{"id":"CVE-2016-6581","aliases":["GHSA-ffq8-576r-v26g","PYSEC-2017-87"],"url":"https://o3.security/vulnerability/CVE-2016-6581","summary":"HPACK Denial of Service vulnerability (HPACK Bomb)","details":"A HTTP/2 implementation built using any version of the Python HPACK library between v1.0.0 and v2.2.0 could be targeted for a denial of service attack, specifically a so-called \"HPACK Bomb\" attack. This attack occurs when an attacker inserts a header field that is exactly the size of the HPACK dynamic header table into the dynamic header table. The attacker can then send a header block that is simply repeated requests to expand that field in the dynamic table. This can lead to a gigantic compression ratio of 4,096 or better, meaning that 16kB of data can decompress to 64MB of data on the target machine.","published":"2017-01-10T15:59:00.423Z","modified":"2026-10-24T10:30:58.406113051Z","cvss":{"score":7.5,"severity":"HIGH","vector":"CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"PyPI","name":"hpack","fixedVersion":"2.3.0"}],"fix":null,"references":[{"type":"ADVISORY","url":"http://www.securityfocus.com/bid/92315"},{"type":"ADVISORY","url":"https://python-hyper.org/hpack/en/latest/security/CVE-2016-6581.html"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2016-6581"},{"type":"ADVISORY","url":"https://github.com/advisories/GHSA-ffq8-576r-v26g"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/hpack/PYSEC-2017-87.yaml"},{"type":"PACKAGE","url":"https://github.com/python-hyper/hpack"},{"type":"WEB","url":"https://web.archive.org/web/20200227233559/http://www.securityfocus.com/bid/92315"},{"type":"WEB","url":"http://python-hyper.org/projects/hpack/en/stable/security/CVE-2016-6581.html"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-24T10:30:58.406113051Z"}}