CVE-2026-21441
urllib3 vulnerable to decompression-bomb safeguard bypass when following HTTP redirects (streaming API)
Description
urllib3 is an HTTP client library for Python. urllib3's streaming API is designed for the efficient handling of large HTTP responses by reading the content in chunks, rather than loading the entire response body into memory at once. urllib3 can perform decoding or decompression based on the HTTP `Content-Encoding` header (e.g., `gzip`, `deflate`, `br`, or `zstd`). When using the streaming API, the library decompresses only the necessary bytes, enabling partial content consumption. Starting in version 1.22 and prior to version 2.6.3, for HTTP redirect responses, the library would read the entire response body to drain the connection and decompress the content unnecessarily. This decompression occurred even before any read methods were called, and configured read limits did not restrict the amount of decompressed data. As a result, there was no safeguard against decompression bombs. A malicious server could exploit this to trigger excessive resource consumption on the client. Applications and libraries are affected when they stream content from untrusted sources by setting `preload_content=False` when they do not disable redirects. Users should upgrade to at least urllib3 v2.6.3, in which the library does not decode content of redirect responses when `preload_content=False`. If upgrading is not immediately possible, disable redirects by setting `redirect=False` for requests to untrusted source.
INFO
Published Date :
Jan. 7, 2026, 10:15 p.m.
Last Modified :
Jan. 23, 2026, 9:15 a.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
- Upgrade to urllib3 version 2.6.3 or later.
- Disable redirects if upgrading is not possible.
- Avoid streaming content from untrusted sources.
Public PoC/Exploit Available at Github
CVE-2026-21441 has a 7 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-2026-21441.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-21441 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-2026-21441
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).
None
Jupyter Notebook Python Shell Makefile Svelte JavaScript TypeScript Dockerfile HTML CSS
Secrets retrieval from the KV store of a HashiCorp Vault instance
Python Shell HCL Dockerfile
Complete audiobook management toolkit: AAX/AAXC converter (AAXtoMP3 fork v2.2), web library browser with audio player, and Docker deployment. Features Opus cover art embedding, full-text search, and multi-format support.
aax aaxc audible audiobook audiobook-library bash converter docker drm-removal ffmpeg flask m4b mp3 mutagen opus python
Dockerfile Shell Python CSS HTML JavaScript
Blueprint for Ingesting massive volumes of live or archived videos and extract insights for summarization and interactive Q&A
llm rag vlm
Jupyter Notebook Python Shell Dockerfile HTML CSS Jinja Svelte JavaScript TypeScript
Scalable Observability
apache-arrow datafusion flight-sql logging metrics observability time-series traces rust unreal-engine-5 python fdap parquet
Rust C++ C Batchfile Python Dockerfile C# HTML Shell Jupyter Notebook
All Public RunWhen Helm Charts - Managed by terraform
Shell Dockerfile Go Template
None
Shell Python
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-21441 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-21441 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.
-
CVE Modified by af854a3a-2127-422b-91ae-364da2661108
Jan. 23, 2026
Action Type Old Value New Value Added Reference https://lists.debian.org/debian-lts-announce/2026/01/msg00017.html -
Initial Analysis by [email protected]
Jan. 15, 2026
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) 1.22 up to (excluding) 2.6.3 Added Reference Type GitHub, Inc.: https://github.com/urllib3/urllib3/commit/8864ac407bba8607950025e0979c4c69bc7abc7b Types: Patch Added Reference Type GitHub, Inc.: https://github.com/urllib3/urllib3/security/advisories/GHSA-38jv-5279-wg99 Types: Vendor Advisory -
New CVE Received by [email protected]
Jan. 07, 2026
Action Type Old Value New Value Added Description urllib3 is an HTTP client library for Python. urllib3's streaming API is designed for the efficient handling of large HTTP responses by reading the content in chunks, rather than loading the entire response body into memory at once. urllib3 can perform decoding or decompression based on the HTTP `Content-Encoding` header (e.g., `gzip`, `deflate`, `br`, or `zstd`). When using the streaming API, the library decompresses only the necessary bytes, enabling partial content consumption. Starting in version 1.22 and prior to version 2.6.3, for HTTP redirect responses, the library would read the entire response body to drain the connection and decompress the content unnecessarily. This decompression occurred even before any read methods were called, and configured read limits did not restrict the amount of decompressed data. As a result, there was no safeguard against decompression bombs. A malicious server could exploit this to trigger excessive resource consumption on the client. Applications and libraries are affected when they stream content from untrusted sources by setting `preload_content=False` when they do not disable redirects. Users should upgrade to at least urllib3 v2.6.3, in which the library does not decode content of redirect responses when `preload_content=False`. If upgrading is not immediately possible, disable redirects by setting `redirect=False` for requests to untrusted source. 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-409 Added Reference https://github.com/urllib3/urllib3/commit/8864ac407bba8607950025e0979c4c69bc7abc7b Added Reference https://github.com/urllib3/urllib3/security/advisories/GHSA-38jv-5279-wg99