ModSecurity breaking the Wordpress Theme editor, cannot write proper exclusion rules-CodePudding

This is about writing proper ModSecurity rules. I hope there is an expert out there who can help me.

I have ModSecurity 2.9.3 and the OWASP CRS 3.3.2 security rules running on my new VPS (Virtualmin).

I enabled the REQUEST-903.9002-WORDPRESS-EXCLUSION-RULES, and it mostly seem to work.

The Wordpress theme editor, however, does not. When saving, it gets a 403 response ("Saving failed").

I know it's Modsecurity because when I disable it everything works fine.

I investigated the audit log and have created corresponding rules in REQUEST-900-EXCLUSION-RULES-BEFORE-CRS.conf:

SecRule REQUEST_URI "@contains /wp-json/wp/v2/template-parts/" \
"id:10000002,\
phase:2,\
pass,\
nolog,\
ctl:ruleRemoveTargetById=949110;ARGS=content,\
ctl:ruleRemoveTargetById=941100;ARGS=content,\
ctl:ruleRemoveTargetById=941160;ARGS=content,\
ctl:ruleRemoveTargetById=941180;ARGS=content,\
ctl:ruleRemoveTargetById=932105;ARGS=content,\
ctl:ruleRemoveTargetById=980130;ARGS=content"

SecRule REQUEST_URI "@contains /wp-json/wp/v2/templates/<hostname>/page/" \
"id:10000003,\
phase:2,\
pass,\
nolog,\
ctl:ruleRemoveTargetById=949110;ARGS=content,\
ctl:ruleRemoveTargetById=941100;ARGS=content,\
ctl:ruleRemoveTargetById=941160;ARGS=content,\
ctl:ruleRemoveTargetById=941180;ARGS=content,\
ctl:ruleRemoveTargetById=932105;ARGS=content,\
ctl:ruleRemoveTargetById=980130"

I know the rules are being read, because when I mess with the request uri I can get Wordpress to stop working altogether.

However, the problem persist. I am not a Modsecurity expert; I understand my exclusion rules are not properly written, but I cannot get them to work.

Here's a few samples of the false positives from the Audit log, triggered by the Wordpress theme editor:

--48163009-H--
Message: Warning. Pattern match "(?:;|\\{|\\||\\|\\||&|&&|\\n|\\r|\\$\\(|\\$\\(\\(|`|\\${|<\\(|>\\(|\\(\\s*\\))\\s*(?:{|\\s*\\(\\s*|\\w =(?:[^\\s]*|\\$.*|\\$.*|<.*|>.*|\\'.*\\'|\".*\")\\s |!\\s*|\\$)*\\s*(?:'|\")*(?:[\\?\\*\\[\\]\\(\\)\\-\\| \\w'\"\\./\\\\] /)?[\\\\'\"]*(?:s[\\\\'\"]* ..." at ARGS:content. [file "/etc/modsecurity/rules/REQUEST-932-APPLICATION-ATTACK-RCE.conf"] [line "158"] [id "932105"] [msg "Remote Command Execution: Unix Command Injection"] [data "Matched Data: {\x22top found within ARGS:content: <!-- wp:template-part {\x22slug\x22:\x22header\x22,\x22theme\x22:\x22<hostname>\x22,\x22tagName\x22:\x22header\x22} /-->\x0a\x0a<!-- wp:group {\x22tagName\x22:\x22main\x22,\x22style\x22:{\x22spacing\x22:{\x22padding\x22:{\x22top\x22:\x220\x22,\x22right\x22:\x220\x22,\x22bottom\x22:\x220\x22,\x22left\x22:\x220\x22},\x22blockGap\x22:\x220\x22}}} -->\x0a<main class=\x22wp-block-group\x22 style=\x22padding-top:0;padding-right:0;padding-bottom:0;padding-left:0\x2..."] [severity "CRITICAL"] [ver "OWASP_CRS/3.3.2"]



