CVE-2025-66418
urllib3 allows an unbounded number of links in the decompression chain
Description
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.
INFO
Published Date :
Dec. 5, 2025, 4:15 p.m.
Last Modified :
Dec. 10, 2025, 4:08 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | HIGH | [email protected] | ||||
| CVSS 4.0 | HIGH | [email protected] |
Solution
- Update urllib3 to version 2.6.0 or newer.
- Monitor system resource usage after update.
Public PoC/Exploit Available at Github
CVE-2025-66418 has a 2 public
PoC/Exploit available at Github.
Go to the Public Exploits tab to see the list.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2025-66418.
| URL | Resource |
|---|---|
| https://github.com/urllib3/urllib3/commit/24d7b67eac89f94e11003424bcf0d8f7b72222a8 | Patch |
| https://github.com/urllib3/urllib3/security/advisories/GHSA-gm62-xv2j-4w53 | Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2025-66418 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2025-66418
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
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Shell Python Nix Dockerfile
None
Python HTML Dockerfile JavaScript CSS TypeScript Shell PLpgSQL
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2025-66418 vulnerability anywhere in the article.
-
Daily CyberSecurity
urllib3 Flaws Risk Client DoS via Unbounded Decompression and Streaming Resource Exhaustion
The maintainers of urllib3, the ubiquitous HTTP client for Python, have issued a security advisory detailing two high-severity vulnerabilities that could allow malicious servers to crash client applic ... Read more
The following table lists the changes that have been made to the
CVE-2025-66418 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Dec. 10, 2025
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Added CPE Configuration OR *cpe:2.3:a:python:urllib3:*:*:*:*:*:*:*:* versions from (including) 1.24 up to (excluding) 2.6.0 Added Reference Type GitHub, Inc.: https://github.com/urllib3/urllib3/commit/24d7b67eac89f94e11003424bcf0d8f7b72222a8 Types: Patch Added Reference Type GitHub, Inc.: https://github.com/urllib3/urllib3/security/advisories/GHSA-gm62-xv2j-4w53 Types: Vendor Advisory -
New CVE Received by [email protected]
Dec. 05, 2025
Action Type Old Value New Value Added Description 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. Added CVSS V4.0 AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Added CWE CWE-770 Added Reference https://github.com/urllib3/urllib3/commit/24d7b67eac89f94e11003424bcf0d8f7b72222a8 Added Reference https://github.com/urllib3/urllib3/security/advisories/GHSA-gm62-xv2j-4w53