{"id":"CVE-2026-55368","title":"h2o: buffer overflow when using the %{error}x log directive","summary":"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 c…","severity":"high","cvss":8.1,"cvssVector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H","cvssSource":"cna","cwe":["CWE-787"],"vendor":"h2o","product":"h2o","affected":["h2o < 48b7ae12107fd2b118e4641da49599e9aac8edd8"],"published":"2026-11-04","updated":"2026-11-04","sourceUpdated":"2026-11-04T21:38:04.613Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-55368","references":[{"url":"https://github.com/h2o/h2o/security/advisories/GHSA-m998-r5ww-rqjf","label":"https://github.com/h2o/h2o/security/advisories/GHSA-m998-r5ww-rqjf"},{"url":"https://github.com/h2o/h2o/pull/3757","label":"https://github.com/h2o/h2o/pull/3757"},{"url":"https://github.com/h2o/h2o/commit/48b7ae12107fd2b118e4641da49599e9aac8edd8","label":"https://github.com/h2o/h2o/commit/48b7ae12107fd2b118e4641da49599e9aac8edd8"}],"tags":["cve.org"],"ingestedAt":"2026-11-05T21:36:00.621Z","epss":0.00321,"epssPercentile":0.25234,"slug":"CVE-2026-55368","body":"## Overview\n\nh2o 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.\n\n## Affected\n\n- `h2o < 48b7ae12107fd2b118e4641da49599e9aac8edd8`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":45,"depthScoreParts":{"impact":44.6,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}