fix(crowdsec): update whitelist.yaml to prevent false positive

false positive:
- nextcloud thumbnail/preview 404 problem (crowdsecurity/http-probing)

config/node/fw/nftables.conf.j2

@@ -82,6 +82,8 @@ table inet filter {
         chain global {
                 # invalid packets
                 ct state invalid drop comment "deny invalid connection"
+                # VPN connection exception handling
+                udp dport $PORTS_VPN return comment "return vpn connection to input and forward chain"
                 # crowdsec
                 ip saddr @crowdsec-blacklists counter drop comment "deny all crowdsec blacklist"
                 ip6 saddr @crowdsec6-blacklists counter drop comment "deny all ipv6 crowdsec blacklist"

config/services/systemd/common/crowdsec/bouncers/whitelists.yaml.j2

@@ -18,4 +18,6 @@ whitelist:
         - "evt.Meta.target_fqdn == '{{ services['immich']['domain']['public'] }}.{{ domain['public'] }}' && evt.Meta.http_path contains '/api/assets/' && evt.Meta.http_path contains '/thumbnail'"
         # opencloud chunk request false positive
         - "evt.Meta.target_fqdn == '{{ services['opencloud']['domain']['public'] }}.{{ domain['public'] }}' && evt.Meta.http_path contains '/js/chunks/'"
+        # nextcloud thumbnail/preview request error false positive
+        - "evt.Meta.target_fqdn == '{{ services['nextcloud']['domain']['public'] }}.{{ domain['public'] }}' && evt.Meta.http_status == '404' && evt.Meta.http_verb == 'GET' &&  evt.Meta.http_path startsWith '/index.php/core/preview?'"
 {% endif %}

docs/issues/crowdsec/260502_nextcloud.md

@@ -21,9 +21,13 @@
 - 2026-05-02: Find the false positive case, and add whitelist
 - 2026-05-03: Install crowdsecurity/nextcloud-whitelist parser
 - 2026-05-03: Make previous expressions annotation
+- 2026-05-07: Find the false positive case, which is not on `crowdsecurity/nextcloud-whitelist`
+- 2026-05-07: Set whitelist expression
 
 ## Solution
 - Install crowdsecurity/nextcloud-whitelist on auth node
+- Add expression on whitelist
+  - evt.Meta.target_fqdn == '{{ services['nextcloud']['domain']['public'] }}.{{ domain['public'] }}' && evt.Meta.http_status == '404' && evt.Meta.http_verb == 'GET' &&  evt.Meta.http_path startsWith '/index.php/core/preview?'
 
 ### Deprecated solution
 - Access to fw