CVE-2026-40395
Full vulnerability record from the local CVENow database.
Description
Varnish Enterprise before 6.0.16r12 allows a "workspace overflow" denial of service (daemon panic) for shared VCL. The headerplus.write_req0() function from vmod_headerplus updates the underlying req0, which is normally the original read-only request from which req is derived (readable and writable from VCL). This is useful in the active VCL, after amending req, to prepare a refined req0 before switching to a different VCL with the return (vcl(<label>)) action. This is for example how the Varnish Controller operates shared VCL deployments. If the amended req contained too many header fields for req0, this would have resulted in a workspace overflow that would in turn trigger a panic and crash the Varnish Enterprise server. This could be used as a Denial of Service attack vector by malicious clients.
Severity
HIGH
CVSS score
7.5
(v3.1)
Vulnerability status
Analyzed
Source identifier
Published
2026-04-12 20:16:18.893000
Last modified
2026-10-26 22:10:00.163000
View original CVE JSON
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"sourceIdentifier": "[email protected]",
"published": "2026-04-12T20:16:18.893",
"lastModified": "2026-10-26T22:10:00.163",
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},
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"value": "Varnish Enterprise anterior a 6.0.16r12 permite una ’desbordamiento de espacio de trabajo’ denegación de servicio (pánico del demonio) para VCL compartido. La función headerplus.write_req0() de vmod_headerplus actualiza el req0 subyacente, que normalmente es la solicitud original de solo lectura de la cual se deriva req (legible y escribible desde VCL). Esto es útil en el VCL activo, después de modificar req, para preparar un req0 refinado antes de cambiar a un VCL diferente con la acción return (vcl([label])). Así es, por ejemplo, como el Varnish Controller opera las implementaciones de VCL compartido. Si el req modificado contenía demasiados campos de encabezado para req0, esto habría resultado en un desbordamiento de espacio de trabajo que a su vez desencadenaría un pánico y colapsaría el servidor Varnish Enterprise. Esto podría usarse como un vector de ataque de denegación de servicio por clientes maliciosos."
}
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"affected": [
{
"source": "[email protected]",
"affectedData": [
{
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"product": "Varnish Enterprise",
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"references": [
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"source": "[email protected]",
"tags": [
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}