Vulnerabilities in pkg:maven/io.netty/netty-handler

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-c4c3-7fpv-j4q5",
  "modified" : "2026-09-08T18:16:14Z",
  "published" : "2026-09-08T18:16:14Z",
  "aliases" : [ "CVE-2026-75595" ],
  "summary" : "Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext",
  "details" : "### Summary\nA fragmented TLS ClientHello whose handshake header spans multiple records makes Netty silently fall back to the default SslContext; where per-SNI selection is the sole mTLS gate, an unauthenticated attacker can bypass the route's mTLS requirement.\n\n### Details\nIn `io.netty.handler.ssl.SslClientHelloHandler#decode` the guard that should wait for the 4-byte handshake header checks the wrong offset - it ignores the 5-byte record header that precedes it - and therefore never fires:\n\n```java\nif (handshakeLength == -1) {\n    if (readerIndex + 4 > endOffset) {\n        // Need more data to read HandshakeType and handshakeLength (4 bytes)\n        return;\n    }\n```\n\nWhen the first record's payload is < 4 bytes, `handshakeLength = in.getUnsignedMedium(readerIndex + SslUtils.SSL_RECORD_HEADER_LENGTH + 1);` leads to `IndexOutOfBoundsException `. That is caught by the generic `catch (Exception)` block, which calls `select(ctx, null)` - this is the default `SslContext`. Fallback to default on parse failure is a problem when per-SNI selection is the sole mTLS gate.\n\n### Impact\nSNI routing bypass. Escalates to an unauthenticated mTLS bypass only when:\n- mTLS is enforced solely via per-SNI SslContext (clientAuth=REQUIRE)\n- the default/fallback SslContext is permissive (clientAuth=NONE/OPTIONAL)\n- no secondary peer-certificate verification exists at the application layer.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.netty:netty-handler"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.2.0.Final"
      }, {
        "fixed" : "4.2.17.Final"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.2.16.Final"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.netty:netty-handler"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.1.137.Final"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.1.136.Final"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/security/advisories/GHSA-c4c3-7fpv-j4q5"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-75595"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/pull/17213"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/pull/17217"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/netty/netty"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/releases/tag/netty-4.1.137.Final"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/releases/tag/netty-4.2.17.Final"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-475", "CWE-754" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-09-08T18:16:14Z",
    "nvd_published_at" : "2026-08-19T21:17:37Z"
  }
}