TLS/SSL (im_ssl)

This module uses the OpenSSL library to receive data over a secure TLS/SSL connection. It works like the TCP input module, but performs a TLS/SSL handshake at connection time and encrypts data in transit. Use this module instead of the TCP input module when you need to protect data from eavesdropping or tampering in transit.

The module populates the $raw_event core field with data received over the network. You can then process this field further, for example, by parsing it into structured data or transforming it into another format, such as JSON or XML. See Parse common event formats in the NXLog Platform User Guide for examples.

To examine the supported platforms, see the list of installation packages.

Configuration

The im_ssl module accepts the following directives in addition to the common module directives.

TLS/SSL directives

The following directives configure secure data transfer via TLS/SSL.

AllowExpired

Set this directive to TRUE to allow connections with remote hosts presenting an expired certificate. The default is FALSE; the module rejects connections with expired certificates. This directive only takes effect when RequireCert is set to TRUE.

AllowHostnameValidation

Set this directive to TRUE to require that the certificate FQDN matches the server hostname before allowing a connection. The default is FALSE; the module does not validate the remote server hostname.

AllowUntrusted

Set this directive to TRUE to allow connections with remote hosts regardless of certificate verification results. The default is FALSE; the module only accepts connections with trusted certificates.

CADir

Set this directive to the path of a directory containing Certificate Authority (CA) certificates. The module uses these certificates to verify the certificate presented by the remote host. Name the certificate files using the OpenSSL hashed format: the hash of the certificate followed by .0, .1, and so on. To find the hash of a certificate using OpenSSL:

$ openssl x509 -hash -noout -in ca.crt

For example, if the certificate hash is e2f14e4a, name the certificate file e2f14e4a.0. If there is another certificate with the same hash, name it e2f14e4a.1, and so on.

To trust a remote host’s self-signed certificate, include a copy of it in this directory.

CAFile

Set this directive to the path of the Certificate Authority (CA) certificate used to verify the certificate presented by the remote host. To trust a remote host’s self-signed certificate, specify the remote host’s certificate itself. For certificates signed by an intermediate CA, the specified certificate must contain the complete certificate chain (certificate bundle).

CAPattern

Set this directive to a PCRE2-compliant regular expression to locate a suitable Certificate Authority (CA) certificate.

This directive is supported on Windows and macOS. On Windows, the certificate must be in the Windows Certificate Store. On macOS, the certificate must be in the system keychain.

The pattern must be in the format "SUBJECT=, CN=; DN=CN=, O=, OU=, L=, ST=, C=; SAN=;". For example:

CAPattern    'DN=CN=SERVER01\.example\.com.*?SAN=DNS:SERVER01\.example\.com'

This produces the following output in the NXLog Agent log file:

matching pattern [DN=CN=SERVER01\.example\.com;.*?SAN=DNS:SERVER01\.example\.com] to certificate [SUBJECT=US, ClientState, ClientCity, ClientCompany, ClientUnit, SERVER01.example.com, CN=SERVER01.example.com; DN=CN=SERVER01.example.com, O=ClientCompany, OU=ClientUnit, L=ClientCity, ST=ClientState, C=US; SAN=DNS:SERVER01.example.com; DNS:www.SERVER01.example.com; IP:127.0.0.3; ]

If the pattern matches multiple certificates, NXLog Agent uses the first match. If the certificate changes, restart NXLog Agent to apply the new certificate.

This directive is mutually exclusive with the CAThumbprint, CADir, and CAFile directives.

On macOS, keychain behavior and certificate requirements depend on your operating system version. Newer versions enforce stricter rules on certificate algorithms and key sizes. A certificate and private key may be imported into the keychain, yet remain unusable if they do not comply with the current macOS requirements. After importing, you may also need to give NXLog Agent permission to use the certificate in the keychain.

Check your operating system documentation to find out which certificates are trusted and valid. See also Apple’s certificate requirements for macOS.

CAThumbprint

Set this directive to the thumbprint of the Certificate Authority (CA) certificate used to verify the certificate presented by the remote host.

This directive is supported on Windows and macOS. On Windows, copy the hexadecimal fingerprint string from Windows Certificate Manager (certmgr.msc). The certificate must be in a Windows certificate store accessible by NXLog Agent.

