Open redirect: obunsha.co.jp

 1name: "Open redirect: obunsha.co.jp"
 2description: |
 3  Detects messages containing Obunsha's passnavi redirect service that can be exploited
 4  to redirect users to malicious sites. This has been used in phishing campaigns.  
 5type: "rule"
 6severity: "medium"
 7source: |
 8  type.inbound
 9  and any(body.links,
10          // Look for Obunsha passnavi URLs
11          .href_url.domain.domain == "passnavi.obunsha.co.jp"
12          and strings.icontains(.href_url.path, '/ct.html')
13          and strings.icontains(.href_url.query_params, 'uri=')
14          // Make sure it's not redirecting back to obunsha domains
15          and not regex.icontains(.href_url.query_params,
16                                  'uri=(?:https?(?:%3a|:))?(?:%2f|\/){2}[^&]*obunsha\.co\.jp(?:\&|\/|$|%2f)'
17          )
18  )
19  // Exclude legitimate Obunsha domains as senders
20  and not sender.email.domain.root_domain == "obunsha.co.jp"
21  
22  // negate highly trusted sender domains unless they fail DMARC authentication
23  and not (
24    sender.email.domain.root_domain in $high_trust_sender_root_domains
25    and coalesce(headers.auth_summary.dmarc.pass, false)
26  )  
27attack_types:
28  - "Credential Phishing"
29  - "Malware/Ransomware"
30tactics_and_techniques:
31  - "Open redirect"
32detection_methods:
33  - "Sender analysis"
34  - "URL analysis"
35id: "e972dacf-0316-57d0-b135-38517042b9e8"