Microsoft Azure Sentinel (om_azure)

This module forwards logs to Azure services that support the Azure Monitor HTTP Data Collector API. It has been tested with Azure Log Analytics Workspace and Azure Sentinel. It will connect to the URL specified in the configuration in either plain HTTP or HTTPS mode. Event data is sent in batches, reducing the latency caused by the HTTP responses, thus improving Microsoft Azure’s server performance.

Output log format

om_azure forwards log records over HTTP(S) as JSON payload. The JSON format depends on the value of the $raw_event field. The module checks if the value of $raw_event is valid JSON and applies the following rules:

  • If it is valid JSON, the value is forwarded as is.

  • If it is not valid JSON, the log record is converted to JSON in the following format:

    {
      "raw_event": "<json_escaped_raw_event>"
    }

Additional metadata, including the NXLog-specific fields EventReceivedTime, SourceModuleName, and SourceModuleType, will not be included in the output unless these values have been written to the $raw_event field. The processing required to achieve this depends on the format of the input data, but generally it means you need to:

  1. Parse the log record according to the data format.

    • If the input data is already in JSON format, use parse_json() to parse $raw_event into fields.

    • If the input is unstructured plain text data, copy the value of $raw_event to a custom field.

  2. Create and populate any additional custom fields.

  3. Use to_json() to convert the fields to JSON format and update the value of $raw_event.

See the Examples section for NXLog configuration examples of the above.

Configuration

The om_azure module accepts the following directives in addition to the common module directives. The SharedKey, TableName, WorkspaceID and URL directives are required.

SharedKey

This mandatory directive specifies the either the Primary key or the Secondary key (referred to as the shared key in most of the code examples in the Authorization section of the HTTP Data Collector API) of the Microsoft Azure Sentinel.

TableName

This mandatory directive specifies the name of Custom Table to which module will be sending log messages. Azure automatically appends _CL to all Custom Tables thus the table will appear as TableName_CL in the list of Custom Tables. It must be a string type expression. If the expression in the TableName directive is not a constant string (it contains functions, field names, or operators), it will be evaluated for each event.

WorkspaceID

This mandatory directive specifies the Workspace ID of the Microsoft Azure Sentinel.

URL

This mandatory directive specifies the URL for the module to POST the event data. If multiple URL directives are specified on new lines, the module works in a failover configuration. If a destination becomes unavailable, the module automatically fails over to the next one. If the last destination becomes unavailable, the module fails over to the first destination.

The module operates in plain HTTP or HTTPS mode depending on the URL provided. If the port number is not explicitly defined in the URL, it defaults to port 80 for HTTP and port 443 for HTTPS.


AddHeader

This optional directive specifies an additional header to be added to each HTTP request.

HttpBasicAuthUser

HTTP basic authorization username.

HttpBasicAuthPassword

HTTP basic authorization password.

HTTP authorization works only when both parameters are set.
HTTPSAllowExpired

This boolean directive specifies whether the connection should be allowed with an expired certificate. If set to TRUE, the connection will be allowed even if the remote server presents an expired certificate. The default is FALSE: the remote server must present a certificate that is not expired.

HTTPSAllowUntrusted

This boolean directive specifies that the connection should be allowed regardless of the certificate verification results. If set to TRUE, the connection will be allowed with any unexpired certificate provided by a server. The default value is FALSE: the remote server must present a trusted certificate.

HTTPSCADir

This directive specifies a path to a directory containing certificate authority (CA) certificates. These certificates will be used to verify the certificate presented by the remote server. The certificate files must be named using the OpenSSL hashed format, i.e. the hash of the certificate followed by .0, .1 etc. To find the hash of a certificate using OpenSSL:

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

For example if the certificate hash is e2f14e4a, then the certificate filename should be e2f14e4a.0. If there is another certificate with the same hash then it should be named e2f14e4a.1 and so on.

A remote server’s self-signed certificate (which is not signed by a CA) can also be trusted by including a copy of the certificate in this directory.

HTTPSCAFile

This specifies the path of the certificate authority (CA) certificate that will be used to verify the certificate presented by the remote server. A remote server’s self-signed certificate (which is not signed by a CA) can be trusted by specifying the remote server certificate itself. In case of certificates signed by an intermediate CA, the certificate specified must contain the complete certificate chain (certificate bundle).

