CVE-2026-75595 (GCVE-0-2026-75595)

Vulnerability from cvelistv5 – Published: 2026-08-19 21:00 – Updated: 2026-08-19 21:00
VLAI
Title
Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext
Summary
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.
Severity
9.1 (Critical)
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
CWE
  • CWE-754 - Improper Check for Unusual or Exceptional Conditions
Assigner
References
Impacted products
Vendor Product Version CPE status
netty netty Affected: < 4.1.137.Final
Affected: >= 4.2.0.Final, < 4.2.17.Final
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{
  "containers": {
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      "affected": [
        {
          "product": "netty",
          "vendor": "netty",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 4.1.137.Final"
            },
            {
              "status": "affected",
              "version": "\u003e= 4.2.0.Final, \u003c 4.2.17.Final"
            }
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      ],
      "descriptions": [
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          "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\u0027s mutual TLS requirement. This issue is fixed in versions 4.1.137.Final and 4.2.17.Final."
        }
      ],
      "metrics": [
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            "attackComplexity": "LOW",
            "attackRequirements": "PRESENT",
            "attackVector": "NETWORK",
            "baseScore": 9.1,
            "baseSeverity": "CRITICAL",
            "privilegesRequired": "NONE",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "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",
            "vulnAvailabilityImpact": "NONE",
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            "vulnIntegrityImpact": "HIGH"
          }
        }
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            }
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      "providerMetadata": {
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        "shortName": "GitHub_M"
      },
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          "tags": [
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          "url": "https://github.com/netty/netty/pull/17217"
        },
        {
          "name": "https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7",
          "tags": [
            "x_refsource_MISC"
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          "url": "https://github.com/netty/netty/commit/1b5abc6443b63726c72cdd285af2feb7ddbb8ff7"
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          "tags": [
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          ],
          "url": "https://github.com/netty/netty/commit/9e0519239108a69b7e9bbc5e9182ee139a0d7961"
        },
        {
          "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-4.1.137.Final"
        },
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          "name": "https://github.com/netty/netty/releases/tag/netty-4.2.17.Final",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/netty/netty/releases/tag/netty-4.2.17.Final"
        }
      ],
      "source": {
        "advisory": "GHSA-c4c3-7fpv-j4q5",
        "discovery": "UNKNOWN"
      },
      "title": "Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-75595",
    "datePublished": "2026-08-19T21:00:27.627Z",
    "dateReserved": "2026-08-17T23:49:03.449Z",
    "dateUpdated": "2026-08-19T21:00:27.627Z",
    "state": "PUBLISHED"
  },
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  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-75595",
      "date": "2026-08-20",
      "epss": "0.00317",
      "percentile": "0.2465"
    },
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  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
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  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


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