Credential Phishing: Suspicious subject with urgent financial request and link
This rule inspects messages where the subject is suspicious with less than 5 links and a relatively short body. Natural Language Understanding is being used to identify the inclusion of a financial, request, urgency and org entity from an unsolicited sender.
Sublime rule (View on GitHub)
1name: "Credential Phishing: Suspicious subject with urgent financial request and link"
2description: "This rule inspects messages where the subject is suspicious with less than 5 links and a relatively short body. Natural Language Understanding is being used to identify the inclusion of a financial, request, urgency and org entity from an unsolicited sender."
3type: "rule"
4severity: "medium"
5source: |
6 type.inbound
7 and (
8 0 < length(filter(body.links,
9 not strings.ilike(.display_text,
10 "*privacy*",
11 "*terms of service*",
12 "Learn why this is important"
13 )
14 or .display_text is null
15 )
16 ) < 5
17 )
18
19 // negate webinar registrations
20 and not any(body.links,
21 .display_text =~ "REGISTER NOW"
22 and .href_url.domain.root_domain == "secureclick.net"
23 )
24
25 // not all links are unsubscribe links
26 and not all(body.links,
27 (
28 strings.icontains(.display_text, "unsubscribe")
29 and strings.icontains(.href_url.path, "unsubscribe")
30 )
31 or (
32 strings.icontains(.display_text, "deactivate")
33 and strings.icontains(.href_url.path, "DeactivateAccount")
34 )
35 )
36
37 // ignore emails in body
38 and not all(body.links, .href_url.domain.domain in $free_email_providers)
39 and length(body.current_thread.text) < 2000
40 and length(subject.subject) < 100
41
42 // and suspicious subject
43 and regex.icontains(subject.subject,
44 // https://github.com/sublime-security/static-files/blob/master/suspicious_subjects_regex.txt
45 "termination.*notice",
46 "38417",
47 ":completed",
48 "[il1]{2}mit.*ma[il1]{2} ?bo?x",
49 "[il][il][il]egai[ -]",
50 "[li][li][li]ega[li] attempt",
51 "[ng]-?[io]n .*block",
52 "[ng]-?[io]n .*cancel",
53 "[ng]-?[io]n .*deactiv",
54 "[ng]-?[io]n .*disabl",
55 "action.*required",
56 "abandon.*package",
57 "about.your.account",
58 "acc(ou)?n?t (is )?on ho[li]d",
59 "acc(ou)?n?t.*terminat",
60 "acc(oun)?t.*[il1]{2}mitation",
61 "access.*limitation",
62 "account (will be )?block",
63 "account.*de-?activat",
64 "account.*locked",
65 "account.*re-verification",
66 "account.*security",
67 "account.*suspension",
68 "account.has.been",
69 "account.has.expired",
70 "account.will.be.blocked",
71 "account v[il]o[li]at",
72 "activity.*acc(oun)?t",
73 "almost.full",
74 "app[li]e.[il]d",
75 "authenticate.*account",
76 "been.*suspend",
77 "clos.*of.*account.*processed",
78 "confirm.your.account",
79 "courier.*able",
80 "crediential.*notif",
81 "deactivation.*in.*progress",
82 "delivery.*attempt.*failed",
83 "document.received",
84 "documented.*shared.*with.*you",
85 "dropbox.*document",
86 "e-?ma[il1]+ .{010}suspen",
87 "e-?ma[il1]{1} user",
88 "e-?ma[il1]{2} acc",
89 "e-?ma[il1]{2}.*up.?grade",
90 "e.?ma[il1]{2}.*server",
91 "e.?ma[il1]{2}.*suspend",
92 "email.update",
93 "faxed you",
94 "fraud(ulent)?.*charge",
95 "from.helpdesk",
96 "fu[il1]{2}.*ma[il1]+[ -]?box",
97 "has.been.*suspended",
98 "has.been.limited",
99 "have.locked",
100 "he[li]p ?desk upgrade",
101 "heipdesk",
102 "i[il]iega[il]",
103 "ii[il]ega[il]",
104 "incoming e?mail",
105 "incoming.*fax",
106 "lock.*security",
107 "ma[il1]{1}[ -]?box.*quo",
108 "ma[il1]{2}[ -]?box.*fu[il1]",
109 "ma[il1]{2}box.*[il1]{2}mit",
110 "ma[il1]{2}box stor",
111 "mail on.?hold",
112 "mail.*box.*migration",
113 "mail.*de-?activat",
114 "mail.update.required",
115 "mails.*pending",
116 "messages.*pending",
117 "missed.*shipping.*notification",
118 "missed.shipment.notification",
119 "must.update.your.account",
120 "new [sl][io]g?[nig][ -]?in from",
121 "new voice ?-?mail",
122 "notifications.*pending",
123 "office.*3.*6.*5.*suspend",
124 "office365",
125 "on google docs with you",
126 "online doc",
127 "password.*compromised",
128 "periodic maintenance",
129 "potential(ly)? unauthorized",
130 "refund not approved",
131 "revised.*policy",
132 "scam",
133 "scanned.?invoice",
134 "secured?.update",
135 "security breach",
136 "securlty",
137 "signed.*delivery",
138 "status of your .{314}? ?delivery",
139 "susp[il1]+c[il1]+ous.*act[il1]+v[il1]+ty",
140 "suspicious.*sign.*[io]n",
