PT-2017-8994 · Python · Python Hpack Library

Published 2017-01-10 · Updated 2026-06-08 · CVE-2016-6581

Positive Technologies (AI Summary)

CVSS v4.0

8.7

High

Base vector

AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Name of the Vulnerable Software and Affected Versions Python HPACK library versions 1.0.0 through 2.2.0

Description A denial of service attack, known as an "HPACK Bomb" attack, can be launched against the HTTP/2 implementation built using the Python HPACK library. This occurs when an attacker inserts a header field of a specific size into the dynamic header table, then sends repeated requests to expand this field, resulting in a high compression ratio. For example, 16kB of data can decompress to 64MB of data on the target machine.

Recommendations For versions 1.0.0 through 2.2.0, consider disabling the HTTP/2 implementation until a patch is available to prevent the "HPACK Bomb" attack. Restrict access to the dynamic header table to minimize the risk of exploitation. Avoid using the Python HPACK library for HTTP/2 implementations until the issue is resolved.

Fix

Weakness Enumeration

CWE-399

Related Identifiers

BDU:2026-08138

CVE-2016-6581

GHSA-FFQ8-576R-V26G

OPENSUSE-SU-2024:11230-1

OPENSUSE-SU-2024:14140-1

PYSEC-2017-87

Affected Products

Python Hpack Library

References · 25

• https://ubuntu.com/security/CVE-2016-6581 · Vendor Advisory
• https://osv.dev/vulnerability/DEBIAN-CVE-2016-6581 · Vendor Advisory
• https://nvd.nist.gov/vuln/detail/CVE-2016-6581 · Security Note
• https://osv.dev/vulnerability/PYSEC-2017-87 · Vendor Advisory
• https://cve.org/CVERecord?id=CVE-2016-6581 · Security Note
• https://python-hyper.org/hpack/en/latest/security/CVE-2016-6581.html · Vendor Advisory
• https://osv.dev/vulnerability/GHSA-ffq8-576r-v26g · Vendor Advisory
• https://osv.dev/vulnerability/openSUSE-SU-2024:14140-1 · Vendor Advisory
• https://osv.dev/vulnerability/UBUNTU-CVE-2016-6581 · Vendor Advisory
• https://security-tracker.debian.org/tracker/CVE-2016-6581 · Vendor Advisory
• https://osv.dev/vulnerability/CVE-2016-6581 · Vendor Advisory
• https://bdu.fstec.ru/vul/2026-08138 · Security Note
• https://github.com/pypa/advisory-database/tree/main/vulns/hpack/PYSEC-2017-87.yaml · Note
• https://github.com/python-hyper/hpack · Note
• https://github.com/python-hyper/hpack/pull/56 · Note