Message: Warning. detected XSS using libinjection. [file "/etc/modsecurity/rules/REQUEST-941-APPLICATION-ATTACK-XSS.conf"] [line "55"] [id "941100"] [msg "XSS Attack Detected via libinjection"] [data "Matched Data: XSS data found within ARGS:content: <!-- wp:template-part {\x22slug\x22:\x22header\x22,\x22theme\x22:\x22<hostname>\x22,\x22tagName\x22:\x22header\x22} /-->\x0a\x0a<!-- wp:group {\x22tagName\x22:\x22main\x22,\x22style\x22:{\x22spacing\x22:{\x22padding\x22:{\x22top\x22:\x220\x22,\x22right\x22:\x220\x22,\x22bottom\x22:\x220\x22,\x22left\x22:\x220\x22},\x22blockGap\x22:\x220\x22}}} -->\x0a<main class=\x22wp-block-group\x22 style=\x22padding-top:0;padding-right:0;padding-bottom:0;padding-left:0\x2..."] [severity "CRITICAL"] [ver "OWASP_CRS/3.3.2"] [tag "application-multi"] [tag "language-multi"] [tag "platform-multi"] [tag "attack-xss"] [tag "paranoia-level/1"] [tag "OWASP_CRS"] [tag "capec/1000/152/242"]

Apache-Error: [file "apache2_util.c"] [line 273] [level 3] ModSecurity: Warning. Matched phrase "<!--" at ARGS:content. [file "/etc/modsecurity/rules/REQUEST-941-APPLICATION-ATTACK-XSS.conf"] [line "250"] [id "941180"] [msg "Node-Validator Blacklist Keywords"] [data "Matched Data: <!-- found within ARGS:content: <!-- wp:template-part {\\\\x22slug\\\\x22:\\\\x22header\\\\x22,\\\\x22theme\\\\x22:\\\\x22<hostname>\\\\x22,\\\\x22tagname\\\\x22:\\\\x22header\\\\x22} /-->\\\\x0a\\\\x0a<!-- wp:group {\\\\x22tagname\\\\x22:\\\\x22main\\\\x22,\\\\x22style\\\\x22:{\\\\x22spacing\\\\x22:{\\\\x22padding\\\\x22:{\\\\x22top\\\\x22:\\\\x220\\\\x22,\\\\x22right\\\\x22:\\\\x220\\\\x22,\\\\x22bottom\\\\x22:\\\\x220\\\\x22,\\\\x22left\\\\x22:\\\\x220\\\\x22},\\\\x22blockgap\\\\x22:\\\\x220\\\\x22}}} -->\\\\x0a<main class=\\\\x22wp-block-group\\\\x22 style=\\\\x22padding-top:0;padding-right:0;padding-bottom:0;padding-left:0\\\\x22><!..."] [severity "CRITICAL"] [ver "OWASP_CRS/3.3.2"] [tag "application-multi"] [tag "language-multi"] [tag "platform-multi"] [tag "attack-xss"] [tag "paranoia-level/1"] [tag "OWASP_CRS"] [tag "capec/1000/152/242"] [hostname "sit.<hostname>.com"] [uri "/wp-json/wp/v2/templates/<hostname>/page"] [unique_id "Y7-6B6WOVEBhE0cscXvdvgAAERU"]
Apache-Error: [file "apache2_util.c"] [line 273] [level 3] [client 92.46.0.178] ModSecurity: Access denied with code 403 (phase 2). Operator GE matched 5 at TX:anomaly_score. [file "/etc/modsecurity/rules/REQUEST-949-BLOCKING-EVALUATION.conf"] [line "93"] [id "949110"] [msg "Inbound Anomaly Score Exceeded (Total Score: 20)"] [severity "CRITICAL"] [ver "OWASP_CRS/3.3.2"] [tag "application-multi"] [tag "language-multi"] [tag "platform-multi"] [tag "attack-generic"] [hostname "<hostname>.com"] [uri "/wp-json/wp/v2/templates/<hostname>/page"] [unique_id "Y7-6B6WOVEBhE0cscXvdvgAAERU"]

================================================

[EDIT] For anybody interested, this was SOLVED by changing the rule as such:

SecRule REQUEST_URI "@beginsWith /wp-json/wp/v2/template" \
"id:10000002,\
phase:2,\
pass,\
nolog,\
ctl:ruleRemoveTargetById=949110;ARGS:content,\
ctl:ruleRemoveTargetById=941100;ARGS:content,\
ctl:ruleRemoveTargetById=941160;ARGS:content,\
ctl:ruleRemoveTargetById=941180;ARGS:content,\
ctl:ruleRemoveTargetById=932105;ARGS:content,\
ctl:ruleRemoveTargetById=980130;ARGS:content"

I merged the two block of rules into one, and changed = to : as suggested by azurit. Thanks!

CodePudding user response：

Never exclude rules 949XXX and 980XXX as it's the same as completely disabling CRS.

Your rules are more or less correct except this syntax problem:

ARGS=content

It should be:

ARGS:content