FKIE_CVE-2026-55996

Vulnerability from fkie_nvd - Published: 2026-08-05 08:16 - Updated: 2026-10-24 16:10
Severity
4.3 (Medium) - CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Summary
A denial-of-service vulnerability was identified in multiple TLS listeners in Rancher. Both the cattle-cluster-agent component running in downstream clusters and the Rancher server itself use the dynamiclistener library to serve TLS traffic. Without an effective CN filter configured, dynamiclistener automatically appended to each serving certificate any hostname presented via Server Name Indication (SNI) in incoming TLS requests. An unauthenticated attacker with network access within the affected cluster could send a large number of TLS requests with distinct hostnames, causing the serving certificate to accumulate an unbounded number of Subject Alternative Names (SANs). Eventually, the certificate grows large enough that TLS handshakes fail with an excessive message size error, causing a denial of service on the affected listeners.
References
meissner@suse.dehttps://bugzilla.suse.com/show_bug.cgi?id=CVE-2026-55996
meissner@suse.dehttps://github.com/rancher/rancher/security/advisories/GHSA-9jxv-832x-45q9
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "packageName": "Rancher",
          "product": "Rancher",
          "vendor": "SUSE",
          "versions": [
            {
              "lessThan": "2.11.16",
              "status": "affected",
              "version": "2.11.0",
              "versionType": "semver"
            },
            {
              "lessThan": "2.12.12",
              "status": "affected",
              "version": "2.12.0",
              "versionType": "semver"
            },
            {
              "lessThan": "2.13.8",
              "status": "affected",
              "version": "2.13.0",
              "versionType": "semver"
            },
            {
              "lessThan": "2.14.4",
              "status": "affected",
              "version": "2.14.0",
              "versionType": "semver"
            }
          ]
        }
      ],
      "source": "meissner@suse.de"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "A denial-of-service vulnerability was identified in multiple TLS listeners in Rancher. Both the cattle-cluster-agent component running in downstream clusters and the Rancher server itself use the dynamiclistener library to serve TLS traffic. Without an effective CN filter configured, dynamiclistener automatically appended to each serving certificate any hostname presented via Server Name Indication (SNI) in incoming TLS requests.\n\n\n\nAn unauthenticated attacker with network access within the affected cluster could send a large number of TLS requests with distinct hostnames, causing the serving certificate to accumulate an unbounded number of Subject Alternative Names (SANs). Eventually, the certificate grows large enough that TLS handshakes fail with an excessive message size error, causing a denial of service on the affected listeners."
    },
    {
      "lang": "es",
      "value": "Una vulnerabilidad de denegaci\u00f3n de servicio fue identificada en m\u00faltiples oyentes TLS en Rancher. Tanto el componente cattle-cluster-agent ejecut\u00e1ndose en cl\u00fasteres descendentes como el propio servidor de Rancher utilizan la biblioteca dynamiclistener para servir tr\u00e1fico TLS. Sin un filtro CN efectivo configurado, dynamiclistener a\u00f1adi\u00f3 autom\u00e1ticamente a cada certificado de servicio cualquier nombre de host presentado a trav\u00e9s de Server Name Indication (SNI) en las solicitudes TLS entrantes.\n\nUn atacante no autenticado con acceso de red dentro del cl\u00faster afectado podr\u00eda enviar un gran n\u00famero de solicitudes TLS con nombres de host distintos, haciendo que el certificado de servicio acumule un n\u00famero ilimitado de Subject Alternative Names (SANs). Finalmente, el certificado crece lo suficiente como para que los handshakes TLS fallen con un error de tama\u00f1o de mensaje excesivo, causando una denegaci\u00f3n de servicio en los oyentes afectados."
    }
  ],
  "id": "CVE-2026-55996",
  "lastModified": "2026-10-24T16:10:00.153",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "LOW",
          "baseScore": 4.3,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L",
          "version": "3.1"
        },
        "exploitabilityScore": 2.8,
        "impactScore": 1.4,
        "source": "meissner@suse.de",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-55996",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-08-05T13:40:18.178968Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-08-05T08:16:34.173",
  "references": [
    {
      "source": "meissner@suse.de",
      "url": "https://bugzilla.suse.com/show_bug.cgi?id=CVE-2026-55996"
    },
    {
      "source": "meissner@suse.de",
      "url": "https://github.com/rancher/rancher/security/advisories/GHSA-9jxv-832x-45q9"
    }
  ],
  "sourceIdentifier": "meissner@suse.de",
  "vulnStatus": "Awaiting Analysis",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-770"
        }
      ],
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "type": "Secondary"
    }
  ]
}



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