CVE-2026-40396

{
  "id": "CVE-2026-40396",
  "sourceIdentifier": "[email protected]",
  "published": "2026-04-12T20:16:19.057",
  "lastModified": "2026-10-26T21:10:00.170",
  "vulnStatus": "Analyzed",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Varnish Cache 9 before 9.0.1 allows a \"workspace overflow\" denial of service (daemon panic) after timeout_linger. A malicious client could send an HTTP/1 request, wait long enough until the session releases its worker thread (timeout_linger) and resume traffic before the session is closed (timeout_idle) sending more than one request at once to trigger a pipelining operation between requests. This vulnerability affecting Varnish Cache 9.0.0 emerged from a port of the Varnish Enterprise non-blocking architecture for HTTP/2. New code was needed to adapt to a more recent workspace API that formalizes the pipelining operation. In addition to the workspace change on the Varnish Cache side, other differences created merge conflicts, like partial support for trailers in Varnish Enterprise. The conflict resolution missed one code path configuring pipelining to perform a complete workspace rollback, losing the guarantee that prefetched data would fit inside workspace_client during the transition from one request to the next. This can result in a workspace overflow, triggering a panic and crashing the Varnish server."
    },
    {
      "lang": "es",
      "value": "Varnish Cache 9 anterior a la 9.0.1 permite una ’sobrecarga de espacio de trabajo’ (workspace overflow) denegación de servicio (pánico del demonio) después de timeout_linger. Un cliente malicioso podría enviar una solicitud HTTP/1, esperar el tiempo suficiente hasta que la sesión libere su hilo de trabajo (timeout_linger) y reanudar el tráfico antes de que la sesión se cierre (timeout_idle) enviando más de una solicitud a la vez para activar una operación de pipelining entre solicitudes. Esta vulnerabilidad que afecta a Varnish Cache 9.0.0 surgió de una adaptación de la arquitectura no bloqueante de Varnish Enterprise para HTTP/2. Se necesitó código nuevo para adaptarse a una API de espacio de trabajo más reciente que formaliza la operación de pipelining. Además del cambio en el espacio de trabajo por parte de Varnish Cache, otras diferencias crearon conflictos de fusión, como el soporte parcial para trailers en Varnish Enterprise. La resolución de conflictos omitió una ruta de código que configuraba el pipelining para realizar una reversión completa del espacio de trabajo, perdiendo la garantía de que los datos precargados cabrían dentro de workspace_client durante la transición de una solicitud a la siguiente. Esto puede resultar en una sobrecarga del espacio de trabajo (workspace overflow), lo que desencadena un pánico y provoca la caída del servidor Varnish."
    }
  ],
  "affected": [
    {
      "source": "[email protected]",
      "affectedData": [
        {
          "vendor": "varnish-software",
          "product": "Varnish Cache",
          "defaultStatus": "unaffected",
          "versions": [
            {
              "version": "9.0.0",
              "lessThan": "9.0.1",
              "versionType": "semver",
              "status": "affected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {
    "cvssMetricV31": [
      {
        "source": "[email protected]",
        "type": "Secondary",
        "cvssData": {
          "version": "3.1",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:L",
          "baseScore": 4.0,
          "baseSeverity": "MEDIUM",
          "attackVector": "NETWORK",
          "attackComplexity": "HIGH",
          "privilegesRequired": "NONE",
          "userInteraction": "NONE",
          "scope": "CHANGED",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "availabilityImpact": "LOW"
        },
        "exploitabilityScore": 2.2,
        "impactScore": 1.4
      },
      {
        "source": "[email protected]",
        "type": "Primary",
        "cvssData": {
          "version": "3.1",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
          "baseScore": 7.5,
          "baseSeverity": "HIGH",
          "attackVector": "NETWORK",
          "attackComplexity": "LOW",
          "privilegesRequired": "NONE",
          "userInteraction": "NONE",
          "scope": "UNCHANGED",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "availabilityImpact": "HIGH"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 3.6
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "timestamp": "2026-04-13T15:35:30.690667Z",
          "id": "CVE-2026-40396",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
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              "technicalImpact": "partial"
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          "role": "CISA Coordinator",
          "version": "2.0.3"
        }
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  },
  "weaknesses": [
    {
      "source": "[email protected]",
      "type": "Secondary",
      "description": [
        {
          "lang": "en",
          "value": "CWE-670"
        }
      ]
    }
  ],
  "configurations": [
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  "references": [
    {
      "url": "https://github.com/varnish/varnish/issues/15",
      "source": "[email protected]",
      "tags": [
        "Issue Tracking"
      ]
    },
    {
      "url": "https://github.com/varnish/varnish/releases/tag/varnish-9.0.1",
      "source": "[email protected]",
      "tags": [
        "Product"
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    }
  ]
}