HTTPSCAThumbprint

This optional directive specifies the thumbprint of the certificate authority (CA) certificate that will be used to verify the certificate presented by the remote server. The hexadecimal fingerprint string can be copied from Windows Certificate Manager (certmgr.msc). Whitespaces are automatically removed. The certificate must be added to a Windows certificate store that is accessible by NXLog. This directive is only supported on Windows and is mutually exclusive with the HTTPSCADir and HTTPSCAFile directives.

HTTPSSearchAllCertStores

This optional boolean directive, when set to TRUE, enables the loading of all available Windows certificates into NXLog, for use during remote certificate verification. Any required certificates must be added to a Windows certificate store that NXLog can access. This directive is mutual exclusive with the HTTPSCAThumbprint, HTTPSCADir and HTTPSCAFile directives.

HTTPSCertFile

This specifies the path of the certificate file that will be presented to the remote server during the HTTPS handshake.

HTTPSCertKeyFile

This specifies the path of the private key file that was used to generate the certificate specified by the HTTPSCertFile directive. This is used for the HTTPS handshake.

HTTPSCertThumbprint

This optional directive specifies the thumbprint of the certificate that will be presented to the remote server during the HTTPS handshake. The hexadecimal fingerprint string can be copied from Windows Certificate Manager (certmgr.msc). Whitespaces are automatically removed. The certificate must be imported to the Local Computer\Personal certificate store in PFX format for NXLog to find it. 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

This directive is only supported on Windows and is mutually exclusive with the HTTPSCertFile and HTTPSCertKeyFile directives.

HTTPSCRLDir

This directive specifies a path to a directory containing certificate revocation list (CRL) files. These CRL files will be used to check for certificates that were revoked and should no longer be accepted. The files must be named using the OpenSSL hashed format, i.e. the hash of the issuer followed by .r0, .r1 etc. 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, then the filename should be e2f14e4a.r0. If there is another file with the same hash then it should be named e2f14e4a.r1 and so on.

HTTPSCRLFile

This specifies the path of the certificate revocation list (CRL) which will be used to check for certificates that have been revoked and should no longer be accepted. Example to generate a CRL file using OpenSSL:

$ openssl ca -gencrl -out crl.pem
HTTPSDHFile

This optional directive specifies file with dh-parameters for Diffie-Hellman key exchange. These parameters can be generated with dhparam(1ssl). If no directive is specified, default parameters will be used. See OpenSSL Wiki for further details.

HTTPSKeyPass

This directive specifies the passphrase of the private key specified by the HTTPSCertKeyFile directive. A passphrase is required when the private key is encrypted. Example to generate a private key with Triple DES encryption using OpenSSL:

$ openssl genrsa -des3 -out server.key 2048

This directive is not needed for passwordless private keys.

HTTPSSSLCipher

This optional directive can be used to set the permitted SSL cipher list, overriding the default. Use the format described in the ciphers(1ssl) man page. For example specify RSA:!COMPLEMENTOFALL to include all ciphers with RSA authentication but leave out ciphers without encryption.

If RSA or DSA ciphers with Diffie-Hellman key exchange are used, DHFile can be set for specifying custom dh-parameters.
HTTPSSSLCiphersuites

This optional directive can be used to set the permitted cipher list for TLSv1.3. Use the same format as in the HTTPSSSLCipher directive. Refer to the OpenSSL documentation for a list of valid TLS v1.3 cipher suites. The default value is:

TLS_AES_256_GCM_SHA384:TLS_CHACHA20_POLY1305_SHA256:TLS_AES_128_GCM_SHA256
HTTPSSSLCompression

This boolean directive allows you to enable data compression when sending data over the network. The compression mechanism is based on the zlib compression library. If the directive is not specified, it defaults to FALSE: compression is disabled.

Some Linux packages (for example, Debian) use the OpenSSL library provided by the OS and may not support the zlib compression mechanism. The module will emit a warning on startup if the compression support is missing. The generic deb/rpm packages are bundled with a zlib-enabled libssl library.
HTTPSSSLProtocol

This directive can be used to set the allowed SSL/TLS protocol(s). It takes a comma-separated list of values which can be any of the following: SSLv2, SSLv3, TLSv1, TLSv1.1, TLSv1.2 and TLSv1.3. By default, the TLSv1.2 and TLSv1.3 protocols are allowed. Note that the OpenSSL library shipped by Linux distributions may not support SSLv2 and SSLv3, and these will not work even if enabled with this directive.

