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.

suse_linux SUSE-SU-2026:4593-1: SUSE SLES15 : Security update for python-hpack (Moderate) (SUSE-SU-2026:4593-1)

It is, therefore, affected by a vulnerability as referenced in the ALAS2023-2026-3159 advisory.

    A flaw was found in hpack, an HTTP/2 Header Encoding for Python. Unbounded variable integer decoding can     lead to excessive computation when processing specially crafted, malformed input. A remote attacker could     exploit this vulnerability to cause a denial of service by effectively blocking further processing within     the affected component. (CVE-2026-59980)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - 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. (CVE-2026-59980)

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - 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. (CVE-2026-59980)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Type	Severity
365281	Amazon Linux 2023 : python3-hpack (ALAS2023-2026-3159)	Nessus	Amazon Linux Local Security Checks	Local	medium
459372	Echo: hpack: security update to 4.2.0	Tenable Cloud Security	Echo Local Security Checks	Local	medium
459372	Echo: hpack: security update to 4.2.0	Tenable Self-Hosted Container Security	Echo Local Security Checks	Local	medium
448357	SCA: security update for hpack (GHSA-8v8h-hg4w-mvq2)	Tenable Cloud Security	SCA Checks	Local	medium
448357	SCA: security update for hpack (GHSA-8v8h-hg4w-mvq2)	Tenable Self-Hosted Container Security	SCA Checks	Local	medium
350233	Linux Distros Unpatched Vulnerability : CVE-2026-59980	Nessus	Misc.	Local	medium

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