Callback phishing via Adobe Sign comment
This rule inspects messages originating from legitimate Adobe Sign infrastructure, with content matching Callback Phishing criteria, in the body, requiring at least one brand name, as well as 3 matching Callback Phishing terms and a phone number.
Sublime rule (View on GitHub)
1name: "Callback phishing via Adobe Sign comment"
2description: |
3 This rule inspects messages originating from legitimate Adobe Sign infrastructure, with content matching Callback Phishing criteria, in the body, requiring at least one brand name, as well as 3 matching Callback Phishing terms and a phone number.
4type: "rule"
5severity: "high"
6source: |
7 type.inbound
8 and length(attachments) == 0
9
10 // Legitimate Docusign sending infratructure
11 and sender.email.domain.root_domain == 'adobesign.com'
12 and (headers.auth_summary.spf.pass or headers.auth_summary.dmarc.pass)
13 and (
14 // this section is synced with attachment_callback_phish_with_pdf.yml and attachment_callback_phish_with_img.yml
15 regex.icontains(strings.replace_confusables(body.current_thread.text),
16 '(p.{0,3}a.{0,3}y.{0,3}p.{0,3}a.{0,3}l|ma?c.?fee|n[o0]rt[o0]n|geek.{0,5}squad|ebay|symantec|best buy|lifel[o0]c|secure anywhere|starz|utilities premium|pc security|at&t)'
17 )
18 or any(ml.logo_detect(file.message_screenshot()).brands,
19 .name in ("PayPal", "Norton", "GeekSquad", "Ebay", "McAfee", "AT&T")
20 )
21 )
22 and (
23 (
24 // this seciton is synced with attachment_callback_phish_with_img.yml and attachment_callback_phish_with_pdf.yml
25 // however, the 3 of logic and requiring a phone number is specific to this rule in order to reduce FPs
26 // caused by messages which mention cancelling or otherwise managing a subscription
27 // it is also synced and below for message_screenshot OCR output
28 3 of (
29 strings.icontains(body.current_thread.text, 'purchase'),
30 strings.icontains(body.current_thread.text, 'payment'),
31 strings.icontains(body.current_thread.text, 'transaction'),
32 strings.icontains(body.current_thread.text, 'subscription'),
33 strings.icontains(body.current_thread.text, 'antivirus'),
34 strings.icontains(body.current_thread.text, 'order'),
35 strings.icontains(body.current_thread.text, 'support'),
36 strings.icontains(body.current_thread.text, 'help line'),
37 strings.icontains(body.current_thread.text, 'receipt'),
38 strings.icontains(body.current_thread.text, 'invoice'),
39 strings.icontains(body.current_thread.text, 'call'),
40 strings.icontains(body.current_thread.text, 'cancel'),
41 strings.icontains(body.current_thread.text, 'renew'),
42 strings.icontains(body.current_thread.text, 'refund'),
43 regex.icontains(body.current_thread.text, "(?:reach|contact) us at"),
44 strings.icontains(body.current_thread.text, "+1"),
45 strings.icontains(body.current_thread.text, "amount"),
46 strings.icontains(body.current_thread.text, "charged"),
47 strings.icontains(body.current_thread.text, "crypto"),
48 strings.icontains(body.current_thread.text, "wallet address"),
49 regex.icontains(body.current_thread.text, '\$\d{3}\.\d{2}\b'),
50 )
51 // phone number regex
52 and regex.icontains(body.current_thread.text,
53 '\+?([ilo0-9]{1}.)?\(?[ilo0-9]{3}?\)?.[ilo0-9]{3}.?[ilo0-9]{4}',
54 '\+?([ilo0-9]{1,2})?\s?\(?\d{3}\)?[\s\.\-⋅]{0,5}[ilo0-9]{3}[\s\.\-⋅]{0,5}[ilo0-9]{4}'
