urllib3 is an HTTP client library for Python. From 2.6.2 until 2.8.0, HTTPResponse.stream and HTTPResponse.read_chunked can enter an infinite loop because the Deflate decoder retains trailing bytes as unconsumed input after reaching end-of-stream and repeatedly decodes them without progress. The issue occurs when an untrusted server sends a chunked Deflate response whose decoded body exceeds a positive finite chunk size and whose encoded body has trailing bytes, specifically a response with Transfer-Encoding: chunked and Content-Encoding: deflate, content decoding enabled, and the positive finite amt=N streaming chunk size. The attack mechanism is that a malicious server returns a compressed chunked response with trailing bytes after the Deflate stream. The impact is excessive CPU usage and a request that does not complete, and network read timeouts do not interrupt the loop because no further socket read occurs. This issue is fixed in version 2.8.0.
References
| Link | Resource |
|---|---|
| https://github.com/urllib3/urllib3/commit/ea2ad7b21a80da3632f80016526a18864586077f | Patch |
| https://github.com/urllib3/urllib3/releases/tag/2.8.0 | Release Notes |
| https://github.com/urllib3/urllib3/security/advisories/GHSA-gh4c-6fx4-qh6g | Mitigation Vendor Advisory |
Configurations
History
13 Oct 2026, 20:21
| Type | Values Removed | Values Added |
|---|---|---|
| References | () https://github.com/urllib3/urllib3/commit/ea2ad7b21a80da3632f80016526a18864586077f - Patch | |
| References | () https://github.com/urllib3/urllib3/releases/tag/2.8.0 - Release Notes | |
| References | () https://github.com/urllib3/urllib3/security/advisories/GHSA-gh4c-6fx4-qh6g - Mitigation, Vendor Advisory | |
| CPE | cpe:2.3:a:python:urllib3:*:*:*:*:*:*:*:* | |
| First Time |
Python urllib3
Python |
|
| CVSS |
v2 : v3 : |
v2 : unknown
v3 : 5.3 |
29 Sep 2026, 16:17
| Type | Values Removed | Values Added |
|---|---|---|
| New CVE |
Information
Published : 2026-09-29 16:17
Updated : 2026-10-13 20:21
NVD link : CVE-2026-97688
Mitre link : CVE-2026-97688
CVE.ORG link : CVE-2026-97688
JSON object : View
Products Affected
python
- urllib3
CWE
CWE-835
Loop with Unreachable Exit Condition ('Infinite Loop')
