The recent release of PickleScan version ..22 comes with a significant security improvement. As the number of data manipulation and storage applications utilizing the Python Pickle serialization library grows, ensuring proper security measures in place is increasingly important. Alongside this growth, the discovery of CVE-2025-1889 highlights a previously overlooked area of risk regarding the use of non-standard pickle file extensions in versions of PickleScan prior to ..22.

In the case of CVE-2025-1889, an attacker could exploit the vulnerability by crafting a malicious model that uses Pickle and includes a malicious pickle file with a non-standard file extension. Due to the limitations of previous versions of PickleScan, the malicious file would pass security checks and appear to be safe.

In this post, we will break down this vulnerability, analyze how it can be exploited, and provide code snippets to illustrate the process. We will also share details on how to mitigate this risk by updating your installation of PickleScan.

Exploit Details

In vulnerable versions of PickleScan (before ..22), only standard pickle file extensions are considered within the scope of its security scanning process. As a result, an attacker could craft a malicious model that utilizes the Pickle serialization library and include a malicious pickle file with a non-standard file extension (e.g., ".pklz" or ".badpkl"). This malicious file would be overlooked during the security check, allowing the attacker to successfully compromise a system that relies on PickleScan for vulnerability detection.

To demonstrate, let's walk through an example of how an attacker could exploit CVE-2025-1889 using a malicious pickle file.

An attacker would first create a malicious pickle file by defining a malicious class that performs some harmful action and then serializing it into a non-standard pickle file extension. Here's a basic example:

import os
import pickle

class MaliciousClass:
    def __init__(self):
        self.malicious_code = "rm -rf /"

    def execute(self):
        os.system(self.malicious_code)

malicious_object = MaliciousClass()
with open("malicious.pklz", "wb") as malicious_file:
    pickle.dump(malicious_object, malicious_file)

With the malicious pickle file in place, suppose a user relies on a vulnerable version of PickleScan to evaluate the security of files within a directory. The sample code for picklescan might look like this:

# Vulnerable picklescan version
import os
import pickle

def scan_for_vulnerabilities(directory):
    safe_files = []
    for file in os.listdir(directory):
        if file.endswith(".pkl"):
            with open(file, "rb") as pickle_file:
                try:
                    safe_object = pickle.load(pickle_file)
                    safe_files.append(file)
                except Exception:
                    print(f"Potential vulnerability found in {file}")
        else:
            safe_files.append(file)
    return safe_files

safe_files = scan_for_vulnerabilities(".")

Notice that since only files with the ".pkl" extension will get checked, the malicious file ("malicious.pklz") would avoid detection altogether.

Mitigating the Vulnerability

To address CVE-2025-1889, users should update their installation of PickleScan to version ..22 or later. Doing so will ensure that all pickle files, regardless of their extensions, are assessed for potential vulnerabilities. Here's a sample of how to perform picklescan in the updated version:

# Secure picklescan version
def scan_for_vulnerabilities(directory):
    safe_files = []
    for file in os.listdir(directory):
        with open(file, "rb") as pickle_file:
            try:
                safe_object = pickle.load(pickle_file)
                safe_files.append(file)
            except Exception:
                print(f"Potential vulnerability found in {file}")
    return safe_files

safe_files = scan_for_vulnerabilities(".")

CVE-2025-1889 highlights a now-patched vulnerability in PickleScan that could have allowed attackers to sneak malicious Pickle files with non-standard extensions past security checks. While the risk may have been present in versions prior to ..22, updating to the latest version ensures comprehensive scanning coverage and ongoing protection.

For more information on this vulnerability and the related patch, please refer to the following sources:

1. CVE-2025-1889 Entry
2. GitHub: PickleScan Security Advisory

As always, stay vigilant and make sure to keep your tools up-to-date to protect against evolving threats and vulnerabilities.

Timeline

Published on: 03/03/2025 19:15:34 UTC
Last modified on: 03/05/2025 20:49:16 UTC