Best way to log POST data in Apache?

Question

Imagine you have a site API that accepts data in the form of GET requests with parameters, or as POST requests (say, with standard url-encoded, &-separated POST data). If you want to log and analyze API calls, the GET requests will be easy, because they will be in the apache log. Is there a simple way to get the POST data in the apache log as well?

(Of course we could log the POST data explicitly in the application, but I'd like to have an configuration-level way that let me not worry about it in code.)

Genevieve

Related question at ServerFault: serverfault.com/questions/51295/logging-http-post-in-apache – Incarnation

Answer 1

Use Apache's mod_dumpio. Be careful for obvious reasons.

Note that mod_dumpio stops logging binary payloads at the first null character. For example a multipart/form-data upload of a gzip'd file will probably only show the first few bytes with mod_dumpio.

Also note that Apache might not mention this module in httpd.conf even when it's present in the /modules folder. Just manually adding LoadModule will work fine.

Thailand

mod_dumpio doesn't sound like it can be restricted to a specific location context, it's only server-wide – Rebeckarebeka

@JosipRodin should be possible via LogLevel (that can be set also in vhost or dir context). Additionally, mod_dumpio needs to be configured to LogLevel trace7 – Stylograph

Answer 2

You can install mod_security and put in /etc/modsecurity/modsecurity.conf:

SecRuleEngine On
SecAuditEngine On
SecAuditLog /var/log/apache2/modsec_audit.log
SecRequestBodyAccess on
SecAuditLogParts ABIJDFHZ

Arson

modsecurity has Ubuntu packages whereas others do not. – Madagascar

What others? Like dumpio? It's already included with Apache HTTPD — at least in Ubuntu 16.04. That's why there's no separate package for it. You just need to enable it. – Pressurecook

For http 2.4 yum package is mod24_security and config file location is /etc/httpd/conf.d/mod_security.conf – Westward

dumpio looks like it's limited to the first 256 bytes of the body, then truncates the rest. – Thwart

Does this log all requests or only such with security violations? Can it be limited to certain URLs, for example if I want to debug only one specific form? – Torus

This example logs all traffic quite extended. At github.com/SpiderLabs/ModSecurity/wiki/… it says "Scope Any" so it should be possible to use this directive within <Location> or <Directory> – Arson

Answer 3

You can use [ModSecurity][1] to view POST data.

Install on Debian/Ubuntu:

$ sudo apt install libapache2-mod-security2

Use the recommended configuration file:

$ sudo mv /etc/modsecurity/modsecurity.conf-recommended /etc/modsecurity/modsecurity.conf

Reload Apache:

$ sudo service apache2 reload

---

You will now find your data logged under /var/log/apache2/modsec_audit.log

$ tail -f /var/log/apache2/modsec_audit.log
--2222229-A--
[23/Nov/2017:11:36:35 +0000] 
--2222229-B--
POST / HTTP/1.1
Content-Type: application/json
User-Agent: curl
Host: example.com

--2222229-C--
{"test":"modsecurity"}

Unconscious

The default config logged nothing for me. I had to set SecRuleEngine On SecAuditEngine On – Gisele

Answer 4

Though It's late to answer. This module can do: https://github.com/danghvu/mod_dumpost

Icily

cool! it makes absolutly sense to dump post data for logfile analysis i.e. for things like sql injection attempts. – Judgment

Answer 5

I would do it in the application, actually. It's still configurable at runtime, depending on your logger system, of course. For example, if you use Apache Log (log4j/cxx) you could configure a dedicated logger for such URLs and then configure it at runtime from an XML file.

Renatorenaud

My concern there is that EVERY api handler will have to log the data at the beginning -- easy to forget as you're adding, and at best it's just added boilerplate. – Genevieve

Any good framework should have pre and post filters, or the equivalent of middleware which will allow you to fire and forget. – Chirm

Came here after apache log4j vulnerability – Christophe

Answer 6

Enable mod_dumpio

• for Debian-based OS

  sudo a2enmod dump_io

• for RedHat-based OS

  nothing to do, it is enabled by default

Add mod_dumpio to your virtual host configuration

<VirtualHost *:8080>
  ServerName  localhost

  ErrorLog "/var/log/httpd/error.log"
  CustomLog "/var/log/httpd/access.log" combined

  DumpIOInput On
  DumpIOOutput On
  LogLevel dumpio:trace7    
</VirtualHost>

Restart Apache

Agonic

Answer 7

An easier option may be to log the POST data before it gets to the server. For web applications, I use Burp Proxy and set Firefox to use it as an HTTP/S proxy, and then I can watch (and mangle) data 'on the wire' in real time.

For making API requests without a browser, SoapUI is very useful and may show similar info. I would bet that you could probably configure SoapUI to connect through Burp as well (just a guess though).

Expediency

Answer 8

You can also use mod DumpIO, activate it, and load from your Apache Log Conf. Define log name as postdata name, and load to AccessLog statement

#AccessLog /path/to/your/log/abc.access.log combine

AccessLog /path/to/your/log/abc.access.log postdata

Shoulder

This does not work. AccessLog is not an Apache config directive, "postdata" is not defined anywhere, DumpIO always seems to default to "/var/log/apache2/error.log" even if you specify ErrorLog to point elsewhere – Shaggy

Answer 9

You can also use the built-in forensic log feature.

Crossjack

I don't see any to ask mod_log_forensic to log POST data. Am I missing something? – Fortyfive

httpd.apache.org/docs/2.4/mod/mod_log_forensic.html#forensiclog indicates this module can only be as granular as a virtual host – Rebeckarebeka

forensic log doesn't log content – Longlegged