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CVE-2026-59980

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

CVSS 4.0 6.3 MEDIUMCheck source for fixed versionsKEV status unknown

Original advisory

Historical advisory recorded 23 Oct 2026 15:48:27 UTC. Read the latest advisory.

cve-program · CVE-2026-59980

Published

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.

Read the publisher's advisory

Affected versions, risk and source history

cve-program · CVE-2026-59980

Published

hpack

Vendor product

Publisher's version information

Shown as published. These rules are not interpreted as NuGet package version ranges.

{
                    "vendor": "python-hyper",
                    "product": "hpack",
                    "versions": [
                        {
                            "version": "< 4.2.0",
                            "status": "affected"
                        }
                    ]
                }

Original source record · Cite this exact observation · Complete original publisher JSON