CVE-2025-4517: Critical Vulnerability in Python’s Tarfile Module

Overview

The vulnerability labeled as CVE-2025-4517 is a serious security flaw found in Python’s tarfile module. This vulnerability allows potential attackers to write arbitrarily to the filesystem outside the extraction directory during the extraction process. Python developers who employ the tarfile module to extract untrusted tar archives using TarFile.extractall() or TarFile.extract() with a filter= parameter set to “data” or “tar” are at risk. This issue is particularly pressing as it could lead to system compromise or data leakage.

Vulnerability Summary

CVE ID: CVE-2025-4517
Severity: Critical – CVSS 9.4
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: System compromise or data leakage

Affected Products

Product | Affected Versions

Python | 3.14 or later

How the Exploit Works

The exploit takes advantage of a flaw in Python’s tarfile module during the extraction process. If untrusted tar archives are extracted using TarFile.extractall() or TarFile.extract() with a filter= parameter set to “data” or “tar”, the attacker’s arbitrary code can be written to the filesystem outside the extraction directory. This could enable the attacker to execute malicious code, compromise the system, or lead to potential data leakage.

Conceptual Example Code

Let’s consider a conceptual example where the attacker sends a malicious tar file to the victim. If the victim uses the vulnerable Python code to extract the file, the attacker’s arbitrary code can be written outside of the extraction directory. The code could look something like this:

import tarfile
# open the malicious tar file
tar = tarfile.open("malicious.tar")
# extract the tar file with filter set to "data"
tar.extractall(path="/safe/directory", filter="data")

In this instance, the attacker’s malicious code could be written to parts of the filesystem outside “/safe/directory”, potentially compromising the system or leading to data leakage.

Mitigation Guidance

Users are advised to apply the vendor patch as soon as it becomes available. In the interim, using a Web Application Firewall (WAF) or Intrusion Detection System (IDS) can offer temporary mitigation. Additionally, developers should avoid using the tarfile module to extract untrusted tar archives, and should refrain from using the filter= parameter with a value of “data” or “tar”.