LocalPort

This optional directive specifies the local port number of the connection. If this is not specified, a random high port number will be used, which is not always ideal in firewalled network environments.

Due to the required TIME-WAIT delay in closing connections, attempts to bind to LocalPort may fail. In such cases, the message Address already in use will be written to nxlog.log. If the situation persists, it could impede network performance.

Proxy

This optional directive is used to specify the IP address (or hostname) and port number of the HTTP proxy server to be used. The format is hostname:port. If the port number is ommited, it defaults to 80.

The om_azure module supports HTTP proxying only. SOCKS4/SOCKS5 proxying is not supported.
Reconnect

This optional directive sets the reconnect interval in seconds. If it is set, the module attempts to reconnect in every defined second. If it is not set, the reconnect interval will start at 1 second and doubles on every attempt. If the duration of the successful connection is greater than the current reconnect interval, then the reconnect interval will be reset to 1 sec.

Procedures

The following procedures are exported by om_azure.

add_http_header(string name, string value);

Dynamically add a custom HTTP header to HTTP requests.

reconnect();

Force a reconnection. This can be used from a Schedule block to periodically reconnect to the server.

Examples

Example 1. Sending unstructured plain text logs over HTTPS

This configuration reads log messages from file and forwards them via HTTPS. No further processing is done on the log records.

nxlog.conf
<Input file>
    Module            im_file
    File              'log.txt'
</Input>

define WORKSPACE      DUMMY_WORKSPACE
define SHAREDKEY      DUMMY_SHAREDKEY

define SUBDOMAIN      ods.opinsights.azure.com
define RESOURCE       api/logs
define APIVER         api-version=2016-04-01

<Output azure>
    Module            om_azure
    URL               https://%WORKSPACE%.%SUBDOMAIN%/%RESOURCE%?%APIVER%

    WorkspaceID       %WORKSPACE%
    SharedKey         %SHAREDKEY%
    TableName         "CustomLogs"

    HTTPSCAFile       %CERTDIR%/ca.pem

    AddHeader         X-Custom  :  custom-value
    Exec              add_http_header("Y-Dynamic", "dynamic value");
</Output>
Input sample

The following is a log record sample read by NXLog.

Mar 24 15:58:53 pc1 systemd[1452]: tracker-store.service: Succeeded.
Output sample

The following is the JSON-formatted log record that will be sent to Microsoft Azure.

{
  "raw_event": "Mar 24 15:58:53 pc1 systemd[1452]: tracker-store.service: Succeeded."
}
Example 2. Sending plain text logs with metadata

This configuration reads log records from file and adds a $Hostname metadata field. Log records are converted to JSON using the to_json() procedure of the xm_json module before they are forwarded to Microsoft Azure.

nxlog.conf
<Extension json>
    Module          xm_json
</Extension>

<Input file>
    Module          im_file
    File            '/path/to/log/file'
    Exec            $Hostname = hostname();
    Exec            $Message = $raw_event;
</Input>

define WORKSPACE    DUMMY_WORKSPACE
define SHAREDKEY    DUMMY_SHAREDKEY

define SUBDOMAIN    ods.opinsights.azure.com
define RESOURCE     api/logs
define APIVER       api-version=2016-04-01

<Output azure>
    Module          om_azure
    URL             https://%WORKSPACE%.%SUBDOMAIN%/%RESOURCE%?%APIVER%
    HTTPSCAFile     %CERTDIR%/ca.pem
    WorkspaceID     %WORKSPACE%
    SharedKey       %SHAREDKEY%
    TableName       "testImFileNative_dir"
    Exec            to_json();
</Output>
Input sample

The following is a log record sample read by NXLog.

Mar 24 15:58:53 pc1 systemd[1452]: tracker-store.service: Succeeded.
Output sample

The following is the JSON-formatted log record that will be sent to Microsoft Azure.

