CVE-2026-59980

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

Published: Sep 23, 2026Updated: Sep 23, 2026 Sources: CVE List NVDCWE-400

N/ACVSS

NVD MITRE

Description

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.

No summary for this CVE yet.

Weaknesses

CWE-400

Affected Products

python-hyper

oss-project

hpackLibrary

OSS Libraries / generic-library

Exploitability

No known exploits, KEV entries, or remediation guidance available for this vulnerability yet.

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References

https://github.com/python-hyper/hpack/security/advisories/GHSA-8v8h-hg4w-mvq2

github.com

https://github.com/python-hyper/hpack/commit/8cfb02c547740e16dbfe7aba77bad84b297cec2c

github.com

https://cs.opensource.google/go/x/net/+/master:http2/hpack/hpack.go;l=468;drc=8e2b117aee74f6b86c207a808b0255de45c0a18a

cs.opensource.google

and 1 more references View all →

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