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Fencer Intel
medium 5.3

CVE-2026-97688 json

urllib3: Chunked Deflate streaming can enter an infinite loop

published last mo. modified 29d ago also EUVD-2026-89007 , GHSA-gh4c-6fx4-qh6g , PYSEC-2026-4176

cvss
5.3
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 22%
public exploits
0
none known

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-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.

Patch / fix

  • pypi urllib3 2.8.0
  • python urllib3 2.8.0
  • python-urllib3 Debian 14 2.8.0-1

debian advisories DEBIAN-CVE-2026-97688

  • python-urllib3 Ubuntu 26.04 LTS 2.6.3-1ubuntu1.2

ubuntu advisories UBUNTU-CVE-2026-97688

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • python-urllib3 hummingbird 1 2.8.0-1.hum1
  • python3-urllib3 hummingbird 1 2.8.0-1.hum1
  • python3-urllib3+h2 hummingbird 1 2.8.0-1.hum1
  • python3-urllib3+zstd hummingbird 1 2.8.0-1.hum1
  • python3-urllib3+socks hummingbird 1 2.8.0-1.hum1
  • python3-urllib3+brotli hummingbird 1 2.8.0-1.hum1

red hat advisories RHSA-2026:69612

  • python-urllib3_1 SLES for SAP 15 SP6, SLES 15 SP6-LTSS, SLE Module for Python 3 15 SP7 1.26.18-150600.3.14.1
  • python-urllib3 SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +9 more 2.0.7-150400.7.36.1
  • python-urllib3 SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +11 more 1.25.10-150300.4.33.1
  • python-urllib3 SLES LTSS Extended Security 12 SP5, SLES 12 SP5-LTSS, SLE Module for Public Cloud 12 1.25.10-3.54.1
  • python-urllib3 SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 2.5.0-160000.8.1

suse advisories SUSE-SU-2026:4948-1SUSE-SU-2026:4704-1SUSE-SU-2026:4650-1SUSE-SU-2026:4649-1SUSE-SU-2026:24125-1SUSE-SU-2026:24217-1

  • python-urllib3_1 openSUSE Leap 16.0 1.26.20-160000.5.1
  • python-urllib3_1 openSUSE Tumbleweed 1.26.20-8.1
  • python-urllib3 openSUSE Leap 16.0 2.5.0-160000.8.1
  • python-urllib3 openSUSE Tumbleweed 2.8.0-1.1

opensuse advisories openSUSE-SU-2026:22252-1openSUSE-SU-2026:12119-1openSUSE-SU-2026:22071-1openSUSE-SU-2026:12044-1

Is CVE-2026-97688 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

Check with Fencer

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-97688 updated cvss 5.3

urllib3: urllib3: Denial of Service via infinite loop during chunked Deflate decoding

  • Red Hat OpenShift AI (RHOAI) rhoai/odh-mlflow-rhel9
    affected: no fix available “Fix deferred”
  • Red Hat AI Inference Server 3.4 rhaii/vllm-cpu-rhel9 1791857301, rhaii/vllm-cuda-rhel9 1791857183, rhaii/vllm-rocm-rhel9 1791856725, rhaii/vllm-spyre-rhel9 1791858592, rhaii/model-opt-cuda-rhel9 1791857110
    fixed: vendor fix RHSA-2026:83116
  • Red Hat AI Inference Server 3.5 rhaii/vllm-cpu-rhel9 1791473614, rhaii/vllm-cuda-rhel9 1791473631, rhaii/vllm-rocm-rhel9 1791425869, rhaii/vllm-gaudi-rhel9 1791427182, rhaii/vllm-spyre-rhel9 1791818357
    fixed: vendor fix RHSA-2026:82415
  • Red Hat Enterprise Linux AI 3.4 rhelai3/bootc-cuda-rhel9 1792612985, rhelai3/bootc-rocm-rhel9 1792612921, rhelai3/bootc-aws-cuda-rhel9 1792680701, rhelai3/bootc-gcp-cuda-rhel9 1792680694, rhelai3/disk-image-cuda-rhel9 1792701796, rhelai3/bootc-azure-cuda-rhel9 1792680694, +1 more
    fixed: vendor fix RHSA-2026:90440
  • Red Hat Enterprise Linux AI 3.5 rhelai3/bootc-cuda-rhel9 1793135861, rhelai3/bootc-rocm-rhel9 1793135863, rhelai3/bootc-aws-cuda-rhel9 1793194817, rhelai3/bootc-gcp-cuda-rhel9 1793194815, rhelai3/disk-image-cuda-rhel9 1793206758, rhelai3/bootc-azure-cuda-rhel9 1793194815, +1 more
    fixed: vendor fix RHSA-2026:92452
  • Red Hat Hardened Images python-urllib3 2.8.0-1.hum1, python3-urllib3 2.8.0-1.hum1, python3-urllib3+h2 2.8.0-1.hum1, python3-urllib3+zstd 2.8.0-1.hum1, python3-urllib3+socks 2.8.0-1.hum1, python3-urllib3+brotli 2.8.0-1.hum1
    fixed: vendor fix RHSA-2026:69612
  • Red Hat Hardened Images rust 1.98.1-1.hum1, llvm21 21.1.8-10.hum1, trivy 0.74.0-0.4.hum1, jaeger 2.20.0-0.11.hum1, swift-lang 6.4.0-0.5.hum1, grafana13.1 13.1.6-0.4.hum1, +8 more
    not affected: component not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
last mo.

Exploit prediction

0.29% chance of exploitation in the next 30 days, higher than 22% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CNA 4.0 6.9 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
CNA 4.0 6.9 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/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
NVD 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Affected packages

ecosystem package affected fixed in
pypi urllib3
>=2.6.2, <2.8.0
2.8.0

Affected products

  • urllib3 urllib3

Classification

Weakness
  • CWE-835 Loop with Unreachable Exit Condition

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

The maintainers of urllib3/urllib3 published their own advisory on GitHub. Reviewed sources take precedence over it.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.