Performance issues with ModSecurity2/Alpine/PCRE2

まず、提供された Docker コマンドと shell 負荷スクリプトを使用して、OWASP ModSecurity CRS の Debian イメージと Alpine イメージで報告された比較を再現します。CPU 使用率とリクエストの所要時間を比較し、その後、PCRE2 が関係する ModSecurity 2.9.10 の Apache パスを追跡します。原因を特定し、同等のパフォーマンスを実証するか、確認済みの制限を文書化できれば完了です。

Describe the bug

When using PCRE2 instead of PCRE1 there is a significant performance loss with ModSecurityV2 on Alpine Linux compared to Debian.
A ModSec2 installation with Apache on Alpine Linux handles requests much slower and is using up considerable amounts of CPU ressources.
This behavior can be reproduced using the official OWASP CRS container image: https://github.com/coreruleset/modsecurity-crs-docker
The test described below results in about 5% to 10% higher CPU usage on the alpine image compared to the debian image.
In this screenshot from btop you can see the difference in the CPU usage for the same workfload(left debian, right alpine):

This difference seems to be dependent on the exact usecase. In one of our production setups we had about 10 times higher CPU loads under certain conditions. This even lets the OpenShift healthchecks fail for these containers due to timeouts.
I focus on the simple request in this issue, because our productive setup is much more complicated to reproduce.

@airween is already aware of this issue, but was unable to reproduce it until now.

Logs and dumps

No problems discoverable in the logs

To Reproduce

The issue can be reproduced with the official OWASP-ModSecurity Docker image. I used the following Docker run commands to start the container with either the most current debian or Alpine image.

Debian: owasp/modsecurity-crs:apache
Alpine: owasp/modsecurity-crs:apache-alpine

Docker run command:

docker run \
   -ti \
   -p 9090:8080 \
   --rm \
   -v /tmp/host-fs-auditlog.log:/var/log/modsec_audit.log \
   -v /tmp/host-fs-errorlog.log:/var/log/modsec_error.log \
   -e MODSEC_AUDIT_ENGINE=on \
   -e LOGLEVEL=warn \
   -e ERRORLOG=/var/log/modsec_error.log \
   -e BLOCKING_PARANOIA=2 \
   -e DETECTION_PARANOIA=2 \
   -e ENFORCE_BODYPROC_URLENCODED=1 \
   -e ANOMALY_INBOUND=10 \
   -e ANOMALY_OUTBOUND=5 \
   -e ALLOWED_METHODS="GET HEAD POST OPTIONS PUT PATCH DELETE" \
   -e ALLOWED_REQUEST_CONTENT_TYPE="application/x-www-form-urlencoded|multipart/form-data|multipart/related|text/xml|application/xml|application/soap+xml|application/json|application/cloudevents+json|application/cloudevents-batch+json|text/plain" \
   -e ALLOWED_REQUEST_CONTENT_TYPE_CHARSET="utf-8|iso-8859-1" \
   -e ALLOWED_HTTP_VERSIONS="HTTP/1.1 HTTP/2 HTTP/2.0" \
   -e RESTRICTED_EXTENSIONS=".cmd/ .com/ .config/ .dll/" \
   -e RESTRICTED_HEADERS="/proxy/ /if/" \
   -e STATIC_EXTENSIONS="/.jpg/ /.jpeg/ /.png/ /.gif/" \
   -e MAX_NUM_ARGS=128 \
   -e ARG_NAME_LENGTH=50 \
   -e ARG_LENGTH=200 \
   -e TOTAL_ARG_LENGTH=6400 \
   -e MAX_FILE_SIZE=100000 \
   -e COMBINED_FILE_SIZES=1000000 \
   -e TIMEOUT=60 \
   -e SERVER_ADMIN=root@localhost \
   -e SERVER_NAME=localhost \
   -e PORT=8080 \
   -e MODSEC_RULE_ENGINE=on \
   -e MODSEC_REQ_BODY_ACCESS=on \
   -e MODSEC_REQ_BODY_LIMIT=13107200 \
   -e MODSEC_REQ_BODY_NOFILES_LIMIT=131072 \
   -e MODSEC_RESP_BODY_ACCESS=off \
   -e MODSEC_RESP_BODY_LIMIT=524288 \
   -e MODSEC_PCRE_MATCH_LIMIT=1000 \
   -e MODSEC_PCRE_MATCH_LIMIT_RECURSION=1000 \
   -e VALIDATE_UTF8_ENCODING=1 \
   -e CRS_ENABLE_TEST_MARKER=1 \
   -e PROXY_SSL_VERIFY=off \
   -e PROXY_SSL=on \
   -e BACKEND="https://httpbin.org/" \
   owasp/modsecurity-crs:apache-alpine

I generated the load with a small shell script, that performs about 20 curl requests with some cookies per second:

#!/bin/bash

while [ true ] 
do

sleep 0.05

curl -s -k "http://<ip or url of running waf>:9090/status/200" -H "Cookie: NG_TRANSLATE_LANG_KEY=en; _n2os-webconsole_session-33564f983wewretgdfghdjfg5e14bf3f70901b9430f3b=b0d87ec87b9dfgdfgwerertw08cb0c89; XSRF-TOKEN-2dsfds86c-1be4-473b-b10f-6f7sdfwe589b2=_of55PO8gv3YZLNijkqp9bAMi_yEEVbIBXbHDE1x274Mlp_J72-FnWiocfPZVgR2bTwpAsd6XmOXHmMAldogoQ; atuserid=%7B%22name%22%3A%22atuserid%22%2C%22val%22%3A%werw-4a51-4ac4-a80e-c142ewrwerw%22options%22%3A%7B%22end%22%3A%werwe-07-15T05%3A56%3A01.951Z%22%2C%22path%22%3A%22%2F%22%7D%7D; atidvisitor=%7B%22name%22%3A%22atidvisitor%22%2C%22val%22%3A%7B%22vrn%22%3A%22-werwerwe234324-%22%7D%2C%22options%22%3A%7B%22path%22%3A%22%2F%22%2C%22session%22%23423423%2C%22end%22%23423423%7D%7D; 3db4ccd6a2c6234234234423_n2os-webconsole_session-ewrewr2342356235werwerwer23451234=856020593f6a7d6a62b9ba4ef6afea7c; XSRF-TOKEN-f66e8519-be08-4679-8995-9623423423wec27171=DdCIiYRrsDD1A53RHeVSRoFCc5FMHfeuaAleBP7_40Zpcy0wDDFzTd__UsMQ3MT234234ZeSN-5QAPLCumOUiyw" -w "%{time_total}\n" -o /dev/null >> ./$1

done

Expected behavior

The expected behavior would be a similar performance of the debain and alpine images.

Server (please complete the following information):

• ModSecurity version 2.9.10
• WebServer: apache-2.4.63
• Debian and Alpine container images
• Rocky Linux 9.6 docker-ce host system

Rule Set (please complete the following information):

• CRS 4.15.0

Additional context

If further information is needed, please feel free to ask