ48-438W-JH9V\n\n## Summary\nA client-side HTML sanitization bypass vulnerability exists in the Bleach library where the formaction attribute is not recognized as a URI. This allows attackers to inject javascript: URIs when formaction is on the allowed list, resulting in Cross-Site Scripting (XSS).\n\n## TL;DR\nBleach fails to sanitize the formaction attribute, permitting submit-triggered XSS when explicitly allowed in configurations.\n\n## Exploit Status: POC\n\n## Technical Details\n\n- **CWE ID**: CWE-79\n- **Attack Vector**: Network (AV:N)\n- **CVSS Score**: 6.1\n- **Impact**: Client-Side Code Execution (XSS)\n- **Exploit Status**: PoC\n- **KEV Status**: Not Listed\n\n## Affected Systems\n\n- Bleach (PyPI Package)\n- **bleach**: < 6.4.0 (Fixed in: `6.4.0`)\n\n## Mitigation\n\n- Upgrade Bleach to version 6.4.0 or newer.\n- Do not explicitly allow the formaction attribute in configurations.\n- Migrate to supported HTML sanitizers such as nh3.\n\n**Remediation Steps:**\n1. Identify all occurrences of bleach.clean() and bleach.Cleaner() in the codebase.\n2. Audit custom whitelists to ensure the formaction attribute is not permitted.\n3. Execute pip install --upgrade bleach to update the package to 6.4.0.\n4. Evaluate and implement migration of the codebase to nh3 or another actively maintained sanitization library.\n\n## References\n\n- [Official GitHub Security Advisory](https://github.com/mozilla/bleach/security/advisories/GHSA-gj48-438w-jh9v)\n- [Mozilla Bleach GitHub Repository](https://github.com/mozilla/bleach)\n- [Mozilla Bleach v6.4.0 Release Page](https://github.com/mozilla/bleach/releases/tag/v6.4.0)\n- [Mozilla Bleach Deprecation Statement](https://github.com/mozilla/bleach/issues/698)\n- [GitHub Advisory Database Catalog Link](https://github.com/advisories/GHSA-gj48-438w-jh9v)\n\n\n---\n*Generated by [CVEReports](https://cvereports.com/reports/GHSA-GJ48-438W-JH9V) - Automated Vulnerability Intelligence*", "creation_timestamp": "2026-06-16T14:41:17.000000Z"}