[bacescuandrei]

Description

BaseKnowledgeService._update_fact() only applies an update when the current attribute value is truthy:

if getattr(match, k, False):
    setattr(match, k, v)

So knowledge_svc.update_fact() and PATCH /api/v2/facts silently ignore updates to fields whose current value is 0, None, '' or []. Examples are a fact with score 0, technique_id None, or an empty source. Operation.all_facts() only returns facts with score > 0, so a fact whose score dropped to 0 can never be given a positive score again.

This change checks that the attribute exists (hasattr), as _update_relationship() already does.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

• Added test_update_fact_with_falsy_current_value to tests/services/test_knowledge_svc.py. It updates score from 0 and technique_id from None, and checks that an unknown key is not added.
• The test fails on master (assert 0 == 2) and passes with the change.
• Full suite on Python 3.12: 562 passed, 1 xfailed.
• flake8 and bandit are clean on the changed files.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have added tests that prove my fix is effective or that my feature works