Summary
PraisonAI Vulnerable to Stored XSS via Unsanitized Agent Output in HTML Rendering (nh3 Not a Required Dependency)
Impact
- Session hijacking: An attacker can steal cookies or session tokens from users viewing the API output.
- Credential theft: Injected scripts can present fake login forms or exfiltrate data to attacker-controlled servers.
- Actions on behalf of users: Malicious JavaScript can perform actions in the context of the victim's browser session.
The attack surface includes any scenario where agent output contains attacker-influenced content: RAG retrieval from poisoned documents, web scraping of malicious pages, processing of adversarial user prompts, or multi-agent communication where one agent's output is tainted.
Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.
CVE-2026-40112 has a CVSS score of 5.4 (Medium). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.5.128); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
Make nh3 a required dependency when using the API, and remove the silent fallback:
# Option 1: Make nh3 required in pyproject.toml under the "api" optional dependency
# In pyproject.toml:
# api = [
# "flask>=3.0.0",
# ...
# "nh3>=0.2.14",
# ]
# Option 2: Use markdown's built-in HTML stripping as a safe default
import markdown
def _sanitize_html(html: str) -> str:
try:
import nh3
return nh3.clean(html)
except ImportError:
import re
return re.sub(r'<[^>]+>', '', html) # Strip all HTML tags as fallback
# Option 3 (preferred): Use Flask's Jinja2 templating with auto-escaping
# instead of f-string interpolation, or use markupsafe.escape()
from markupsafe import Markup
@app.route('/')
def home():
output = basic()
# Use markdown with safe extensions only
html_output = markdown.markdown(str(output), extensions=[])
try:
import nh3
html_output = nh3.clean(html_output)
except ImportError:
raise RuntimeError("nh3 is required for safe HTML rendering. Install with: pip install nh3")
return f'<html><body>{html_output}</body></html>'
Also fix deploy.py:76-91 to include sanitization in the generated api.py.
Frequently Asked Questions
- What is CVE-2026-40112? CVE-2026-40112 is a medium-severity cross-site scripting (XSS) vulnerability in PraisonAI (pip), affecting versions < 4.5.128. It is fixed in 4.5.128. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
- How severe is CVE-2026-40112? CVE-2026-40112 has a CVSS score of 5.4 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of PraisonAI are affected by CVE-2026-40112? PraisonAI (pip) versions < 4.5.128 is affected.
- Is there a fix for CVE-2026-40112? Yes. CVE-2026-40112 is fixed in 4.5.128. Upgrade to this version or later.
- Is CVE-2026-40112 exploitable, and should I be worried? Whether CVE-2026-40112 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-40112 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-40112? Upgrade
PraisonAIto 4.5.128 or later.