Fickling check_safety() bypass: dotted __qualname__ in STACK_GLOBAL resolves a class-method attribute path that evades call analysis
Summary
| CVE | CVE-2026-118938 |
|---|---|
| State | PUBLISHED |
| Assigner | BombadilSystems |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-10-30 22:16:54 UTC |
| Updated | 2026-10-30 22:16:54 UTC |
| Description | In Trail of Bits fickling through 0.1.12, a pickle STACK_GLOBAL operand carrying a dotted __qualname__ (for example "Values.read_file") is resolved by pickle's find_class through _getattribute to an arbitrary attribute path rather than to a module-level function. Fickling records only the leading component of the name in its import tracking and renders the operation as a plain import (for instance, 'python -m fickling' displays it as 'from optparse import Values.read_file'), so the trailing attribute reference is never analyzed as a call. The OvertlyBadEvals analysis pass does not flag it, and check_safety() returns LIKELY_SAFE with zero findings. This allows an attacker to reach a class method that performs code execution: optparse.Values.read_file executes exec(open(filename).read(), vars), achieving arbitrary code execution when the crafted pickle is loaded through fickling.load(), which chains check_safety() into pickle.loads() as an explicit security gate. optparse is present in all current CPython 3.x releases (deprecated as of Python 3.13, not removed). This weakness is in the resolution and analysis of dotted attribute-path names, and is distinct from and independently fixable from the module-origin trust weakness tracked as CVE-2026-16760: resolving or flagging dotted attribute-path imports closes this vector while leaving the module-level trust behavior unchanged. This bypass was verified to remain present on the vendor master branch at commit d011709 as of 2026-10-30, after the vendor's October blocklist additions and a new heuristic that flags private stdlib attributes; because the public class method Values.read_file is neither blocklisted nor flagged as a private attribute, it is not addressed by those remediations. |
Risk And Classification
Primary CVSS: v3.1 8.8 HIGH from aa17e1a1-c329-4d6e-a1ed-8d0188aea082
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Problem Types: CWE-502 | CWE-706 | CWE-706 CWE-706 Use of Incorrectly-Resolved Name or Reference | CWE-502 CWE-502 Deserialization of Untrusted Data
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 3.1 | aa17e1a1-c329-4d6e-a1ed-8d0188aea082 | Secondary | 8.8 | HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H |
| 3.1 | CNA | CVSS | 8.8 | HIGH | CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H |
CVSS v3.1 Breakdown
Attack Vector
NetworkAttack Complexity
LowPrivileges Required
NoneUser Interaction
RequiredScope
UnchangedConfidentiality
HighIntegrity
HighAvailability
HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Trailofbits | Fickling | affected 0.1.12 custom | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| github.com/trailofbits/fickling | aa17e1a1-c329-4d6e-a1ed-8d0188aea082 | github.com | |
| github.com/trailofbits/fickling/commit/d011709 | aa17e1a1-c329-4d6e-a1ed-8d0188aea082 | github.com | |
| bombadil.systems/advisories.html | aa17e1a1-c329-4d6e-a1ed-8d0188aea082 | bombadil.systems | |
| pypi.org/project/fickling/0.1.12 | aa17e1a1-c329-4d6e-a1ed-8d0188aea082 | pypi.org | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: Christopher Aziz (Bombadil Systems LLC) (en)
There are currently no legacy QID mappings associated with this CVE.