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Security Violation - Port Scan by NextDNS

Hello NextDNS,

I just noticed, that my firewall blocked the traffic to your DNS server, as one of your servers tried to port scan my network. The ban was performed by CrowdSec.

Looks like, I'm not the only one noticed being scanned by this IP:

https://app.crowdsec.net/cti/45.90.30.0

 

May you explain, why you are performing such scans on your users?

 

Here the output of the cscli, if needed

root@OPNsense:~ # cscli decisions list -m -a -t ban --origin crowdsec | grep 45.90.30.0
| 48771938 | crowdsec | Ip:45.90.30.0      | firewallservices/pf-scan-multi_ports | ban    | US      | 34939 nextdns, Inc.                   | 19     | 15m40s     | 34963    | localhost |
root@OPNsense:~ # 34963
root@OPNsense:~ # cscli alerts inspect 34963

################################################################################################

 - ID           : 34963
 - Date         : 2025-09-11T13:13:33Z
 - Machine      : localhost
 - Simulation   : false
 - Remediation  : true
 - Reason       : firewallservices/pf-scan-multi_ports
 - Events Count : 19
 - Scope:Value  : Ip:45.90.30.0
 - Country      : US
 - AS           : nextdns, Inc.
 - Begin        : 2025-09-11 13:01:00.535888474 +0000 UTC
 - End          : 2025-09-11 13:02:36.670421869 +0000 UTC
 - UUID         : beb62fad-36c0-4054-8d88-23590cc87209

╭───────────────────────────────────────────────────────────────────────╮
│ Active Decisions                                                      │
├──────────┬───────────────┬────────┬────────────┬──────────────────────┤
│    ID    │  scope:value  │ action │ expiration │      created_at      │
├──────────┼───────────────┼────────┼────────────┼──────────────────────┤
│ 48771938 │ Ip:45.90.30.0 │ ban    │ 15m19s     │ 2025-09-11T13:13:33Z │
╰──────────┴───────────────┴────────┴────────────┴──────────────────────╯

 - Context  :
╭──────────┬───────────╮
│    Key   │   Value   │
├──────────┼───────────┤
│ dst_port │ tcp:21070 │
│ dst_port │ tcp:51529 │
│ dst_port │ tcp:24948 │
│ dst_port │ tcp:43535 │
│ dst_port │ tcp:3699  │
│ dst_port │ tcp:64590 │
│ dst_port │ tcp:6345  │
│ dst_port │ tcp:6002  │
│ dst_port │ tcp:33976 │
│ dst_port │ tcp:8364  │
│ dst_port │ tcp:2928  │
│ dst_port │ tcp:59117 │
│ dst_port │ tcp:52315 │
│ dst_port │ tcp:51710 │
│ dst_port │ tcp:11476 │
│ dst_port │ tcp:40199 │
╰──────────┴───────────╯

3 replies

null
    • NextDNs
    • 3 days ago
    • Reported - view

    Is the source port 53 by any chance?

      • Kevin.47
      • 2 days ago
      • Reported - view

       If I watch the traffic from NextDNS I can see traffic from 853 being blocked:

      Not sure why... As this it he DNS over TLS Port right? Outbound is allowed.

      This is happening for all DNS servers. 

      • NextDNs
      • yesterday
      • Reported - view

       this is the return traffic from DoT. It’s likely a misconfiguration of this tool.

Content aside

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