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Fencer Vulns
medium 6.3

CVE-2026-59980 json

hpack: Unbounded variable integer decoding can cause run-away computation on malformed input

published 2026-09-23 46 d ago modified 2026-10-01 38 d ago also GHSA-8v8h-hg4w-mvq2 , PYSEC-2026-4053 , EUVD-2026-85712

cvss
6.3
version 4.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 23%
public exploits
0
none known

Summary

hpack is an HTTP/2 Header Encoding for Python. Prior to version 4.2.0, unbounded variable integer decoding can cause run-away computation on malformed input leading to O(n^2) runtime, effectively blocking further processing with large enough unsanitized input. A fix is available in python-hyper/hpack v4.2.0 to restricted variable integer decoding to uint32 to prevent run-away computation. As a workaround, sanitize input to hpack decoder for long sequences of `0xFF` values to prevent malicious use.

Patch / fix

  • pypi hpack 4.2.0
  • python-hpack SLE Module for Python 3 15 SP7 4.0.0-150400.8.6.1
  • python-hpack SLES for SAP applications 16.0, SLES 16.0 4.1.0-160000.3.1
  • python-hpack SLE Module for Server Applications 15 SP7 3.0.0-150200.3.5.1

suse advisories SUSE-SU-2026:4832-1SUSE-SU-2026:24216-1SUSE-SU-2026:4593-1

  • python-hpack openSUSE Leap 16.0 4.1.0-160000.3.1
  • python-hpack openSUSE Tumbleweed 4.2.0-1.1

opensuse advisories openSUSE-SU-2026:22070-1openSUSE-SU-2026:11556-1

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-2026-59980 updated cvss 5.3

hpack: golang.org/x/net/http2/hpack: hpack: Denial of Service via malformed HTTP/2 header encoding

  • Red Hat Migration Toolkit for Containers rhmtc/openshift-migration-hook-runner-rhel8 Red Hat Ansible Automation Platform 2 ansible-automation-platform-24/ee-supported-rhel8, ansible-automation-platform-24/ee-supported-rhel9, ansible-automation-platform-25/ee-supported-rhel8, ansible-automation-platform-25/ee-supported-rhel9, ansible-automation-platform-26/ee-supported-rhel9, ansible-automation-platform-27/ee-supported-rhel9, +2 more Red Hat OpenShift AI (RHOAI) rhai/guidellm-rhel9, rhoai/odh-ogx-core-rhel9, rhoai/odh-feature-server-rhel9, rhoai/odh-llama-stack-core-rhel9 Red Hat OpenStack Platform 17.1 python3-hpack Red Hat OpenStack Platform 18.0 python-hpack 4.0.0-5.el9ost, rhoso/openstack-tempest-all-rhel9
    affected: workaround, no fix available “Sanitize input to hpack decoder for long sequences of `0xFF` values to prevent malicious use.”
  • Red Hat Hardened Images python-urllib3 2.8.0-1.hum1
    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
no
Technical impact
partial
Assessed
45 d ago

Exploit prediction

0.30% chance of exploitation in the next 30 days, higher than 23% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 6.3 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
CNA 4.0 6.3 CVSS:4.0/AV:N/AC:L/AT:P/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

Affected packages

ecosystem package affected fixed in
pypi hpack
<4.2.0
4.2.0

Affected products

  • python-hyper hpack

Classification

Weakness
  • CWE-400 Uncontrolled Resource Consumption

References

Sources

Fencer Vulns 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.