Answer in brief
CVE-2025-66418 records a High severity (CVSS 8.9) vulnerability in urllib3 allows an unbounded number of links in the decompression chain. The current sources do not mark it as known exploited. The current feed maps urllib3/urllib3 (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 8.9. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps urllib3/urllib3 (generic). Check affected ranges and fixed versions before updating.
| Product | Affected versions | Fixed versions |
|---|---|---|
| cpe:2.3:a:python:urllib3:*:*:*:*:*:*:*:* | Not reported | Not reported |
| Package | Affected range | Fixed version |
|---|---|---|
| urllib3/urllib3generic | >=1.24 <2.6.0 | 2.6.0 |
Published upstream
Dec 5, 2025
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Nov 10, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Oct 1, 2026
urllib3 is a user-friendly HTTP client library for Python. Starting in version 1.24 and prior to 2.6.0, the number of links in the decompression chain was unbounded allowing a malicious server to insert a virtually unlimited number of compression steps leading to high CPU usage and massive memory allocation for the decompressed data. This vulnerability is fixed in 2.6.0.
Quoted source text, attributed separately from HOL analysis.