{"id":"UBUNTU-CVE-2016-6581","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.","modified":"2025-10-24T04:45:51Z","published":"2017-01-10T15:59:00Z","upstream":["CVE-2016-6581"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2016-6581"},{"type":"REPORT","url":"https://github.com/python-hyper/hpack/pull/56"},{"type":"REPORT","url":"http://www.openwall.com/lists/oss-security/2016/08/04/3"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2016-6581"}],"affected":[{"package":{"name":"python-hpack","ecosystem":"Ubuntu:16.04:LTS","purl":"pkg:deb/ubuntu/python-hpack@2.1.0-1?arch=source&distro=xenial"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.1.0-1","2.0.1-1","2.1.0-1"],"ecosystem_specific":{"binaries":[{"binary_name":"python-hpack","binary_version":"2.1.0-1"},{"binary_name":"python3-hpack","binary_version":"2.1.0-1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2016/UBUNTU-CVE-2016-6581.json"}}],"schema_version":"1.7.3","severity":[{"type":"CVSS_V3","score":"CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},{"type":"Ubuntu","score":"medium"}]}