CVE-2021-33503 : Security Advisory and Response

An in-depth look at CVE-2021-33503 highlighting the vulnerability discovered in urllib3 before version 1.26.5 that could lead to a denial of service attack.

Understanding CVE-2021-33503

CVE-2021-33503 is a vulnerability found in urllib3, pre-version 1.26.5, that can be exploited by a specially crafted URL to cause denial of service.

What is CVE-2021-33503?

The issue in urllib3 arises when the authority part of a URL contains multiple @ characters, triggering excessive backtracking in the regular expression used for validation. This vulnerability could be abused to launch denial of service attacks when a malicious URL is passed as a parameter or accessed via an HTTP redirect.

The Impact of CVE-2021-33503

The exploitation of this vulnerability could result in a denial of service condition, causing significant disruption to affected systems and services. Attackers could potentially use this weakness to render services inaccessible.

Technical Details of CVE-2021-33503

Here are the technical specifics of the CVE-2021-33503 vulnerability:

Vulnerability Description

The vulnerability in urllib3, before version 1.26.5, results from catastrophic backtracking in the regular expression used to parse URLs with many @ characters in the authority component.

Affected Systems and Versions

All versions of urllib3 prior to 1.26.5 are affected by this vulnerability. Systems that utilize urllib3 for URL handling are at risk.

Exploitation Mechanism

By exploiting the flawed regular expression related to parsing URLs with multiple @ characters in the authority section, attackers can induce a denial of service condition.

Mitigation and Prevention

Taking immediate actions and implementing long-term security practices are crucial in mitigating the risks associated with CVE-2021-33503.

Immediate Steps to Take

Update urllib3 to version 1.26.5 or later to eliminate the vulnerability.
Monitor network traffic for any signs of malicious activity targeting this vulnerability.

Long-Term Security Practices

Regularly update and patch software to ensure known vulnerabilities are addressed promptly.
Implement network security measures to detect and prevent denial of service attacks.

Patching and Updates

Stay informed about security advisories and updates related to urllib3 to deploy patches promptly and secure your systems from potential threats.