Detection rules › Sublime MQL

Service abuse: DocSend share from an unsolicited reply-to address

Severity
high
Type
rule
Source
github.com/sublime-security/sublime-rules

DocSend shares which contain a reply-to address or domain that has not been previously observed by the recipient organization.

Threat classification

Sublime's own taxonomy (not MITRE ATT&CK).

CategoryValues
Attack typesCredential Phishing
Tactics and techniquesEvasion, Free file host, Social engineering

Event coverage

Message attribute
sender.email
type

Rule body MQL

type.inbound

// Legitimate DocSend sending infratructure
and sender.email.email == "no-reply@docsend.com"

// 
// This rule makes use of a beta feature and is subject to change without notice
// using the beta feature in custom rules is not suggested until it has been formally released
// 

// reply-to address has never sent an email to the org
and beta.profile.by_reply_to().prevalence == "new"

// reply-to email address has never been sent an email by the org
and not beta.profile.by_reply_to().solicited

// do not match if the reply_to address has been observed as a reply_to address
// of a message that has been classified as benign
and not beta.profile.by_reply_to().any_messages_benign

Detection logic

Scope: inbound message.

DocSend shares which contain a reply-to address or domain that has not been previously observed by the recipient organization.

  1. inbound message
  2. sender.email.email is 'no-reply@docsend.com'
  3. beta.profile.by_reply_to().prevalence is 'new'
  4. not:
    • beta.profile.by_reply_to().solicited
  5. not:
    • beta.profile.by_reply_to().any_messages_benign

Inspects: sender.email.email, type.inbound. Sensors: beta.profile.by_reply_to.

Indicators matched (1)

FieldMatchValue
sender.email.emailequalsno-reply@docsend.com