CVE-2025-61622: Remote Code Execution Vulnerability in Python’s Pyfory and Pyfury Libraries

Overview

The vulnerability tracked as CVE-2025-61622 is a critical flaw that resides in the Pyfory library of Python, versions 0.12.0 through 0.12.2, and its predecessor Pyfury, versions from 0.1.0 through 0.10.3. This vulnerability, if exploited, could enable an attacker to execute arbitrary code on the affected system. It is of utmost importance due to its high severity score and the potential for widespread impact, affecting any application that reads Pyfory serialized data from untrusted sources.

Vulnerability Summary

CVE ID: CVE-2025-61622
Severity: Critical (CVSS: 9.8)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Potential system compromise and data leakage

Affected Products

Product | Affected Versions

Python Pyfory | 0.12.0 – 0.12.2
Python Pyfury | 0.1.0 – 0.10.3

How the Exploit Works

The vulnerability stems from the deserialization of untrusted data in Python’s Pyfory and Pyfury libraries. An attacker can craft a data stream that triggers the pickle-fallback serializer during deserialization. The execution of `pickle.loads` is vulnerable to remote code execution, allowing the attacker to run arbitrary code on the system.

Conceptual Example Code

Here is a conceptual example of how an attacker could exploit this vulnerability. This pseudocode demonstrates the crafting of a malicious payload that triggers the pickle-fallback serializer:

import pickle
import os
class Exploit(object):
def __reduce__(self):
return (os.system, ('your malicious command here',))
malicious_payload = pickle.dumps(Exploit())

In this example, the `Exploit` class contains a `__reduce__` method that returns a tuple. The first element of the tuple is a callable (os.system), and the second is a tuple containing the arguments for the callable. When this object is unpickled, it will execute `os.system(‘your malicious command here’)`.
This payload could then be sent to an application using the vulnerable versions of the Pyfory or Pyfury libraries. If the application deserializes the payload, it will trigger the execution of the malicious command.

Mitigation Guidance

Users are strongly recommended to upgrade to Pyfory version 0.12.3 or later, which has removed the pickle fallback serializer and thus fixes this issue. In cases where immediate patching is not possible, employing Web Application Firewalls (WAF) or Intrusion Detection Systems (IDS) could provide temporary mitigation. However, these should not be considered as long-term solutions, as they may not fully protect against exploits targeting this vulnerability.