---
id: CVE-2026-97688
title: urllib3 is an HTTP client library for Python
summary: >-
  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-…
severity: medium
cvss: 6.9
cvssVector: 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N'
cwe:
  - CWE-835
vendor: urllib3
product: urllib3
affected:
  - 'urllib3 >= 2.6.2, < 2.8.0'
published: '2026-09-29'
updated: '2026-09-29'
sourceUpdated: '2026-09-29T16:17:18.680'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-97688'
references:
  - url: >-
      https://github.com/urllib3/urllib3/commit/ea2ad7b21a80da3632f80016526a18864586077f
    label: security-advisories@github.com
  - url: 'https://github.com/urllib3/urllib3/releases/tag/2.8.0'
    label: security-advisories@github.com
  - url: 'https://github.com/urllib3/urllib3/security/advisories/GHSA-gh4c-6fx4-qh6g'
    label: security-advisories@github.com
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-29T15:42:28.931695Z'
cvssSource: cna
ingestedAt: '2026-09-29T16:39:33.273Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.