Detect local subclasses of Markup in B704

[ChihebBENCHEIKH1]

Summary

B704 (markupsafe_markup_xss) only reports a call when the resolved name of the callee is one of the recognized Markup classes: markupsafe.Markup, flask.Markup, or a name listed under extend_markup_names. When a project defines its own subclass of Markup and passes dynamic data to it, the call is not reported. This is the false negative described in #1405 and tied to CVE-2025-54384.

Reproduction

from markupsafe import Markup


class Lit(Markup):
    pass


content = input()
Lit(f"unsafe {content}")   # not reported before this change

Before: only direct Markup(...) calls are reported.
After: calls to a local subclass of a Markup class are reported as well.

What changed

• BanditNodeVisitor now records the resolved base classes of every class definition it walks, alongside the existing import tracking, and exposes them on the context as context.classes.
• B704 walks that inheritance graph and treats a call to a local class that subclasses a Markup class, directly or through a chain of subclasses, the same way it treats a direct Markup call. Subclasses of a configured extend_markup_names entry are covered too.
• The two example files gain direct, nested, and configured-name subclass cases, and the functional test counts are updated. A call with a constant argument stays unreported, so no false positives are introduced.

Testing

• stestr run (full suite): 273 passing
• flake8 bandit tests: clean
• black, reorder-python-imports, pyupgrade: no changes
• bandit -r bandit -ll -ii: no new findings

Resolves #1405