{"id":"UBUNTU-CVE-2026-55368","details":"h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 48b7ae12107fd2b118e4641da49599e9aac8edd8, H2O's access-log formatter could write past its log-line buffer when an affected custom access-log format was configured. The allocation errors affected %{error}x, %q when the query string was empty, and numeric elements whose temporary terminating NUL reached the end of the buffer. A matching request could crash the server, while the effect of the one-byte NUL overwrite beyond a crash was not established. This vulnerability is fixed with commit 48b7ae12107fd2b118e4641da49599e9aac8edd8.","modified":"2026-11-06T01:01:07.465423191Z","published":"2026-11-05T00:00:00Z","upstream":["CVE-2026-55368"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-55368"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-55368"},{"type":"REPORT","url":"https://github.com/h2o/h2o/security/advisories/GHSA-m998-r5ww-rqjf"},{"type":"REPORT","url":"https://github.com/h2o/h2o/pull/3757"},{"type":"REPORT","url":"https://github.com/h2o/h2o/commit/48b7ae12107fd2b118e4641da49599e9aac8edd8"}],"affected":[{"package":{"name":"h2o","ecosystem":"Ubuntu:Pro:18.04:LTS","purl":"pkg:deb/ubuntu/h2o?arch=source&distro=esm-apps%2Fbionic"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.2.3+dfsg-2","2.2.4+dfsg-1","2.2.4+dfsg-1build1","2.2.4+dfsg-1ubuntu0.1~esm2"],"ecosystem_specific":{"binaries":[{"binary_version":"2.2.4+dfsg-1ubuntu0.1~esm2","binary_name":"h2o"},{"binary_name":"libh2o-dev-common","binary_version":"2.2.4+dfsg-1ubuntu0.1~esm2"},{"binary_version":"2.2.4+dfsg-1ubuntu0.1~esm2","binary_name":"libh2o-evloop0.13"},{"binary_version":"2.2.4+dfsg-1ubuntu0.1~esm2","binary_name":"libh2o0.13"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-55368.json"}},{"package":{"name":"h2o","ecosystem":"Ubuntu:Pro:20.04:LTS","purl":"pkg:deb/ubuntu/h2o?arch=source&distro=esm-apps%2Ffocal"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.2.5+dfsg2-3","2.2.5+dfsg2-3build1","2.2.5+dfsg2-3ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"h2o","binary_version":"2.2.5+dfsg2-3ubuntu0.1~esm1"},{"binary_name":"libh2o-dev-common","binary_version":"2.2.5+dfsg2-3ubuntu0.1~esm1"},{"binary_version":"2.2.5+dfsg2-3ubuntu0.1~esm1","binary_name":"libh2o-evloop0.13"},{"binary_name":"libh2o0.13","binary_version":"2.2.5+dfsg2-3ubuntu0.1~esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-55368.json"}},{"package":{"name":"h2o","ecosystem":"Ubuntu:Pro:22.04:LTS","purl":"pkg:deb/ubuntu/h2o?arch=source&distro=esm-apps%2Fjammy"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.2.5+dfsg2-6","2.2.5+dfsg2-6.1","2.2.5+dfsg2-6.1ubuntu1","2.2.5+dfsg2-6.1ubuntu2","2.2.5+dfsg2-6.1ubuntu2+esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"h2o","binary_version":"2.2.5+dfsg2-6.1ubuntu2+esm1"},{"binary_version":"2.2.5+dfsg2-6.1ubuntu2+esm1","binary_name":"libh2o-dev-common"},{"binary_name":"libh2o-evloop0.13","binary_version":"2.2.5+dfsg2-6.1ubuntu2+esm1"},{"binary_name":"libh2o0.13","binary_version":"2.2.5+dfsg2-6.1ubuntu2+esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-55368.json"}},{"package":{"name":"h2o","ecosystem":"Ubuntu:24.04:LTS","purl":"pkg:deb/ubuntu/h2o?arch=source&distro=noble"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.2.5+dfsg2-7","2.2.5+dfsg2-8","2.2.5+dfsg2-8.1ubuntu1","2.2.5+dfsg2-8.1ubuntu2","2.2.5+dfsg2-8.1ubuntu3"],"ecosystem_specific":{"binaries":[{"binary_name":"h2o","binary_version":"2.2.5+dfsg2-8.1ubuntu3"},{"binary_version":"2.2.5+dfsg2-8.1ubuntu3","binary_name":"libh2o-dev-common"},{"binary_version":"2.2.5+dfsg2-8.1ubuntu3","binary_name":"libh2o-evloop0.13t64"},{"binary_name":"libh2o0.13t64","binary_version":"2.2.5+dfsg2-8.1ubuntu3"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-55368.json"}},{"package":{"name":"dnsdist","ecosystem":"Ubuntu:Pro:24.04:LTS","purl":"pkg:deb/ubuntu/dnsdist?arch=source&distro=esm-apps%2Fnoble"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.8.0-1","1.8.2-1","1.8.2-2","1.8.2-3","1.8.3-1","1.8.3-2","1.8.3-2build1","1.8.3-2build2","1.8.3-2ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"dnsdist","binary_version":"1.8.3-2ubuntu0.1~esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-55368.json"}}],"schema_version":"1.9.2","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H"},{"type":"Ubuntu","score":"medium"}]}