{"id":"CVE-2026-75595","state":"PUBLISHED","title":"Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext","description":"Netty is an asynchronous, event-driven network application framework. Prior to 4.1.137.Fina and 4.2.17.Final, io.netty.handler.ssl.SslClientHelloHandler#decode checks the wrong offset before reading the four-byte TLS handshake header, so a ClientHello whose handshake header spans records can cause an IndexOutOfBoundsException and invoke select(ctx, null). This selects the default SslContext instead of the SNI-specific context. In deployments where per-SNI clientAuth=REQUIRE is the sole mutual TLS gate, the default SslContext uses clientAuth=NONE or clientAuth=OPTIONAL, and no application-layer certificate verification exists, an unauthenticated remote attacker can bypass the protected route's mutual TLS requirement. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final.","publishedAt":"2026-08-19T21:00:27.627Z","updatedAt":"2026-08-20T14:06:16.963Z","severity":{"score":9.1,"label":"Critical","version":"4.0","vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N","source":"GitHub_M"},"assigner":"GitHub_M","products":["netty netty"],"affected":[{"vendor":"netty","product":"netty","versions":[{"version":"< 4.1.137.Final","status":"affected"},{"version":">= 4.2.0.Final, < 4.2.17.Final","status":"affected"}]}],"references":["https://github.com/netty/netty/security/advisories/GHSA-c4c3-7fpv-j4q5","https://github.com/netty/netty/pull/17213","https://github.com/netty/netty/pull/17217","https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7","https://github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961","https://github.com/netty/netty/releases/tag/netty-4.1.137.Final","https://github.com/netty/netty/releases/tag/netty-4.2.17.Final"],"weaknesses":["CWE-754"],"ingestedAt":"2026-10-29T20:12:58.252Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/75xxx/CVE-2026-75595.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-75595","state":"PUBLISHED","datePublished":"2026-08-19T21:00:27.627Z","dateUpdated":"2026-08-20T14:06:16.963Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-08-17T23:49:03.449Z"},"containers":{"cna":{"title":"Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext","descriptions":[{"lang":"en","value":"Netty is an asynchronous, event-driven network application framework. Prior to 4.1.137.Fina and 4.2.17.Final, io.netty.handler.ssl.SslClientHelloHandler#decode checks the wrong offset before reading the four-byte TLS handshake header, so a ClientHello whose handshake header spans records can cause an IndexOutOfBoundsException and invoke select(ctx, null). This selects the default SslContext instead of the SNI-specific context. In deployments where per-SNI clientAuth=REQUIRE is the sole mutual TLS gate, the default SslContext uses clientAuth=NONE or clientAuth=OPTIONAL, and no application-layer certificate verification exists, an unauthenticated remote attacker can bypass the protected route's mutual TLS requirement. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final."}],"affected":[{"vendor":"netty","product":"netty","versions":[{"version":"< 4.1.137.Final","status":"affected"},{"version":">= 4.2.0.Final, < 4.2.17.Final","status":"affected"}]}],"references":[{"url":"https://github.com/netty/netty/security/advisories/GHSA-c4c3-7fpv-j4q5","name":"https://github.com/netty/netty/security/advisories/GHSA-c4c3-7fpv-j4q5","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/netty/netty/pull/17213","name":"https://github.com/netty/netty/pull/17213","tags":["x_refsource_MISC"]},{"url":"https://github.com/netty/netty/pull/17217","name":"https://github.com/netty/netty/pull/17217","tags":["x_refsource_MISC"]},{"url":"https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7","name":"https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7","tags":["x_refsource_MISC"]},{"url":"https://github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961","name":"https://github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961","tags":["x_refsource_MISC"]},{"url":"https://github.com/netty/netty/releases/tag/netty-4.1.137.Final","name":"https://github.com/netty/netty/releases/tag/netty-4.1.137.Final","tags":["x_refsource_MISC"]},{"url":"https://github.com/netty/netty/releases/tag/netty-4.2.17.Final","name":"https://github.com/netty/netty/releases/tag/netty-4.2.17.Final","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV4_0":{"attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"PRESENT","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"HIGH","vulnIntegrityImpact":"HIGH","vulnAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","subAvailabilityImpact":"NONE","baseScore":9.1,"baseSeverity":"CRITICAL","vectorString":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N","version":"4.0"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-754","lang":"en","description":"CWE-754: Improper Check for Unusual or Exceptional Conditions","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-08-19T21:00:27.627Z"},"source":{"advisory":"GHSA-c4c3-7fpv-j4q5","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-20T14:05:51.091097Z","id":"CVE-2026-75595","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-08-20T14:06:16.963Z"}}]}}}