{
  "EventReceivedTime": "2021-03-24T16:52:20.457348+01:00",
  "SourceModuleName": "file",
  "SourceModuleType": "im_file",
  "Hostname": "pc1",
  "Message": "Mar 24 15:58:53 pc1 systemd[1452]: tracker-store.service: Succeeded."
}
Example 3. Sending structured syslog records

This configuration reads syslog records from file. It uses the parse_syslog() procedure of the xm_syslog module to parse logs into structured data. Log records are then converted to JSON using the to_json() procedure of the xm_json module before they are forwarded to Microsoft Azure.

nxlog.conf
<Extension syslog>
    Module          xm_syslog
</Extension>

<Extension json>
    Module          xm_json
</Extension>

<Input file>
    Module          im_file
    File            '/path/to/log/file'
    Exec            parse_syslog();
</Input>

define WORKSPACE    DUMMY_WORKSPACE
define SHAREDKEY    DUMMY_SHAREDKEY

define SUBDOMAIN    ods.opinsights.azure.com
define RESOURCE     api/logs
define APIVER       api-version=2016-04-01

<Output azure>
    Module          om_azure
    URL             https://%WORKSPACE%.%SUBDOMAIN%/%RESOURCE%?%APIVER%
    HTTPSCAFile     %CERTDIR%/ca.pem
    WorkspaceID     %WORKSPACE%
    SharedKey       %SHAREDKEY%
    TableName       "testImFileNative_dir"
    Exec            to_json();
</Output>
Input sample

The following is a log record sample read by NXLog.

Mar 24 15:58:53 pc1 systemd[1452]: tracker-store.service: Succeeded.
Output sample

The following is the JSON-formatted log record that will be sent to Microsoft Azure.

{
  "EventReceivedTime": "2021-03-24T16:30:18.920342+01:00",
  "SourceModuleName": "file",
  "SourceModuleType": "im_file",
  "SyslogFacilityValue": 1,
  "SyslogFacility": "USER",
  "SyslogSeverityValue": 5,
  "SyslogSeverity": "NOTICE",
  "SeverityValue": 2,
  "Severity": "INFO",
  "Hostname": "pc1",
  "EventTime": "2021-03-24T15:58:53.000000+01:00",
  "SourceName": "systemd",
  "ProcessID": 1452,
  "Message": "tracker-store.service: Succeeded."
}
Example 4. Sending JSON-formatted logs with metadata

This configuration reads JSON-formatted log records from file. It uses the parse_json() procedure of the xm_json module to parse logs into structured data and adds an $EventType metadata field. Log records are then converted back to JSON using the to_json()procedure before they are forwarded to Microsoft Azure.

nxlog.conf
<Extension json>
    Module          xm_json
</Extension>

<Input file>
    Module          im_file
    File            '/path/to/log/file'
    Exec            parse_json();
    Exec            $EventType = "browser-history";
</Input>

define WORKSPACE    DUMMY_WORKSPACE
define SHAREDKEY    DUMMY_SHAREDKEY

define SUBDOMAIN    ods.opinsights.azure.com
define RESOURCE     api/logs
define APIVER       api-version=2016-04-01

<Output azure>
    Module          om_azure
    URL             https://%WORKSPACE%.%SUBDOMAIN%/%RESOURCE%?%APIVER%
    HTTPSCAFile     %CERTDIR%/ca.pem
    WorkspaceID     %WORKSPACE%
    SharedKey       %SHAREDKEY%
    TableName       "testImFileNative_dir"
    Exec            to_json();
</Output>
Input sample

The following is a log record sample read by NXLog.

{
  "AccessTime": "2021-03-24T16:30:43.000000+01:00",
  "URL": "https://nxlog.co",
  "Title": "High Performance Log Collection Solutions",
  "Username": "user1"
}
Output sample

The following is the JSON-formatted log record that will be sent to the Microsoft Azure Sentinel server.

{
  "EventReceivedTime": "2021-03-24T17:14:23.908155+01:00",
  "SourceModuleName": "file",
  "SourceModuleType": "im_file",
  "AccessTime": "2021-03-24T16:30:43.000000+01:00",
  "URL": "https://nxlog.co",
  "Title": "High Performance Log Collection Solutions",
  "Username": "user1",
  "EventType": "browser-history"
}