The vulnerability is caused by PyFory's ReduceSerializer bypassing DeserializationPolicy validation hooks during reduce‑state restoration and global‑name resolution when strict mode is disabled. As a result, an attacker can craft serialized objects that will be deserialized without policy enforcement, enabling execution of arbitrary code. This is a classic insecure deserialization flaw.

All Apache Fory releases before version 1.0.0 are affected; any application that uses PyFory in Python‑native mode with strict mode turned off and relies on DeserializationPolicy to limit unsafe classes or functions is vulnerable.

The CVSS score of 9.8 marks the issue as critical. EPSS data are not available, so the current probability of exploitation cannot be quantified, and the vulnerability has not yet been listed in CISA KEV. The likely attack path entails an attacker delivering a maliciously crafted serialized payload to a Python application that loads it with PyFory in native mode, bypassing policy checks and achieving remote code execution. This inference is based on the description of the deserialization bypass and the requirement for attacker‑controlled data to trigger the flaw.