CVE-2021-3177

Q: What is the severity of CVE-2021-3177?

CVE-2021-3177 has a CVSS score of 9.8 (CRITICAL). This is a buffer overflow vulnerability in Python's ctypes module that could allow remote code execution. It affects Python applications that process untrusted floating-point numbers through ctypes. The vulnerability exists in Python 3.x through 3.9.1.

9.8 CRITICAL

Remote Code Execution Buffer Overflow

📋 TL;DR

This is a buffer overflow vulnerability in Python's ctypes module that could allow remote code execution. It affects Python applications that process untrusted floating-point numbers through ctypes. The vulnerability exists in Python 3.x through 3.9.1.

💻 Affected Systems

Products:

Python
Applications using Python ctypes module

Versions: Python 3.x through 3.9.1

Operating Systems: All operating systems running affected Python versions

Default Config Vulnerable: ⚠️ Yes

Notes: Only vulnerable when ctypes processes untrusted floating-point numbers. Many Python applications may not use this functionality.

📦 What is this software?

Active Iq Unified Manager by Netapp

View all CVEs affecting Active Iq Unified Manager →

Active Iq Unified Manager by Netapp

View all CVEs affecting Active Iq Unified Manager →

Communications Cloud Native Core Network Function Cloud Native Environment by Oracle

View all CVEs affecting Communications Cloud Native Core Network Function Cloud Native Environment →

Python by Python

Python is a high-level, interpreted programming language known for its readability and versatility. It is widely used in web development, data science, automation, and scientific computing.

Learn more about Python →

Python by Python

Python is a high-level, interpreted programming language known for its readability and versatility. It is widely used in web development, data science, automation, and scientific computing.

Learn more about Python →

Python by Python

Python is a high-level, interpreted programming language known for its readability and versatility. It is widely used in web development, data science, automation, and scientific computing.

Learn more about Python →

Python by Python

Python is a high-level, interpreted programming language known for its readability and versatility. It is widely used in web development, data science, automation, and scientific computing.

Learn more about Python →

Zfs Storage Appliance Kit by Oracle

View all CVEs affecting Zfs Storage Appliance Kit →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution with the privileges of the Python process, potentially leading to complete system compromise.

🟠

Likely Case

Application crash (denial of service) or limited code execution depending on application context and exploit sophistication.

🟢

If Mitigated

No impact if patched or if application doesn't use ctypes with untrusted floating-point input.

🌐 Internet-Facing: HIGH

🏢 Internal Only: MEDIUM

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Proof of concept demonstrates triggering the overflow with 1e300 argument. Exploitation requires specific application context.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Python 3.9.2 and later

Vendor Advisory: https://bugs.python.org/issue42938

Restart Required: Yes

Instructions:

1. Upgrade Python to version 3.9.2 or later. 2. Restart all Python applications and services. 3. For embedded systems, update Python runtime.

🔧 Temporary Workarounds

Input validation

all

Validate and sanitize floating-point inputs before passing to ctypes functions

Disable vulnerable functionality

all

Avoid using c_double.from_param with untrusted input

🧯 If You Can't Patch

Implement strict input validation for floating-point numbers in applications using ctypes
Use application firewalls or WAFs to filter suspicious floating-point inputs

🔍 How to Verify

Check if Vulnerable:

Check Python version with 'python --version' or 'python3 --version'. If version is 3.x through 3.9.1, system is vulnerable.

Check Version:

python --version

Verify Fix Applied:

After patching, verify Python version is 3.9.2 or later. Test ctypes functionality with sample applications.

📡 Detection & Monitoring

Log Indicators:

Python application crashes with segmentation faults
Unexpected process termination in Python services

Network Indicators:

Unusual network connections from Python processes
Traffic containing very large floating-point numbers

SIEM Query:

Process:python AND (EventID:1000 OR EventID:1001) OR Process:python AND (ExceptionCode:c0000005 OR ExceptionCode:c0000409)

📊 Metadata

CVE ID: CVE-2021-3177

CVSS v3 Score: 9.8 (CRITICAL)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CWE: CWE-120

Published: January 19, 2021

Last Updated: December 18, 2025

📋 TL;DR

💻 Affected Systems

📦 What is this software?

Active Iq Unified Manager by Netapp

Active Iq Unified Manager by Netapp

Communications Cloud Native Core Network Function Cloud Native Environment by Oracle

Communications Offline Mediation Controller by Oracle

Communications Pricing Design Center by Oracle

Debian Linux by Debian

Enterprise Manager Ops Center by Oracle

Fedora by Fedoraproject

Fedora by Fedoraproject

Ontap Select Deploy Administration Utility by Netapp

Python by Python

Python by Python

Python by Python

Python by Python

Zfs Storage Appliance Kit by Oracle

⚠️ Risk & Real-World Impact

Worst Case

Likely Case

If Mitigated

🎯 Exploit Status

🛠️ Fix & Mitigation

✅ Official Fix

Instructions:

🔧 Temporary Workarounds

Input validation

Disable vulnerable functionality

🧯 If You Can't Patch

🔍 How to Verify

Check if Vulnerable:

Check Version:

Verify Fix Applied:

📡 Detection & Monitoring

Log Indicators:

Network Indicators:

SIEM Query:

📊 Metadata

🔗 References

📤 Share & Export

🔗 Related Vulnerabilities