{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "h2o",
          "vendor": "h2o",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 48b7ae12107fd2b118e4641da49599e9aac8edd8"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 48b7ae12107fd2b118e4641da49599e9aac8edd8, H2O\u0027s 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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "HIGH",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 8.1,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "HIGH",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-787",
              "description": "CWE-787: Out-of-bounds Write",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-11-04T21:38:04.613Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/h2o/h2o/security/advisories/GHSA-m998-r5ww-rqjf",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/h2o/h2o/security/advisories/GHSA-m998-r5ww-rqjf"
        },
        {
          "name": "https://github.com/h2o/h2o/pull/3757",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/h2o/h2o/pull/3757"
        },
        {
          "name": "https://github.com/h2o/h2o/commit/48b7ae12107fd2b118e4641da49599e9aac8edd8",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/h2o/h2o/commit/48b7ae12107fd2b118e4641da49599e9aac8edd8"
        }
      ],
      "source": {
        "advisory": "GHSA-m998-r5ww-rqjf",
        "discovery": "UNKNOWN"
      },
      "title": "h2o: buffer overflow when using the %{error}x log directive"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-55368",
    "datePublished": "2026-11-04T21:38:04.613Z",
    "dateReserved": "2026-06-16T18:57:40.181Z",
    "dateUpdated": "2026-11-04T21:38:04.613Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}