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CVE-2026-59980

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

This page contains facts from public vulnerability sources. Check the original advisory before updating.

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 · EPSS 0.3% · Fix available

Published
Updated

Stack: system · python

Affected products and versions

  • hpack

    Versions
    • < 4.2.0: Affected

    No fix published

  • python-hpack Debian:12

    Versions
    • 4.0.0-2
    • 4.0.0-3
    • 4.0.0-4
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-hpack Debian:13

    Versions
    • 4.0.0-3
    • 4.0.0-4
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-hpack Debian:14

    Versions
    • 4.0.0-3
    • 4.0.0-4
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • hpack PyPI

    Versions
    • 1.0.0
    • 1.0.1
    • 1.1.0
    • 2.0.0
    • 2.0.1
    • 2.1.0
    • 2.1.1
    • 2.2.0
    • 2.3.0
    • 3.0.0
    • 4.0.0
    • 4.1.0
    Affected ranges
    • ECOSYSTEM: < 4.2.0

    Update to 4.2.0

  • python-hpack Ubuntu:16.04:LTS

    Versions
    • 1.1.0-1
    • 2.0.1-1
    • 2.1.0-1
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-hpack Ubuntu:18.04:LTS

    Versions
    • 3.0.0-1
    • 3.0.0-2
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-hpack Ubuntu:20.04:LTS

    Versions
    • 3.0.0-3
    • 3.0.0-4
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-hpack Ubuntu:22.04:LTS

    Versions
    • 4.0.0-2
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-hpack Ubuntu:24.04:LTS

    Versions
    • 4.0.0-2
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-hpack Ubuntu:26.10

    Versions
    • 4.0.0-3
    • 4.0.0-4
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

  • python-hpack Ubuntu:26.04:LTS

    Versions
    • 4.0.0-3
    Affected ranges
    • ECOSYSTEM: (−∞, +∞)

    No fix published

Original sources

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