On macOS, obtain the hexadecimal fingerprint string from the Keychain Access application. The certificate must be accessible in the system keychain.

Whitespaces and colons are automatically removed.

This directive is mutually exclusive with the CADir, CAFile and CAPattern directives.

Check your operating system documentation to find out which certificates are trusted and valid. See also Apple’s certificate requirements for macOS.

CertFile

Set this directive to the path of the certificate file to present to the remote host during the TLS/SSL handshake.

CertKeyFile

Set this directive to the path of the private key file corresponding to the certificate specified by CertFile.

CertPattern

Set this directive to a PCRE2-compliant pattern to identify the certificate and its corresponding private key. The pattern must use the format "SUBJECT=, CN=, DN=, SAN=" where DN is "CN=, O=, OU=, L=, ST=, C=". This directive is supported on Windows and macOS.

On Windows, import the certificate in PFX format into the Local Computer\Personal certificate store.

On macOS, ensure the certificate and its private key are present in the System Keychain (/Library/Keychains/System.keychain).

If the pattern matches multiple certificates, NXLog Agent uses the first match. If the certificate changes, restart NXLog Agent to apply the new certificate.

This directive is mutually exclusive with the CertThumbprint, CertFile and CertKeyFile directives.

For example:

CertPattern    $hostname + 'Cert'

CertPattern    DN=CN=Client\.example\.com;.*?SAN=DNS:Client\.example\.com

This produces the following output in the NXLog Agent log file:

matching pattern [DN=CN=Client\.example\.com;.*?SAN=DNS:Client\.example\.com] to certificate [SUBJECT=US, ClientState, ClientCity, ClientCompany, ClientUnit, Client.example.com, CN=Client.example.com; DN=CN=Client.example.com, O=ClientCompany, OU=ClientUnit, L=ClientCity, ST=ClientState, C=US; SAN=DNS:Client.example.com; DNS:www.Client.example.com; IP:127.0.0.3; ]

Check your operating system documentation to find out which certificates are trusted and valid. See also Apple’s certificate requirements for macOS.

CertThumbprint

Set this directive to the thumbprint of the certificate to present to the remote server during the TLS/SSL handshake. Whitespaces and colons are automatically removed.

This directive is supported on Windows and macOS. On Windows, copy the hexadecimal fingerprint string from Windows Certificate Manager (certmgr.msc). Import the certificate to the Local Computer\Personal certificate store in PFX format. To create a PFX file from the certificate and private key using OpenSSL:

$ openssl pkcs12 -export -out server.pfx -inkey server.key -in server.pem

When the global directive UseCNGCertificates is set to FALSE, the private key must be exportable.

If you generate the certificate request using Windows Certificate Manager, enable the Make private key exportable option from the certificate properties.
If you import the certificate with the Windows Certificate Import Wizard, make sure that the Mark this key as exportable option is enabled.
If you migrate the certificate and associated private key from one Windows machine to another, select Yes, export the private key when exporting from the source machine.

When UseCNGCertificates is set to TRUE, the private key does not need to be exportable. For example, private keys stored on a TPM are always non-exportable.

On macOS, obtain the hexadecimal fingerprint string from the Keychain Access application. The certificate and its associated private key must be present in the System Keychain (/Library/Keychains/System.keychain).

For example:

CertThumbprint    7c2cc5a5fb59d4f46082a510e74df17da95e2152

This directive is mutually exclusive with the CertFile and CertKeyFile directives.

Check your operating system documentation to find out which certificates are trusted and valid. See also Apple’s certificate requirements for macOS.

CRLDir

Set this directive to the path of a directory containing certificate revocation list (CRL) files. The module uses these files to reject connections from hosts presenting a revoked certificate. Name the files using the OpenSSL hashed format: the hash of the issuer followed by .r0, .r1, and so on. To find the hash of the issuer of a CRL file using OpenSSL:

$ openssl crl -hash -noout -in crl.pem

For example, if the hash is e2f14e4a, name the file e2f14e4a.r0. If there is another file with the same hash, name it e2f14e4a.r1, and so on.

