Detection rules › Sublime MQL
Credential phishing: Email delivery failure impersonation
Detects phishing emails impersonating email system notifications claiming delivery failures, rejected messages, or email system issues requiring user action to 'fix' or 'recover' email functionality. These attacks typically claim incoming emails couldn't be delivered and direct users to malicious portals to harvest credentials.
Threat classification
Sublime's own taxonomy (not MITRE ATT&CK).
| Category | Values |
|---|---|
| Attack types | Credential Phishing |
| Tactics and techniques | Impersonation: Brand, Social engineering |
Event coverage
Rule body MQL
type.inbound
and length(body.links) < 10
and (
any(ml.nlu_classifier(body.current_thread.text).intents,
.name == "cred_theft" and .confidence == "high"
)
or (
length(body.current_thread.text) < 250
and any(recipients.to,
strings.icontains(body.current_thread.text, .email.domain.sld)
or strings.icontains(body.current_thread.text, .email.local_part)
)
)
)
and (
regex.icontains(subject.subject, '(e)?mail(s)?')
or (
length(body.current_thread.text) < 700
and strings.ilike(body.current_thread.text, '*mail*')
)
)
and 3 of (
strings.ilike(body.current_thread.text, "*incoming messages*"),
strings.ilike(body.current_thread.text, "*server error*"),
strings.ilike(body.current_thread.text, "*blocked*"),
strings.ilike(body.current_thread.text, "*prevented*"),
strings.ilike(body.current_thread.text, "*notification*"),
strings.ilike(body.current_thread.text, "*fix email issues*"),
strings.ilike(body.current_thread.text, "*rejected*"),
strings.ilike(body.current_thread.text, "*recover and prevent*"),
strings.ilike(body.current_thread.text, "*failure*"),
strings.ilike(body.current_thread.text, "*rejection*"),
strings.ilike(body.current_thread.text, "*failed*")
)
and (
any(body.links,
regex.icontains(.display_text,
"view",
"messages",
"recover",
"fix",
"portal",
"connect"
)
and not .display_text == "View Report"
and .href_url.domain.root_domain in ("gmass.co")
)
or (
length(body.links) < 3
and any(body.links,
any(recipients.to,
.email.domain.root_domain == ..display_url.domain.root_domain
and ..mismatched
)
)
)
or (all(recipients.to, .email.local_part == sender.display_name))
or any(body.links,
any(.href_url.rewrite.encoders, . == "proofpoint")
and .href_url.domain.root_domain not in $tranco_50k
and .href_url.domain.root_domain not in $org_domains
)
)
and not any(body.links,
regex.icontains(.display_text,
"view document",
"review (&|and) sign document"
)
)
and sender.email.domain.root_domain not in (
"bing.com",
"microsoft.com",
"microsoftonline.com",
"microsoftsupport.com",
"microsoft365.com",
"office.com",
"office365.com",
"onedrive.com",
"sharepointonline.com",
"yammer.com",
"ppops.net"
)
// negate org domains unless they fail DMARC authentication
and (
(
sender.email.domain.root_domain in $org_domains
and (
not headers.auth_summary.dmarc.pass
// MS emails from an org domain are router "internally" to MS, therefore, there is no authentication information
or not (
headers.auth_summary.dmarc.pass is null
and all(headers.domains,
.root_domain in ("outlook.com", "office365.com")
)
// typical emails from freemail Outlook accounts are from prod.outlook.com
and strings.ends_with(headers.message_id, "protection.outlook.com>")
)
)
)
or sender.email.domain.root_domain not in $org_domains
)
// negate highly trusted sender domains unless they fail DMARC authentication
and (
(
sender.email.domain.root_domain in $high_trust_sender_root_domains
and not headers.auth_summary.dmarc.pass
)
or sender.email.domain.root_domain not in $high_trust_sender_root_domains
)
and not profile.by_sender().solicited
and not profile.by_sender().any_messages_benign
Detection logic
Scope: inbound message.
Detects phishing emails impersonating email system notifications claiming delivery failures, rejected messages, or email system issues requiring user action to 'fix' or 'recover' email functionality. These attacks typically claim incoming emails couldn't be delivered and direct users to malicious portals to harvest credentials.
