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CVE-2026-97688

urllib3 is an HTTP client library for Python.

Published Sep 29, 2026 · updated Oct 14, 2026 · Canonical Ubuntu

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.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 14, 2026 · Ubuntu Security Notices

    Detected

    Yu-Fu Fu, Seth Larson and Yonatan Magier discovered that urllib3 did not correctly handle certain certificate validations. An attacker could possibly use this issue to observe or modify forwarded traffic. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-97687) Martin Desrumaux discovered that urllib3 did not correctly handle decoding certain deflate responses. An attacker could possibly use th

  2. Oct 14, 2026 · OSV.dev

    Updated

    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 pos

Affected

  • Ubuntu:22.04:LTS python-urllib31.26.5-1~exp1, 1.26.5-1~exp1ubuntu0.1, 1.26.5-1~exp1ubuntu0.2
  • Ubuntu:24.04:LTS python-urllib31.26.16-1, 1.26.18-1, 2.0.7-1
  • Ubuntu:Pro:14.04:LTS python-pip1.4.1-2, 1.5.4-1, 1.5.4-1ubuntu1
  • Ubuntu:Pro:14.04:LTS python-urllib31.6-2, 1.7.1-1, 1.7.1-1build1
  • Ubuntu:Pro:16.04:LTS python-pip1.5.6-7ubuntu1, 1.5.6-7ubuntu2, 8.0.2-7
  • Ubuntu:Pro:16.04:LTS python-urllib31.11-1, 1.12-1, 1.13.1-1
  • Ubuntu:Pro:18.04:LTS python-pip9.0.1-2, 9.0.1-2.3~ubuntu1, 9.0.1-2.3~ubuntu1.18.04.1
  • Ubuntu:Pro:18.04:LTS python-urllib31.21.1-1, 1.22-1, 1.22-1ubuntu0.18.04.1
  • Ubuntu:Pro:20.04:LTS python-pip18.1-5, 18.1-5build1, 18.1-5ubuntu1
  • Ubuntu:Pro:20.04:LTS python-urllib31.24.1-1ubuntu1, 1.24.1-1ubuntu2, 1.25.8-1
  • Ubuntu:Pro:22.04:LTS python-pip20.3.4-4, 21.3.1+dfsg-3, 22.0.2+dfsg-1
  • Ubuntu:Pro:24.04:LTS python-pip23.2+dfsg-1, 23.3+dfsg-1, 24.0+dfsg-1

Sources

  • CVE.orgVulnerability recordCVE-2026-97688

    Official CVE identifier

    cve.org
  • OSV.devPackage advisoryUBUNTU-CVE-2026-97688
    osv.dev
  • Ubuntu Security NoticesVendor advisoryCVE-2026-97688

    Yu-Fu Fu, Seth Larson and Yonatan Magier discovered that urllib3 did not correctly handle certain certificate validations. An attacker could possibly use this issue to observe or modify forwarded traffic. This issue only affected Ubuntu 26.04 LTS. (CVE-2026-97687) Martin Desrumau

    ubuntu.com

References