CRLFile

Set this directive to the path of the certificate revocation list (CRL) file used to reject connections from hosts presenting a revoked certificate. To generate a CRL file using OpenSSL:

$ openssl ca -gencrl -out crl.pem

DHFile

Set this directive to the path of a file containing Diffie-Hellman parameters for key exchange. Generate the parameters using dhparam(1ssl). If this directive is not set, the module uses default parameters. See the OpenSSL Wiki for further details.

KeyPass

Set this directive to the passphrase of the private key specified by CertKeyFile. This directive applies only to encrypted private keys.

To generate a private key with Triple DES encryption using OpenSSL:

$ openssl genrsa -des3 -out server.key 2048

LoadCertificateChains

Set this directive to TRUE to load the full certificate chain from the PEM file referenced by CertFile, which may contain a single certificate or the complete chain. The default is FALSE; the module loads certificates from the operating system certificate store instead.

This directive is only supported on Windows.

RequireCert

Set this directive to TRUE to require the remote host to present a certificate during the TLS/SSL handshake. The module refuses the connection if no certificate is presented. The default is TRUE.

SearchAllCertStores

Set this directive to TRUE to load all available Windows certificates into NXLog Agent for use during remote certificate verification. Any required certificates must be in a Windows certificate store accessible by NXLog Agent. This directive is only supported on Windows and is mutually exclusive with the CAThumbprint, CADir, and CAFile directives.

Sigalgs

Set this directive to the signature algorithm parameter to pass to the Windows SSL library. Accepted values depend on the available encryption providers. This directive is only supported on Windows.

SNI

Set this directive to the hostname to use for Server Name Indication (SNI).

SSLCipher

Set this directive to override the permitted cipher list for TLSv1.2 and below. Use the format described in the ciphers(1ssl) man page. For example, specify RSA:!COMPLEMENTOFALL to include all ciphers with RSA authentication but exclude ciphers without encryption.

If RSA or DSA ciphers with Diffie-Hellman key exchange are used, set DHFile to specify custom Diffie-Hellman parameters.

SSLCiphersuites

Set this directive to override the permitted cipher list for TLSv1.3. Use the same format as SSLCipher. Refer to the OpenSSL documentation for a list of valid TLS v1.3 cipher suites. The default is:

TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256:TLS_AES_128_GCM_SHA256

SSLCompression

Set this directive to TRUE to compress data using zlib when sending over the network. The default is FALSE; the module sends data without compression.

Some Linux distributions, including Debian, provide an OpenSSL library without zlib support. The module emits a warning on startup if compression support is missing. The generic deb/rpm packages are bundled with a zlib-enabled libssl library.

SSLProtocol

Set this directive to restrict the TLS/SSL protocols the module accepts. Specify a comma-separated list of the following values: SSLv2, SSLv3, TLSv1, TLSv1.1, TLSv1.2, and TLSv1.3. The default is TLSv1.2 and TLSv1.3. The OpenSSL library shipped by some Linux distributions does not support SSLv2 and SSLv3; these protocols will not work even if specified here.

TLSConnectLog

Set this directive to TRUE to log the TLS protocol version and cipher suite on each successful TLS/SSL handshake. This is useful for debugging, security audits, and verifying compliance with encryption standards.

TLSCertLog

Set this directive to TRUE to log the remote host’s certificate details during the TLS/SSL handshake. When available, the module logs the Subject, Issuer, NotBefore, and NotAfter fields to the NXLog Agent log file. The default is FALSE.

This directive depends on the values of the AllowUntrusted and RequireCert directives:

AllowUntrusted RequireCert Outcome

FALSE

Output depends on TLSCertLog value

FALSE

TRUE

Output depends on TLSCertLog value

TRUE

FALSE

No output regardless of TLSCertLog value

TRUE

Output depends on TLSCertLog value

UseCNGCertificates

Set this directive to TRUE to use the Windows Cryptography API: Next Generation (CNG) to access the private keys of certificates identified by a thumbprint. This directive is only supported on Windows.

Optional directives

InputType

This directive is identical to the InputType common module directive.

The default is LineBased, meaning the module expects CRLF as the record terminator on Windows or LF on Unix.

