CVE-2021-3177 is a critical buffer overflow vulnerability found in Python versions 3.x through 3.9.1. The flaw exists in the function PyCArg_repr in the _ctypes/callproc.c file, where unsafe usage of sprintf can be exploited. Specifically, it allows for remote code execution in Python applications that accept floating-point numbers as untrusted input. An example of this exploitation is demonstrated by passing a 1e300 argument to c_double.from_param.
The CVSS score for this vulnerability is 9.8, classifying it as critical. The attack vector is network-based, with low complexity and no privileges or user interaction required. The potential impacts include high confidentiality, integrity, and availability risks, making this a significant concern for organizations.
Given its severity, organizations using affected Python versions must prioritize patching and remediation efforts immediately to prevent exploitation.
The vulnerability was published on January 19, 2021, and has been modified in the CVE database as of December 18, 2025. It affects multiple vendors, including Debian, Fedora, NetApp, Oracle, and the Python Software Foundation.
Organizations must take proactive measures to ensure their systems are not vulnerable to such critical threats.
Vulnerability Details
Python 3.x through 3.9.1 has a buffer overflow in PyCArg_repr in _ctypes/callproc.c, which may lead to remote code execution in certain Python applications that accept floating-point numbers as untrusted input, as demonstrated by a 1e300 argument to c_double.from_param. This occurs because sprintf is used unsafely.
The CVSS score is 9.8, indicating a critical severity. The vulnerability affects Python and its associated applications. The vulnerability was disclosed on January 19, 2021.
Technical Analysis
The root cause of the vulnerability stems from improper handling of floating-point numbers in Python's C API. Specifically, the unsafe use of sprintf leads to buffer overflow conditions that attackers can exploit. The attack vector is network-based, allowing attackers to send crafted floating-point numbers to vulnerable applications. The complexity of the attack is low, and no privileges or user interaction are required, making it easily exploitable.
The confidentiality, integrity, and availability impacts of this vulnerability are all rated as high, given the potential for remote code execution and the ability to manipulate or disrupt services.
Risk & Impact Analysis
Organizations utilizing affected Python versions face significant risks, including the potential for unauthorized remote code execution. The vulnerability can be exploited by sending specially crafted inputs, allowing an attacker to execute arbitrary code in the context of the affected application. This could result in data breaches, service interruptions, or further compromise of the organization's IT infrastructure.
The urgency for organizations to address this vulnerability is critical due to its high CVSS score and the potential for widespread impact across various applications relying on affected Python versions. Organizations should prioritize the deployment of patches and immediate remediation.
Exploitation Status
Signal | Status |
|---|---|
Known Exploit | No |
Public PoC | No |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
The vulnerability affects Python versions 3.6.0 to 3.9.1. Additionally, several operating systems and applications are vulnerable, including Fedora versions 32 and 33, Debian Linux version 9.0, and various products from NetApp and Oracle.
Mitigation & Remediation
Organizations should prioritize patching immediately. The latest Python version should be deployed to remediate this vulnerability. For those unable to apply the patch immediately, configuration hardening practices should be implemented to restrict untrusted input.
The long-term significance of CVE-2021-3177 lies in its demonstration of how critical vulnerabilities in widely-used programming languages can have a profound impact. This incident underscores the necessity for security teams to adopt proactive measures in vulnerability management and to prioritize the timely application of patches. For comprehensive insights into vulnerability management, refer to our vulnerability management program and the importance of regular security assessments, such as penetration testing methodology to identify and mitigate similar vulnerabilities.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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