owasp-modsecurity / owasp-modsecurity/ModSecurity-nginx

Nginx+libmodsecurity and work with gzip

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Description

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.

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Research direction

Start with the Nginx reverse-proxy setup and the SecRule for REQBODY_ERROR in the default modsecurity.conf, reproducing the request with Content-Encoding: gzip and application/json. Trace how compressed request bodies reach libmodsecurity and define done as a confirmed supported behavior or documented workaround that preserves request-body inspection for JSON and XML.

Written by the indexing model from the issue text.

Assessment

Tech stack
nginx
Domain
security
Issue type
Bug
Difficulty
5/5
Estimated time
Over a week
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
20/100

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