Email Collection: Email Forwarding Rule T1114.003
Tactic: Collection
Adversaries may setup email forwarding rules to collect sensitive information. Adversaries may abuse email forwarding rules to monitor the activities of a victim, steal information, and further gain intelligence on the victim or the victim’s organization to use as part of further exploits or operations. Furthermore, email forwarding rules can allow adversaries to maintain persistent access to victim's emails even after compromised credentials are reset by administrators. Most email clients allow users to create inbox rules for various email functions, including forwarding to a different recipient. These rules may be created through a local email application, a web interface, or by command-line interface. Messages can be forwarded to internal or external recipients, and there are no restrictions limiting the extent of this rule. Administrators may also create forwarding rules for user accounts with the same considerations and outcomes.
Events covered
1 catalog event is tagged with this technique by at least one rule.
| Provider | Event | Title |
|---|---|---|
| PowerShell | Event ID 4104 | Creating Scriptblock text (MessageNumber of MessageTotal). |
Authoring guide
Patterns shared across the 16 rules above: which fields they filter on, what specific values they look for, and what they exclude. The catalog normalizes field names across vendors so Sigma's Image, Elastic's process.name, and Splunk's process_name collapse into one row. Each rule contributes at most once per row.
Fields filtered most (32 distinct)
The fields most rules look at when detecting this technique. The How column shows the operators authors use (eq, wildcard, regex_match, match) and how often each appears. Sample values are concrete examples to start from, not an exhaustive list.
Top indicator values (78 distinct)
Specific (field, operator, value) combinations the rules check for, ranked by how many rules under this technique use each one. The Corpus reach column counts how many rules across the entire catalog (any technique) check the same combination. High numbers point to widely-used indicators that are likely noisy on their own; combine them with another condition for useful signal. Blank means the combination is specific to rules under this technique. Click a value to expand the rules under this technique that use it.
Rules under this technique
Every rule in the catalog tagged with this technique, grouped by vendor. Click a rule title for its full predicates, exclusions, and indicators.
Sigma 6 rules
- Google Workspace Out Of Domain Email Forwarding
- Inbox Rules Creation Or Update Activity in O365
- Inbox Rules Creation Or Update Activity Via ExchangePowerShell Cmdlet
- Mail Forwarding/Redirecting Activity In O365
- Mail Forwarding/Redirecting Activity Via ExchangePowerShell Cmdlet
- Suspicious Inbox Forwarding Identity Protection
Elastic 3 rules
- Google Workspace Custom Gmail Route Created or Modified
- M365 Exchange Inbox Forwarding Rule Created
- M365 Exchange Mail Flow Transport Rule Created
Splunk 6 rules
- O365 Email New Inbox Rule Created
- O365 Email Suspicious Behavior Alert
- O365 Email Transport Rule Changed
- O365 Mailbox Email Forwarding Enabled
- O365 New Email Forwarding Rule Created
- O365 New Email Forwarding Rule Enabled