Express detrás de proxies

When running an Express app behind a reverse proxy, some of the Express APIs may return different values than expected. In order to adjust for this, the trust proxy application setting may be used to expose information provided by the reverse proxy in the Express APIs. The most common issue is express APIs that expose the client’s IP address may instead show an internal IP address of the reverse proxy.

When configuring the trust proxy setting, it is important to understand the exact setup of the reverse proxy. Since this setting will trust values provided in the request, it is important that the combination of the setting in Express matches how the reverse proxy operates.

The application setting trust proxy may be set to one of the values listed in the following table.

TypeValue
Booleano

Si es true, la dirección IP del cliente se entiende como la entrada más a la izquierda en la cabecera X-Forwarded-*.

Si es false, la aplicación se entiende como orientada directamente a Internet, y la dirección IP del cliente se obtiene de req.connection.remoteAddress. Este es el valor predeterminado.

When setting to true, it is important to ensure that the last reverse proxy trusted is removing/overwriting all of the following HTTP headers: X-Forwarded-For, X-Forwarded-Host, and X-Forwarded-Proto, otherwise it may be possible for the client to provide any value.
IP addresses

An IP address, subnet, or an array of IP addresses and subnets to trust as being a reverse proxy. The following list shows the pre-configured subnet names:

  • loopback - 127.0.0.1/8, ::1/128
  • linklocal - 169.254.0.0/16, fe80::/10
  • uniquelocal - 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, fc00::/7

Puede establecer direcciones IP de varias formas:

app.set('trust proxy', 'loopback') // specify a single subnet
app.set('trust proxy', 'loopback, 123.123.123.123') // specify a subnet and an address
app.set('trust proxy', 'loopback, linklocal, uniquelocal') // specify multiple subnets as CSV
app.set('trust proxy', ['loopback', 'linklocal', 'uniquelocal']) // specify multiple subnets as an array

Cuando se especifican, las direcciones IP o las subredes se excluyen del proceso de determinación de direcciones, y la dirección IP no de confianza más próxima al servidor de aplicaciones se establece como la dirección IP del cliente. This works by checking if req.socket.remoteAddress is trusted. If so, then each address in X-Forwarded-For is checked from right to left until the first non-trusted address.
Number

Use the address that is at most n number of hops away from the Express application. req.socket.remoteAddress is the first hop, and the rest are looked for in the X-Forwarded-For header from right to left. A value of 0 means that the first untrusted address would be req.socket.remoteAddress, i.e. there is no reverse proxy.

When using this setting, it is important to ensure there are not multiple, different-length paths to the Express application such that the client can be less than the configured number of hops away, otherwise it may be possible for the client to provide any value.
Function

Custom trust implementation.

app.set('trust proxy', (ip) => {
  if (ip === '127.0.0.1' || ip === '123.123.123.123') return true // trusted IPs
  else return false
})

Enabling trust proxy will have the following impact:

El valor trust proxy se implementa utilizando el paquete proxy-addr. For more information, see its documentation.

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