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Fencer Intel
medium 6.3

CVE-2026-59980 json

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

published 4mo ago modified last mo. also EUVD-2026-85712 , GHSA-8v8h-hg4w-mvq2 , PYSEC-2026-4053

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 hyper 4.2.0
  • python 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

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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
last mo.

Exploit prediction

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

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 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 python-hyper/hpack 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.