{"id":"UBUNTU-CVE-2026-31958","details":"Tornado is a Python web framework and asynchronous networking library. In versions of Tornado prior to 6.5.5, the only limit on the number of parts in multipart/form-data is the max_body_size setting (default 100MB). Since parsing occurs synchronously on the main thread, this creates the possibility of denial-of-service due to the cost of parsing very large multipart bodies with many parts. This vulnerability is fixed in 6.5.5.","modified":"2026-07-22T20:45:49.156207387Z","published":"2026-03-11T20:16:00Z","related":["USN-8198-1","USN-8198-2"],"upstream":["CVE-2026-31958"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-31958"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-31958"},{"type":"REPORT","url":"https://github.com/tornadoweb/tornado/security/advisories/GHSA-qjxf-f2mg-c6mc"},{"type":"ADVISORY","url":"https://ubuntu.com/security/notices/USN-8198-1"},{"type":"ADVISORY","url":"https://ubuntu.com/security/notices/USN-8198-2"}],"affected":[{"package":{"name":"python-tornado","ecosystem":"Ubuntu:Pro:16.04:LTS","purl":"pkg:deb/ubuntu/python-tornado?arch=source&distro=esm-infra%2Fxenial"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.2.1-1ubuntu3.1+esm3"}]}],"versions":["4.2.1-1ubuntu2","4.2.1-1ubuntu3","4.2.1-1ubuntu3.1","4.2.1-1ubuntu3.1+esm1","4.2.1-1ubuntu3.1+esm2"],"ecosystem_specific":{"availability":"Available with Ubuntu Pro (Infra-only): https://ubuntu.com/pro","binaries":[{"binary_name":"python-tornado","binary_version":"4.2.1-1ubuntu3.1+esm3"},{"binary_name":"python3-tornado","binary_version":"4.2.1-1ubuntu3.1+esm3"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-31958.json"}},{"package":{"name":"python-tornado","ecosystem":"Ubuntu:Pro:18.04:LTS","purl":"pkg:deb/ubuntu/python-tornado?arch=source&distro=esm-apps%2Fbionic"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"4.5.3-1ubuntu0.2+esm3"}]}],"versions":["4.5.1-2.1~build2","4.5.2-1","4.5.3-1","4.5.3-1ubuntu0.1","4.5.3-1ubuntu0.2","4.5.3-1ubuntu0.2+esm1","4.5.3-1ubuntu0.2+esm2"],"ecosystem_specific":{"binaries":[{"binary_version":"4.5.3-1ubuntu0.2+esm3","binary_name":"python-tornado"},{"binary_name":"python3-tornado","binary_version":"4.5.3-1ubuntu0.2+esm3"}],"availability":"Available with Ubuntu Pro: https://ubuntu.com/pro"},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-31958.json"}},{"package":{"name":"python-tornado","ecosystem":"Ubuntu:Pro:22.04:LTS","purl":"pkg:deb/ubuntu/python-tornado?arch=source&distro=esm-apps%2Fjammy"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.1.0-3ubuntu0.1~esm5"}]}],"versions":["6.1.0-1build1","6.1.0-2","6.1.0-3","6.1.0-3build1","6.1.0-3ubuntu0.1~esm1","6.1.0-3ubuntu0.1~esm2","6.1.0-3ubuntu0.1~esm4"],"ecosystem_specific":{"binaries":[{"binary_name":"python3-tornado","binary_version":"6.1.0-3ubuntu0.1~esm5"}],"availability":"Available with Ubuntu Pro: https://ubuntu.com/pro"},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-31958.json"}},{"package":{"name":"python-tornado","ecosystem":"Ubuntu:24.04:LTS","purl":"pkg:deb/ubuntu/python-tornado?arch=source&distro=noble"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.4.0-1ubuntu0.5"}]}],"versions":["6.3.2-1","6.4.0-0ubuntu1","6.4.0-1","6.4.0-1build1","6.4.0-1ubuntu0.1","6.4.0-1ubuntu0.2","6.4.0-1ubuntu0.4"],"ecosystem_specific":{"availability":"No subscription required","binaries":[{"binary_version":"6.4.0-1ubuntu0.5","binary_name":"python3-tornado"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-31958.json"}},{"package":{"name":"python-tornado","ecosystem":"Ubuntu:25.10","purl":"pkg:deb/ubuntu/python-tornado?arch=source&distro=questing"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.4.2-3ubuntu0.3"}]}],"versions":["6.4.2-1","6.4.2-2","6.4.2-2ubuntu1","6.4.2-3","6.4.2-3ubuntu0.2"],"ecosystem_specific":{"binaries":[{"binary_name":"python3-tornado","binary_version":"6.4.2-3ubuntu0.3"}],"availability":"No subscription required"},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-31958.json"}},{"package":{"name":"python-tornado","ecosystem":"Ubuntu:26.04:LTS","purl":"pkg:deb/ubuntu/python-tornado?arch=source&distro=resolute"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"6.5.4-0.1ubuntu0.1"}]}],"versions":["6.4.2-3","6.5.2-3","6.5.4-0.1"],"ecosystem_specific":{"binaries":[{"binary_name":"python3-tornado","binary_version":"6.5.4-0.1ubuntu0.1"}],"availability":"No subscription required"},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-31958.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"},{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},{"type":"Ubuntu","score":"medium"}]}