Nginx+libmodsecurity and work with gzip

[RunFox]

Hello. I use Nginx 1.20.1 + libmodsecurity-3.0.4-4.el8 as reverse proxy. When we receive request with Content-Encoding: gzip and Content-Type: application/json - activate rule from default modsecurity.conf:

SecRule REQBODY_ERROR "!@eq 0" \
"id:'200002', phase:2,t:none,log,deny,status:400,msg:'Failed to parse request body.',logdata:'%{reqbody_error_msg}',severity:2"

As I understand - we recieve data with gzip as binary content, then it send to modsecurity in binary fromat and json parser give error because data is not valid json. I think, this is actually true for xml and any another data with compression.Is there way to work with compressed data with Modsecurity or workaround? I understand, that i can disable rule for analyze json and xml - but it's bad way, thats affect level of security.

[airween]

May be you should take a look at this:

https://github.com/coreruleset/body-decompress-plugin

Perhaps you will get some ideas.

[RunFox]

Hi, @airween Do you work with this plugin? Does it work with modsecurity v3? I see this plugin for response body. Is your idea try for rewrite for processing gzip request body in fly?

[airween]

Do you work with this plugin?

no, just tested,

Does it work with modsecurity v3?

this plugin has made for mod_security2, but with few modifications it works with v3 too.

I see this plugin for response body. Is your idea try for rewrite for processing gzip request body in fly?

No, the author is @azurit.

[RunFox]

Thank you for idea)

this plugin has made for mod_security2, but with few modifications it works with v3 too

What kind of modification was done? In plugin's description there is information "for embedded". Did you try it with reverse-proxy configuration? How fast does it work?)

[azurit]

As you are running in reverse proxy mode, please see SecDisableBackendCompression ModSecurity configuration directive.

[RunFox]

As you are running in reverse proxy mode, please see SecDisableBackendCompression ModSecurity configuration directive.

@azurit hello and thank you for anwer) Unfortunately, as i know, SecDisableBackendCompression is not support in modsecurity v3

[azurit]

Ok, so please try my plugin as @airween suggested, as far as i remember, it should work with modsec3. Note that you need support for Lua in modsec.

[RunFox]

@azurit thank you, i will try)