CVE-2026-14534 Fickling check_safety() bypass via unlisted standard library modules (_posixsubprocess, site, atexit)
Attackers can bypass safety checks in fickling to execute arbitrary code via malicious pickle payloads using unlisted standard library modules.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-14534?
CVE-2026-14534 is a high-severity unsafe deserialization vulnerability in trailofbits fickling, published on 4 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
Trail of Bits fickling versions up to and including 0.1.10 do not include the Python standard library modules _posixsubprocess, site, and atexit in the UNSAFE_IMPORTS denylist (fickle.py). Because these modules are absent from the denylist, fickling's check_safety() function returns LIKELY_SAFE with zero findings for pickle payloads that invoke dangerous functions including _posixsubprocess.fork_exec (C-level process spawner capable of executing arbitrary binaries), site.execsitecustomize (executes arbitrary site customization code), and atexit._run_exitfuncs (triggers all registered exit handler callbacks). The fickling.load() API chains check_safety() into pickle.loads() as an explicit security gate; a LIKELY_SAFE verdict causes the payload to be deserialized and executed. This shares the same root cause as CVE-2026-22607 (cProfile), CVE-2025-67748 (pty), and CVE-2025-67747 (marshal/types). OvertlyBadEvals does not flag these modules because they are standard library imports. UnsafeImports does not flag them because they are not in the denylist. The UnusedVariables heuristic is defeated by the SETITEMS opcode pattern.
Which versions are affected by CVE-2026-14534?
1 open source package ship an affected version, including fickling. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
fickling PyPI | All versions | 0.1.11 |
Products include Trailofbits Fickling.
How do I fix CVE-2026-14534?
Upgrade fickling to 0.1.11 or later.
Upgrade, and only deserialise data from trusted sources or with an allow-list of types. More about Unsafe deserialization.
Is CVE-2026-14534 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-14534 exists.
Other vulnerabilities in trailofbits fickling
- CVE-2026-22606 Fickling has a bypass via runpy.run_path() and runpy.run_module()
- CVE-2026-22607 Fickling Blocklist Bypass: cProfile.run()
- CVE-2026-22608 Fickling vulnerable to use of ctypes and pydoc gadget chain to bypass detection
- CVE-2026-22609 Fickling has Static Analysis Bypass via Incomplete Dangerous Module Blocklist
- CVE-2026-22612 Fickling vulnerable to detection bypass due to "builtins" blindness
Sources
Also known as GHSA-m6fh-58r7-x697, GHSA-v8cr-9jrc-fwf9, PYSEC-2026-2149.