55 )
56 )
57 or (
58 // this seciton is synced with attachment_callback_phish_with_img.yml and attachment_callback_phish_with_pdf.yml
59 // and above for current_thread.text
60 //
61 // This rule makes use of a beta feature and is subject to change without notice
62 // using the beta feature in custom rules is not suggested until it has been formally released
63 //
64 3 of (
65 strings.icontains(beta.ocr(file.message_screenshot()).text, 'purchase'),
66 strings.icontains(beta.ocr(file.message_screenshot()).text, 'payment'),
67 strings.icontains(beta.ocr(file.message_screenshot()).text, 'transaction'),
68 strings.icontains(beta.ocr(file.message_screenshot()).text,
69 'subscription'
70 ),
71 strings.icontains(beta.ocr(file.message_screenshot()).text, 'antivirus'),
72 strings.icontains(beta.ocr(file.message_screenshot()).text, 'order'),
73 strings.icontains(beta.ocr(file.message_screenshot()).text, 'support'),
74 strings.icontains(beta.ocr(file.message_screenshot()).text, 'help line'),
75 strings.icontains(beta.ocr(file.message_screenshot()).text, 'receipt'),
76 strings.icontains(beta.ocr(file.message_screenshot()).text, 'invoice'),
77 strings.icontains(beta.ocr(file.message_screenshot()).text, 'call'),
78 strings.icontains(beta.ocr(file.message_screenshot()).text, 'helpdesk'),
79 strings.icontains(beta.ocr(file.message_screenshot()).text, 'cancel'),
80 strings.icontains(beta.ocr(file.message_screenshot()).text, 'renew'),
81 strings.icontains(beta.ocr(file.message_screenshot()).text, 'refund'),
82 regex.icontains(beta.ocr(file.message_screenshot()).text,
83 "(?:reach|contact) us at"
84 ),
85 strings.icontains(beta.ocr(file.message_screenshot()).text, '+1'),
86 strings.icontains(beta.ocr(file.message_screenshot()).text, 'amount'),
87 strings.icontains(beta.ocr(file.message_screenshot()).text, 'charged'),
88 strings.icontains(beta.ocr(file.message_screenshot()).text, 'crypto'),
89 strings.icontains(beta.ocr(file.message_screenshot()).text,
90 'wallet address'
91 ),
92 regex.icontains(beta.ocr(file.message_screenshot()).text,
93 '\$\d{3}\.\d{2}\b'
94 ),
95 )
96 // phone number regex
97 and regex.icontains(beta.ocr(file.message_screenshot()).text,
98 '\+?([ilo0-9]{1}.)?\(?[ilo0-9]{3}?\)?.[ilo0-9]{3}.?[ilo0-9]{4}',
99 '\+?([ilo0-9]{1,2})?\s?\(?\d{3}\)?[\s\.\-⋅]{0,5}[ilo0-9]{3}[\s\.\-⋅]{0,5}[ilo0-9]{4}'
100 )
101
102 // negate messages with previous threads. While callback phishing with thread hijacking or with current_thread
103 // padded with whitespace and previous threads in the message has been observed, the intetion of using OCR is for image embedded callbacks
104 and not regex.icount(beta.ocr(file.message_screenshot()).text,
105 '(?:from|to|sent|date|cc|subject):'
106 ) > 3
107 // this notation of previous threads often only occurs once
108 and not regex.icontains(beta.ocr(file.message_screenshot()).text,
109 'wrote:[\r\n]'
110 )
111 )
112 )
113attack_types:
114 - "Callback Phishing"
115tactics_and_techniques:
116 - "Evasion"
117 - "Impersonation: Brand"
118 - "Out of band pivot"
119 - "Social engineering"
120detection_methods:
121 - "Content analysis"
122 - "Computer Vision"
123 - "Header analysis"
124 - "Sender analysis"
125 - "URL analysis"
126id: "7eb4516d-f358-5c22-b527-34db0a532df9"