CVE-2026-48207

Vulnerability

Overview CVE-2026-48207 is a critical deserialization vulnerability in Apache Fory's PyFory component. The ReduceSerializer fails to enforce the documented DeserializationPolicy validation hooks during reduce-state restoration and global-name resolution. This allows an attacker to bypass security restrictions that are intended to block unsafe classes, functions, or module attributes during deserialization [1].

Exploitation

Conditions Exploitation requires the application to deserialize attacker-controlled data using PyFory's Python-native mode with strict=False (strict mode disabled). The application must also rely on a custom DeserializationPolicy to restrict unsafe elements. When these conditions are met, the ReduceSerializer does not invoke the policy validation for the specific code paths, allowing an attacker to craft malicious serialized data that can lead to arbitrary class instantiation or function calls [1].

Impact and

Mitigation A successful exploit could lead to arbitrary code execution, data corruption, or other severe impacts depending on the application context. Apache has released version 1.0.0 of PyFory which consistently enforces DeserializationPolicy validation for the affected paths. Users are strongly advised to upgrade to 1.0.0 or later [1]. Additionally, note that a related but separate vulnerability (CVE-2025-61622) in older versions (0.5.0 through 0.12.2) allowed RCE via an unguarded pickle fallback serializer, which was patched in version 0.12.3 [1].