ListenAddr

Set this directive to the IP address or DNS hostname on which the module accepts connections. The default is localhost, which restricts access to the local machine and prevents connections from remote hosts.

Append the port number to the address using a colon separator (host:port). The default port is 514. For IPv6 addresses, enclose the address in square brackets ([addr]:port). Use 0.0.0.0:514 for IPv4 or [::]:514 for IPv6 to accept connections on all interfaces. NXLog Agent requires additional privileges to bind to ports below 1024 on Linux. See Granting additional Linux capabilities for more information.

You can specify this directive multiple times to accept connections on multiple addresses or ports within a single module instance. Set IPv4 and IPv6 addresses as separate entries. If you use a DNS name, keep the number of addresses or CNAMEs below 16 to avoid errors caused by DNS response size limits.

AllowIP

Set this directive to restrict incoming connections to specific IP addresses or networks. You can specify this directive multiple times to allow multiple IPs or networks. AllowIP has no effect unless ListenAddr is configured.

If AllowIP is not set, the module falls back to BlockIP to deny specific connections. If neither AllowIP nor BlockIP is set, the module does not restrict incoming connections.

The following IP address formats may be used:

0.0.0.0 (IPv4 address)
0.0.0.0/32 (IPv4 network with subnet bits)
0.0.0.0/0.0.0.0 (IPv4 network with subnet address)
aa::1 (IPv6 address)
aa::12/64 (IPv6 network with subnet bits)

BlockIP

Set this directive to deny incoming connections from specific IP addresses or networks. You can specify this directive multiple times to deny multiple IPs or networks. BlockIP has no effect unless ListenAddr is configured.

If BlockIP is not set, the module falls back to AllowIP to restrict incoming connections. If neither BlockIP nor AllowIP is set, the module does not restrict incoming connections.

The following IP address formats may be used:

0.0.0.0 (IPv4 address)
0.0.0.0/32 (IPv4 network with subnet bits)
0.0.0.0/0.0.0.0 (IPv4 network with subnet address)
aa::1 (IPv6 address)
aa::12/64 (IPv6 network with subnet bits)

MaxConnections

Set this directive to limit the number of concurrent active connections for a listening TCP socket. The default is 4294967295 (unlimited). When the limit is reached, the module rejects new connections and logs an error:

Number of allowed active connections(10) reached: 10. Refusing connection from 127.0.0.1

ConnectionIdleTimeout

Set this directive to close TCP connections that have been idle for longer than the specified number of seconds. The minimum value is 15 seconds. If this directive is not set, the module keeps idle TCP connections open indefinitely.

ExclusiveAddrUse

Set this directive to TRUE to prevent other processes or module instances from binding to the same port.

The default is FALSE; multiple module instances can bind to the same port.

This directive is only supported on Windows.

ReuseAddr

Set this directive to TRUE to allow the module instance to bind to a port that is already in use.

The default is TRUE; multiple module instances can listen on the same port and process data simultaneously.

ReusePort

Set this directive to TRUE to allow multiple module instances to listen on the same port. Each instance runs in a separate thread, allowing NXLog Agent to process incoming logs simultaneously.

The default is FALSE; multiple module instances cannot bind to the same port.

This directive is not supported on Windows.

Fields

The following fields are created by im_ssl.

$raw_event (type: string): The data received from the remote host.
$MessageSourceAddress (type: ipaddr): The IP address of the remote host.

Examples

Example 1. Basic im_ssl configuration

The following is a basic configuration that listens for connections on all available IPv4 network interfaces.

nxlog.conf

<Input ssl>
    Module         im_ssl
    ListenAddr     0.0.0.0:514
    CAFile         %CERTDIR%/ca.pem (1)
    CertFile       %CERTDIR%/agent-cert.pem (2)
    CertKeyFile    %CERTDIR%/agent-key.pem (3)
    KeyPass        secret (4)
</Input>

1	The CAFile directive specifies the path of the Certificate Authority (CA) certificate.
2	The CertFile directive specifies the path of the local server’s certificate.
3	The CertKeyFile directive specifies the path of the server’s certificate private key.
4	If the private key is encrypted, specify the password in the KeyPass directive.