- inbound message
- length(body.links) < 10
any of:
any of
ml.nlu_classifier(body.current_thread.text).intentswhere all hold:- .name is 'cred_theft'
- .confidence is 'high'
all of:
- length(body.current_thread.text) < 250
any of
recipients.towhere any holds:- strings.icontains(body.current_thread.text)
- strings.icontains(body.current_thread.text)
any of:
- subject.subject matches '(e)?mail(s)?'
all of:
- length(body.current_thread.text) < 700
- body.current_thread.text matches '*mail*'
at least 3 of 11: body.current_thread.text matches any of 11 patterns
*incoming messages**server error**blocked**prevented**notification**fix email issues**rejected**recover and prevent**failure**rejection**failed*
any of:
any of
body.linkswhere all hold:.display_text matches any of 6 patterns
viewmessagesrecoverfixportalconnect
not:
- .display_text is 'View Report'
- .href_url.domain.root_domain in ('gmass.co')
all of:
- length(body.links) < 3
any of
body.linkswhere:any of
recipients.towhere all hold:- .email.domain.root_domain is .display_url.domain.root_domain
- .mismatched
all of
recipients.towhere:- .email.local_part is sender.display_name
any of
body.linkswhere all hold:any of
.href_url.rewrite.encoderswhere:- . is 'proofpoint'
- .href_url.domain.root_domain not in $tranco_50k
- .href_url.domain.root_domain not in $org_domains
not:
any of
body.linkswhere:.display_text matches any of 2 patterns
view documentreview (&|and) sign document
- sender.email.domain.root_domain not in ('bing.com', 'microsoft.com', 'microsoftonline.com', 'microsoftsupport.com', 'microsoft365.com', 'office.com', 'office365.com', 'onedrive.com', 'sharepointonline.com', 'yammer.com', 'ppops.net')
any of:
all of:
- sender.email.domain.root_domain in $org_domains
any of:
not:
- headers.auth_summary.dmarc.pass
not:
all of:
- headers.auth_summary.dmarc.pass is missing
all of
headers.domainswhere:- .root_domain in ('outlook.com', 'office365.com')
- headers.message_id ends with 'protection.outlook.com>'
- sender.email.domain.root_domain not in $org_domains
any of:
all of:
- sender.email.domain.root_domain in $high_trust_sender_root_domains
not:
- headers.auth_summary.dmarc.pass
- sender.email.domain.root_domain not in $high_trust_sender_root_domains
not:
- profile.by_sender().solicited
not:
- profile.by_sender().any_messages_benign
Inspects: body.current_thread.text, body.links, body.links[].display_text, body.links[].display_url.domain.root_domain, body.links[].href_url.domain.root_domain, body.links[].href_url.rewrite.encoders, body.links[].mismatched, headers.auth_summary.dmarc.pass, headers.domains, headers.domains[].root_domain, headers.message_id, recipients.to, recipients.to[].email.domain.root_domain, recipients.to[].email.domain.sld, recipients.to[].email.local_part, sender.display_name, sender.email.domain.root_domain, subject.subject, type.inbound. Sensors: ml.nlu_classifier, profile.by_sender, regex.icontains, strings.ends_with, strings.icontains, strings.ilike. Reference lists: $high_trust_sender_root_domains, $org_domains, $tranco_50k.
Indicators matched (40)
| Field | Match | Value |
|---|---|---|
ml.nlu_classifier(body.current_thread.text).intents[].name | equals | cred_theft |
ml.nlu_classifier(body.current_thread.text).intents[].confidence | equals | high |
regex.icontains | regex | (e)?mail(s)? |
strings.ilike | substring | *mail* |
strings.ilike | substring | *incoming messages* |
strings.ilike | substring | *server error* |
strings.ilike | substring | *blocked* |
strings.ilike | substring | *prevented* |
strings.ilike | substring | *notification* |
strings.ilike | substring | *fix email issues* |
strings.ilike | substring | *rejected* |
strings.ilike | substring | *recover and prevent* |
28 more
strings.ilike | substring | *failure* |
strings.ilike | substring | *rejection* |
strings.ilike | substring | *failed* |
regex.icontains | regex | view |
regex.icontains | regex | messages |
regex.icontains | regex | recover |
regex.icontains | regex | fix |
regex.icontains | regex | portal |
regex.icontains | regex | connect |
body.links[].display_text | equals | View Report |
body.links[].href_url.domain.root_domain | member | gmass.co |
body.links[].href_url.rewrite.encoders[] | equals | proofpoint |
regex.icontains | regex | view document |
regex.icontains | regex | review (&|and) sign document |
sender.email.domain.root_domain | member | bing.com |
sender.email.domain.root_domain | member | microsoft.com |
sender.email.domain.root_domain | member | microsoftonline.com |
sender.email.domain.root_domain | member | microsoftsupport.com |
sender.email.domain.root_domain | member | microsoft365.com |
sender.email.domain.root_domain | member | office.com |
sender.email.domain.root_domain | member | office365.com |
sender.email.domain.root_domain | member | onedrive.com |
sender.email.domain.root_domain | member | sharepointonline.com |
sender.email.domain.root_domain | member | yammer.com |
sender.email.domain.root_domain | member | ppops.net |
headers.domains[].root_domain | member | outlook.com |
headers.domains[].root_domain | member | office365.com |
strings.ends_with | suffix | protection.outlook.com> |