141 "suspicious.activit",
142 "temporar(il)?y deactivate",
143 "temporar[il1]{2}y disab[li]ed",
144 "temporarily.*lock",
145 "un-?usua[li].activity",
146 "unable.*deliver",
147 "unauthorized.*activit",
148 "unauthorized.device",
149 "unauthorized.sign.?in",
150 "unrecognized.*activit",
151 "unrecognized.sign.?in",
152 "unrecognized.*activit",
153 "undelivered message",
154 "unread.*doc",
155 "unusual.activity",
156 "upgrade.*account",
157 "upgrade.notice",
158 "urgent message",
159 "urgent.verification",
160 "v[il1]o[li1]at[il1]on security",
161 "va[il1]{1}date.*ma[il1]{2}[ -]?box",
162 "verification ?-?require",
163 "verification( )?-?need",
164 "verify.your?.account",
165 "web ?-?ma[il1]{2}",
166 "web[ -]?ma[il1]{2}",
167 "will.be.suspended",
168 "your (customer )?account .as",
169 "your.office.365",
170 "your.online.access",
171
172 // https://github.com/sublime-security/static-files/blob/master/suspicious_subjects.txt
173 "account has been limited",
174 "action required",
175 "almost full",
176 "apd notifi cation",
177 "are you at your desk",
178 "are you available",
179 "attached file to docusign",
180 "banking is temporarily unavailable",
181 "bankofamerica",
182 "closing statement invoice",
183 "completed: docusign",
184 "de-activation of",
185 "delivery attempt",
186 "delivery stopped for shipment",
187 "detected suspicious",
188 "detected suspicious actvity",
189 "docu sign",
190 "document for you",
191 "document has been sent to you via docusign",
192 "document is ready for signature",
193 "docusign",
194 "encrypted message",
195 "failed delivery",
196 "fedex tracking",
197 "file was shared",
198 "freefax",
199 "fwd: due invoice paid",
200 "has shared",
201 "inbox is full",
202 "invitation to comment",
203 "invitation to edit",
204 "invoice due",
205 "left you a message",
206 "message from",
207 "new message",
208 "new voicemail",
209 "on desk",
210 "out of space",
211 "password reset",
212 "payment status",
213 "quick reply",
214 "re: w-2",
215 "required",
216 "required: completed docusign",
217 "ringcentral",
218 "scanned image",
219 "secured files",
220 "secured pdf",
221 "security alert",
222 "new sign-in",
223 "new sign in",
224 "sign-in attempt",
225 "sign in attempt",
226 "staff review",
227 "suspicious activity",
228 "unrecognized login attempt",
229 "upgrade immediately",
230 "urgent",
231 "wants to share",
232 "w2",
233 "you have notifications pending",
234 "your account",
235 "your amazon order",
236 "your document settlement",
237 "your order with amazon",
238 "your password has been compromised",
239 )
240
241 // language attempting to engage
242 and any(ml.nlu_classifier(body.current_thread.text).entities,
243 .name == "request"
244 )
245
246 // financial request
247 and any(ml.nlu_classifier(body.current_thread.text).entities,
248 .name == "financial"
249 )
250
251 // urgency request
252 and any(ml.nlu_classifier(body.current_thread.text).entities,
253 .name == "urgency"
254 )
255
256 // org presence
257 and any(ml.nlu_classifier(body.current_thread.text).entities, .name == "org")
258
259 // not a reply
260 and (
261 not strings.istarts_with(subject.subject, "re:")
262 and not any(headers.hops, any(.fields, strings.ilike(.name, "In-Reply-To")))
263 )
264
265 // the message is unsolicited and no false positives
266 and (
267 not profile.by_sender().solicited
268 or profile.by_sender().any_messages_malicious_or_spam
269 )
270 and not profile.by_sender().any_false_positives
271
272 // negate highly trusted sender domains unless they fail DMARC authentication
273 and (
274 (
275 sender.email.domain.root_domain in $high_trust_sender_root_domains
276 and not headers.auth_summary.dmarc.pass
277 )
278 or sender.email.domain.root_domain not in $high_trust_sender_root_domains
279 )
280
281 // negation the only link is the senders email
282 and not (
283 regex.contains(body.current_thread.text,
284 "[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,}"
285 )
286 and (
287 all(body.links, .href_url.domain.root_domain == sender.email.domain.domain)
288 )
289 )
290
291attack_types:
292 - "Credential Phishing"
293tactics_and_techniques:
294 - "Impersonation: Brand"
295 - "Social engineering"
296detection_methods:
297 - "Content analysis"
298 - "Header analysis"
299 - "Natural Language Understanding"
300 - "Sender analysis"
301id: "056464f4-7a16-5f07-ab86-912e0a64ecae"