CVE-2025-66418

A flaw was found in urllib3 Python library that could lead to a Denial of Service condition. A remote, malicious server can exploit this flaw by responding to a client request with an HTTP message that uses an excessive number of chained compression algorithms. This unlimited decompression chain causes the client system to consume a virtually unbounded amount of CPU resources and memory. The high resource usage leads to service disruption, making the application unresponsive.

This Important impact denial of service vulnerability in the urllib3 HTTP client library allows uncontrolled memory consumption when decompressing highly compressed HTTP responses. Due to the lack of an overall decompression size limit in the Streaming API, a malicious server can exhaust client memory, leading to a denial of service.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.