Medium 6.3Published Sep 23, 2026

CVE-2026-59980hpack: Unbounded variable integer decoding can cause run-away computation on malformed input

Updated under an hour ago (Oct 27, 2026, 9:50 AM ET)

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No exploitation reported and no EPSS estimate yet.

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Every CVE for python-hyper hpack

Exploited in the last 30 days

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.

CVSS: 6.3 MEDIUM (v4.0, CNA)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
Weakness (CWE): CWE-400
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: GitHub_M
NVD analysis: Deferred
Record last updated: Sep 24, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

python-hyper hpack python_hyper:hpack (from the name)	before 4.2.0	CNA record

References

References

https://github.com/python-hyper/hpack/security/advisories/GHSA-8v8h-hg4w-mvq2	x-refsource-confirm
https://github.com/python-hyper/hpack/commit/8cfb02c547740e16dbfe7aba77bad84b297cec2c	x-refsource-misc
https://cs.opensource.google/go/x/net/+/master:http2/hpack/hpack.go;l=468;drc=8e2b117aee74f6b86c207a808b0255de45c0a18a	x-refsource-misc
https://docs.rs/http2/0.5.19/src/http2/hpack/decoder.rs.html#403	x-refsource-misc

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.