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VulnerabilityCVE-2026-59980Published 2026-09-23

CVE-2026-59980 — python-hyper hpack

medium (derived)

As of 2026-09-24, CVE-2026-59980 is a Medium-severity (band derived from the CVSS v4.0 score, not stated by the CNA) vulnerability in python-hyper hpack, CVSS v4.0 6.3, EPSS 0.3% (20.2th percentile). No Threadlinqs-tracked threat campaign has been attributed to CVE-2026-59980 as of 2026-09-24; the identifier is re-checked against the Threadlinqs threat corpus on every daily ingest.

CVSS v4.0
6.3/10Medium (derived)
EPSS
0.3%Higher than 20.2% of scored CVEs
CISA KEV
NoNot in the KEV catalog
Tracked threats
0None linked yet
Priority
4/10Threadlinqs triage score
Published
Updated 2026-09-24
CVSS v4.0 6.3 (Medium, derived from score) · EPSS 0.3% (higher than 20.2% of all scored CVEs) · Priority 4/10 · Published 2026-09-23

Last updated:

What is CVE-2026-59980?

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.

The record classifies CVE-2026-59980 under weakness class CWE-400. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 12 days ago.

Severity and exploitation probability

CVSS v4.0 base score
6.3 — Medium (derived from score)
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
EPSS (FIRST)
0.3% probability of exploitation in the next 30 days, higher than 20.2% of all scored CVEs
CISA KEV
Not listed in the CISA Known Exploited Vulnerabilities catalog
Threadlinqs priority
4/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
Published
2026-09-23, last modified 2026-09-24

Is CVE-2026-59980 being exploited?

It currently carries a trending score of 35 in the Threadlinqs vulnerability feed.

Affected products and versions

  • python-hyper: hpack

How to fix CVE-2026-59980

No vendor patch reference has been recorded for CVE-2026-59980 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

Threat activity tracking CVE-2026-59980

No threat campaign in the Threadlinqs corpus currently references CVE-2026-59980, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.

Sources

Enriched from CVE.org, NVD, FIRST EPSS. Last verified by Threadlinqs on . This product uses the NVD API but is not endorsed or certified by the NVD.

Vendor advisory and patch

Other references