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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.)

Kevin Weil
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9 Answers9

42

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.

Arjan
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Spider
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  • mod_dumpio doesn't sound like it can be restricted to a specific location context, it's only server-wide – Josip Rodin Jan 31 '19 at 11:26
  • @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_ – Marki555 Oct 20 '20 at 21:07
25

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
Jeroen Vermeulen - MageHost
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    modsecurity has Ubuntu packages whereas others do not. – Raul Nohea Goodness Oct 19 '17 at 15:54
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    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. – Elnur Abdurrakhimov May 28 '18 at 18:15
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    For `http 2.4` yum package is `mod24_security` and config file location is `/etc/httpd/conf.d/mod_security.conf` – HeatfanJohn Feb 10 '19 at 22:47
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    dumpio looks like it's limited to the first 256 bytes of the body, then truncates the rest. – Dave Brunkow Sep 02 '21 at 15:53
  • 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? – Alex Feb 16 '22 at 12:54
  • This example logs all traffic quite extended. At https://github.com/SpiderLabs/ModSecurity/wiki/Reference-Manual-%28v2.x%29#SecAuditLog it says "Scope Any" so it should be possible to use this directive within or – Jeroen Vermeulen - MageHost Feb 16 '22 at 13:39
16

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"}
Josip Rodin
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hg8
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    The default config logged nothing for me. I had to set SecRuleEngine On SecAuditEngine On – ropo Feb 23 '23 at 09:29
13

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

w00d
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    cool! it makes absolutly sense to dump post data for logfile analysis i.e. for things like sql injection attempts. – KIC Sep 09 '14 at 12:48
2

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

hpr
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2

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.

Assaf Lavie
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    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. – Kevin Weil Jun 13 '09 at 04:33
  • Any good framework should have pre and post filters, or the equivalent of middleware which will allow you to fire and forget. – blockhead Oct 15 '12 at 07:57
0

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).

MediaVince
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siliconrockstar
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0

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

bimosaurus
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    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 – Al Longley Apr 10 '22 at 03:29
-2

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

Daniel
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