How severe is CVE-2026-59980?

No CVSS score has been assigned to CVE-2026-59980 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-59980?

CVE-2026-59980 affects the following packages: hpack (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2026-59980?

Update hpack to 4.2.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-59980 is resolved across your whole dependency graph.

How do I detect CVE-2026-59980 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hpack, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-59980 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2026-59980 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-59980 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-59980?

CVE-2026-59980 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 22th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-59980?

CVE-2026-59980 is classified as Uncontrolled Resource Consumption (CWE-400). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-59980 published, and has it been updated?

CVE-2026-59980 was published on September 23, 2026 and was last updated on October 22, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍 PyPI

Not in CISA KEV

CVE-2026-59980 — hpack

Fix: python-hyper/hpack@8cfb02c

CVE-2026-59980 is a Uncontrolled Resource Consumption vulnerability in hpack. A fix is available for hpack — see the affected versions and patch details below.

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

Also known asGHSA-8v8h-hg4w-mvq2PYSEC-2026-4053

Published

Sep 23, 2026

Updated

Oct 22, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 22, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-59980.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs22th percentile — riskier than 22% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

🐍hpack

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

Impact

Users of the python-hyper/hpack library, most commonly used as downstream dependency of the python-hyper/h2 library (an HTTP/2 client and server implementation). 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.

Patches

A fix is available in python-hyper/hpack v4.2.0 to restricted variable integer decoding to uint32 to prevent run-away computation.

Workarounds

Sanitize input to hpack decoder for long sequences of 0xFF values to prevent malicious use.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`hpack`	all versions	4.2.0`pip install --upgrade 'hpack==4.2.0'`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for hpack, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update hpack to 4.2.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-59980 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatLow

A flaw was found in hpack, the Python HTTP/2 header encoding library, which is shipped as a dependency in several Red Hat products, including Red Hat OpenStack Platform, Red Hat Ansible Automation Platform, Red Hat OpenShift AI, Migration Toolkit for Containers, and cloud.redhat.com services. The library performs…

Workaround published by Red Hat

Sanitize input to hpack decoder for long sequences of `0xFF` values to prevent malicious use.

Source: Red Hat security advisory for CVE-2026-59980 (CC BY 4.0)

Frequently Asked Questions

### Impact Users of the python-hyper/hpack library, most commonly used as downstream dependency of the python-hyper/h2 library (an HTTP/2 client and server implementation). 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. ### Patches A fix is available in python-hyper/hpack v4.2.0 to restricted variable integer decoding to uint32 to prevent run-away computation. ### Workarounds Sanitize input to hpack decoder for long sequences of `0xFF` values to prev

O3 Security · Impact-Aware SCA

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