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 "deactivation.*in.*progress",
81 "delivery.*attempt.*failed",
82 "document.received",
83 "documented.*shared.*with.*you",
84 "dropbox.*document",
85 "e-?ma[il1]+ .{010}suspen",
86 "e-?ma[il1]{1} user",
87 "e-?ma[il1]{2} acc",
88 "e-?ma[il1]{2}.*up.?grade",
89 "e.?ma[il1]{2}.*server",
90 "e.?ma[il1]{2}.*suspend",
91 "email.update",
92 "faxed you",
93 "fraud(ulent)?.*charge",
94 "from.helpdesk",
95 "fu[il1]{2}.*ma[il1]+[ -]?box",
96 "has.been.*suspended",
97 "has.been.limited",
98 "have.locked",
99 "he[li]p ?desk upgrade",
100 "heipdesk",
101 "i[il]iega[il]",
102 "ii[il]ega[il]",
103 "incoming e?mail",
104 "incoming.*fax",
105 "lock.*security",
106 "ma[il1]{1}[ -]?box.*quo",
107 "ma[il1]{2}[ -]?box.*fu[il1]",
108 "ma[il1]{2}box.*[il1]{2}mit",
109 "ma[il1]{2}box stor",
110 "mail on.?hold",
111 "mail.*box.*migration",
112 "mail.*de-?activat",
113 "mail.update.required",
114 "mails.*pending",
115 "messages.*pending",
116 "missed.*shipping.*notification",
117 "missed.shipment.notification",
118 "must.update.your.account",
119 "new [sl][io]g?[nig][ -]?in from",
120 "new voice ?-?mail",
121 "notifications.*pending",
122 "office.*3.*6.*5.*suspend",
123 "office365",
124 "on google docs with you",
125 "online doc",
126 "password.*compromised",
127 "periodic maintenance",
128 "potential(ly)? unauthorized",
129 "refund not approved",
130 "revised.*policy",
131 "scam",
132 "scanned.?invoice",
133 "secured?.update",
134 "security breach",
135 "securlty",
136 "signed.*delivery",
137 "status of your .{314}? ?delivery",
138 "susp[il1]+c[il1]+ous.*act[il1]+v[il1]+ty",
139 "suspicious.*sign.*[io]n",
140 "suspicious.activit",
141 "temporar(il)?y deactivate",
142 "temporar[il1]{2}y disab[li]ed",
143 "temporarily.*lock",
144 "un-?usua[li].activity",
145 "unable.*deliver",
146 "unauthorized.*activit",
147 "unauthorized.device",
148 "unauthorized.sign.?in",
149 "unrecognized.*activit",
150 "unrecognized.sign.?in",
151 "unrecognized.*activit",
152 "undelivered message",
153 "unread.*doc",
154 "unusual.activity",
155 "upgrade.*account",
156 "upgrade.notice",
157 "urgent message",
158 "urgent.verification",
159 "v[il1]o[li1]at[il1]on security",
160 "va[il1]{1}date.*ma[il1]{2}[ -]?box",
161 "verification ?-?require",
162 "verification( )?-?need",
163 "verify.your?.account",
164 "web ?-?ma[il1]{2}",
165 "web[ -]?ma[il1]{2}",
166 "will.be.suspended",
167 "your (customer )?account .as",
168 "your.office.365",
169 "your.online.access",
170
171 // https://github.com/sublime-security/static-files/blob/master/suspicious_subjects.txt
172 "account has been limited",
173 "action required",
174 "almost full",
175 "apd notifi cation",
176 "are you at your desk",
177 "are you available",
178 "attached file to docusign",
179 "banking is temporarily unavailable",
180 "bankofamerica",
181 "closing statement invoice",
182 "completed: docusign",
183 "de-activation of",
184 "delivery attempt",
185 "delivery stopped for shipment",
186 "detected suspicious",
187 "detected suspicious actvity",
188 "docu sign",
189 "document for you",
190 "document has been sent to you via docusign",
191 "document is ready for signature",
192 "docusign",
193 "encrypted message",
194 "failed delivery",
195 "fedex tracking",
196 "file was shared",
197 "freefax",
198 "fwd: due invoice paid",
199 "has shared",
200 "inbox is full",
201 "invitation to comment",
202 "invitation to edit",
203 "invoice due",
204 "left you a message",
205 "message from",
206 "new message",
207 "new voicemail",
208 "on desk",
209 "out of space",
210 "password reset",
211 "payment status",
212 "quick reply",
213 "re: w-2",
214 "required",
215 "required: completed docusign",
216 "ringcentral",
217 "scanned image",
218 "secured files",
219 "secured pdf",
220 "security alert",
221 "new sign-in",
222 "new sign in",
223 "sign-in attempt",
224 "sign in attempt",
225 "staff review",
226 "suspicious activity",
227 "unrecognized login attempt",
228 "upgrade immediately",
229 "urgent",
230 "wants to share",
231 "w2",
232 "you have notifications pending",
233 "your account",
234 "your amazon order",
235 "your document settlement",
236 "your order with amazon",
237 "your password has been compromised",
238 )
239
240 // language attempting to engage
241 and any(ml.nlu_classifier(body.current_thread.text).entities,
242 .name == "request"
243 )
244
245 // financial request
246 and any(ml.nlu_classifier(body.current_thread.text).entities,
247 .name == "financial"
248 )
249
250 // urgency request
251 and any(ml.nlu_classifier(body.current_thread.text).entities,
252 .name == "urgency"
253 )
254
255 // org presence
256 and any(ml.nlu_classifier(body.current_thread.text).entities, .name == "org")
257
258 // not a reply
259 and (
260 not strings.istarts_with(subject.subject, "re:")
261 and not any(headers.hops, any(.fields, strings.ilike(.name, "In-Reply-To")))
262 )
263
264 // the message is unsolicited and no false positives
265 and (
266 not profile.by_sender().solicited
267 or profile.by_sender().any_messages_malicious_or_spam
268 )
269 and not profile.by_sender().any_false_positives
270
271 // negate highly trusted sender domains unless they fail DMARC authentication
272 and (
273 (
274 sender.email.domain.root_domain in $high_trust_sender_root_domains
275 and not headers.auth_summary.dmarc.pass
276 )
277 or sender.email.domain.root_domain not in $high_trust_sender_root_domains
278 )
279
280 // negation the only link is the senders email
281 and not (
282 regex.contains(body.current_thread.text,
283 "[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,}"
284 )
285 and (
286 all(body.links, .href_url.domain.root_domain == sender.email.domain.domain)
287 )
288 )
289
290attack_types:
291 - "Credential Phishing"
292tactics_and_techniques:
293 - "Impersonation: Brand"
294 - "Social engineering"
295detection_methods:
296 - "Content analysis"
297 - "Header analysis"
298 - "Natural Language Understanding"
299 - "Sender analysis"
300id: "056464f4-7a16-5f07-ab86-912e0a64ecae"