{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-55368", "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa", "state": "PUBLISHED", "assignerShortName": "GitHub_M", "dateReserved": "2026-06-16T18:57:40.181Z", "datePublished": "2026-11-04T21:38:04.613Z", "dateUpdated": "2026-11-04T21:38:04.613Z"}, "containers": {"cna": {"title": "h2o: buffer overflow when using the %{error}x log directive", "problemTypes": [{"descriptions": [{"cweId": "CWE-787", "lang": "en", "description": "CWE-787: Out-of-bounds Write", "type": "CWE"}]}], "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"}}], "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"}], "affected": [{"vendor": "h2o", "product": "h2o", "versions": [{"version": "< 48b7ae12107fd2b118e4641da49599e9aac8edd8", "status": "affected"}]}], "providerMetadata": {"orgId": "a0819718-46f1-4df5-94e2-005712e83aaa", "shortName": "GitHub_M", "dateUpdated": "2026-11-04T21:38:04.613Z"}, "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'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."}], "source": {"advisory": "GHSA-m998-r5ww-rqjf", "discovery": "UNKNOWN"}}}}

{}

{"affected": [{"affectedData": [{"product": "h2o", "vendor": "h2o", "versions": [{"status": "affected", "version": "< 48b7ae12107fd2b118e4641da49599e9aac8edd8"}]}], "source": "security-advisories@github.com"}], "cveTags": [], "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'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."}], "id": "CVE-2026-55368", "lastModified": "2026-11-04T22:18:06.343", "metrics": {"cvssMetricV31": [{"cvssData": {"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"}, "exploitabilityScore": 2.2, "impactScore": 5.9, "source": "security-advisories@github.com", "type": "Secondary"}]}, "published": "2026-11-04T22:18:06.343", "references": [{"source": "security-advisories@github.com", "url": "https://github.com/h2o/h2o/commit/48b7ae12107fd2b118e4641da49599e9aac8edd8"}, {"source": "security-advisories@github.com", "url": "https://github.com/h2o/h2o/pull/3757"}, {"source": "security-advisories@github.com", "url": "https://github.com/h2o/h2o/security/advisories/GHSA-m998-r5ww-rqjf"}], "sourceIdentifier": "security-advisories@github.com", "vulnStatus": "Received", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-787"}], "source": "security-advisories@github.com", "type": "Primary"}]}

{}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "generic", "value": "[0,48b7ae12107fd2b118e4641da49599e9aac8edd8)"}}], "enrichment": {"confidence": 100.0, "confidence_source": "matching", "scores": [{"score": 100.0, "source": "matching"}]}, "original": {"product": "h2o", "source": "cna", "vendor": "h2o"}, "product": "h2o", "vendor": "h2o"}], "created": "2026-11-04T23:15:15.781949+00:00", "updated": "2026-11-04T23:15:16.370572+00:00", "vendors": ["h2o", "h2o$PRODUCT$h2o"]}