--- id: CVE-2026-40112 aliases: - GHSA-cfg2-mxfj-j6pw - PYSEC-2026-2910 title: >- PraisonAI Vulnerable to Stored XSS via Unsanitized Agent Output in HTML Rendering (nh3 Not a Required Dependency) summary: >- PraisonAI Vulnerable to Stored XSS via Unsanitized Agent Output in HTML Rendering (nh3 Not a Required Dependency) severity: medium cvss: 5.4 cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N' vendor: praisonai product: praisonai ecosystem: pip affected: - praisonai < 4.5.128 patched: - praisonai 4.5.128 published: '2026-04-10' updated: '2026-07-13' source: OSV sourceUrl: 'https://osv.dev/vulnerability/GHSA-cfg2-mxfj-j6pw' references: - url: >- https://github.com/MervinPraison/PraisonAI/security/advisories/GHSA-cfg2-mxfj-j6pw - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-40112' - url: 'https://github.com/MervinPraison/PraisonAI' - url: 'https://github.com/MervinPraison/PraisonAI/releases/tag/v4.5.128' tags: - osv - pip epss: 0.00216 epssPercentile: 0.12254 ingestedAt: '2026-07-13T18:57:56.418Z' --- ## Overview ## Summary The Flask API endpoint in `src/praisonai/api.py` renders agent output as HTML without effective sanitization. The `_sanitize_html` function relies on the `nh3` library, which is not listed as a required or optional dependency in `pyproject.toml`. When `nh3` is absent (the default installation), the sanitizer is a no-op that returns HTML unchanged. An attacker who can influence agent input (via RAG data poisoning, web scraping results, or prompt injection) can inject arbitrary JavaScript that executes in the browser of anyone viewing the API output. ## Details In `src/praisonai/api.py`, lines 6-14 define the sanitizer with a try/except ImportError fallback: ```python try: import nh3 def _sanitize_html(html: str) -> str: return nh3.clean(html) except ImportError: def _sanitize_html(html: str) -> str: """Fallback: no nh3, return as-is (install nh3 for XSS protection).""" return html ``` The `home()` route at lines 21-25 converts agent output to HTML via `markdown.markdown()` (which preserves raw HTML tags by default) and embeds it in an HTML response using an f-string — bypassing Flask's Jinja2 auto-escaping: ```python @app.route('/') def home(): output = basic() html_output = _sanitize_html(markdown.markdown(str(output))) return f'{html_output}' ``` Since `nh3` is not in any dependency list (`pyproject.toml` core deps, optional deps, or requirements files), a standard installation will always hit the fallback path. The `markdown` library's default behavior passes through raw HTML tags in input text, so any `