Techniques › T1566 › T1566.003
T1566.003 Spearphishing via Service
initial access — Linux, macOS, Windows · attack.mitre.org · JSON
1
MITRE detection strategy
3
analytics
0
Sigma rules tagged attack.t1566.003
0
KEV CVEs mapped here
<p>Adversaries may send spearphishing messages via third-party services in an attempt to gain access to victim systems. Spearphishing via service is a specific variant of spearphishing. It is different from other forms of spearphishing in that it employs the use of third party services rather than directly via enterprise email channels.</p><p>All forms of spearphishing are electronically delivered social engineering targeted at a specific individual, company, or industry. In this scenario, adversaries send messages through various social media services, personal webmail, and other non-enterprise controlled services. These services are more likely to have a less-strict security policy than an enterprise. As with most kinds of spearphishing, the goal is to generate rapport with the target or get the target's interest in some way. Adversaries will create fake social media accounts and message employees for potential job opportunities. Doing so allows a plausible reason for asking about services, policies, and software that's running in an environment. The adversary can then send malicious links or attachments through these services.</p><p>A common example is to build rapport with a target via social media, then send content to a personal webmail service that the target uses on their work computer. This allows an adversary to bypass some email restrictions on the work account, and the target is more likely to open the file since it's something they were expecting. If the payload doesn't work as expected, the adversary can continue normal communications and troubleshoot with the target on how to get it working.</p>
KEV CVEs mapped to this technique · CTID Mappings Explorer
None. No KEV entry in the public mapping names this technique. Given that 74.7% of KEV has no mapping at all, this says more about the mapping than about the technique.
Detection strategy · ATT&CK Enterprise v19.2
- DET0115 Detection Strategy for Spearphishing via a Service across OS Platforms v1.0
AN0320 WindowsInbound spearphishing attempts delivered via third-party services (e.g., Gmail, LinkedIn messages) leading to malicious file downloads or browser-initiated script execution. Defender view includes correlation of external service logins, unexpected file write operations, and suspicious descendant processes spawned from productivity or browser applications.Tunable:
MonitoredServicesSuspiciousProcessPatternsTimeWindowAN0321 LinuxUse of non-enterprise email or messaging services in Thunderbird, Evolution, or browsers leading to suspicious file downloads and subsequent execution. Defender view includes browser-initiated downloads of unexpected content and shell or interpreter processes launched post-download.auditd:SYSCALLexecve: Execution of bash, python, or perl processes spawned by browser/email client→ DC0032 Process Creationlinux:syslogInbound messages from webmail services containing attachments or URLs→ DC0038 Application Log ContentNSM:FlowOutbound traffic to domains/IPs not previously resolved, occurring shortly after attachment download or link click→ DC0078 Network Traffic FlowTunable:BrowserProcessesPhishingIndicatorsAN0322 macOSPhishing attempts via iCloud Mail, Gmail, or social media apps accessed on macOS systems. Defender view includes Mail.app or Safari downloads of files followed by osascript, Terminal, or abnormal child process execution.macos:unifiedlogReceived messages containing embedded links or attachments from non-enterprise services→ DC0038 Application Log Contentmacos:unifiedlogExecution of osascript, bash, or Terminal initiated from Mail.app or Safari→ DC0032 Process Creationmacos:unifiedlogSuspicious outbound HTTPS requests to domains flagged as newly registered or untrusted after spearphishing message interaction→ DC0085 Network Traffic ContentTunable:CertificateChecksExecutionDelay
Sigma rules · SigmaHQ da9bb07d64, tag attack.t1566.003
No Sigma rule carries this tag. MITRE publishes a detection strategy above, so the behaviour is specified; what is missing is public detection content.
Rules tagged at the parent level (attack.t1566) 14
These target the parent technique, not this sub-technique specifically. Listed for completeness, not counted as coverage.
Author: Florian Roth (Nextron Systems)
· 2017-11-07 (modified 2023-05-18) · logsource: category=proxy · 00d0b5ab-1f55-4120-8e83-487c0a7baf19
Detects download of certain file types from hosts in suspicious TLDs
Author: Ahmed Farouk
· 2024-05-10 · logsource: category=proxy · 1ae64f96-72b6-48b3-ad3d-e71dff6c6398
Detects executables launched from external WebDAV shares using the WebDAV Explorer integration, commonly seen in initial access campaigns.
Author: Sittikorn S, frack113
· 2021-07-16 (modified 2023-08-17) · logsource: product=windows category=registry_set · 32b5db62-cb5f-4266-9639-0fa48376ac00
Detects patterns as noticed in exploitation of Windows CVE-2021-31979 CVE-2021-33771 vulnerability and DevilsTongue malware by threat group Sourgum
Author: jamesc-grafana
· 2024-07-11 (modified 2025-12-08) · logsource: product=aws service=cloudtrail · 38e7f511-3f74-41d4-836e-f57dfa18eead
Detect when System Manager successfully executes commands against an instance.
Author: Micah Babinski
· 2023-08-21 · logsource: product=windows category=file_event · 4c55738d-72d8-490e-a2db-7969654e375f
Detects the creation of WebDAV temporary files with potentially suspicious extensions
Author: Maxim Pavlunin, Nasreddine Bencherchali (Nextron Systems)
· 2020-04-01 (modified 2023-04-12) · logsource: product=windows category=process_creation · 52cad028-0ff0-4854-8f67-d25dfcbc78b4
Detects a suspicious child process of a Microsoft HTML Help (HH.exe)
Author: Tim Rauch (rule), Elastic (idea)
· 2022-10-21 (modified 2022-12-28) · logsource: product=macos category=process_creation · 6e4dcdd1-e48b-42f7-b2d8-3b413fc58cb4
Detects when the macOS Script Editor utility spawns an unusual child process.
Author: Sittikorn S
· 2021-07-16 (modified 2022-10-09) · logsource: product=windows category=file_event · ad7085ac-92e4-4b76-8ce2-276d2c0e68ef
Detects patterns as noticed in exploitation of Windows CVE-2021-31979 CVE-2021-33771 vulnerability and DevilsTongue malware by threat group Sourgum
Author: Florian Roth (Nextron Systems)
· 2017-03-13 (modified 2023-05-18) · logsource: category=proxy · b5de2919-b74a-4805-91a7-5049accbaefe
Detects executable downloads from suspicious remote systems
Author: Tim Rauch (Nextron Systems), Nasreddine Bencherchali (Nextron Systems), Elastic (idea)
· 2022-10-21 (modified 2023-02-10) · logsource: product=windows category=process_creation · c27515df-97a9-4162-8a60-dc0eeb51b775
Detects suspicious child processes of the Microsoft OneNote application. This may indicate an attempt to execute malicious embedded objects from a .one file.
Author: Tim Rauch (rule), Elastic (idea)
· 2022-10-21 · logsource: product=windows category=file_event · dbbd9f66-2ed3-4ca2-98a4-6ea985dd1a1c
Detects attempts to create a DLL file to a known desktop application dependencies folder such as Slack, Teams or OneDrive and by an unusual process. This may indicate an attempt to load a malicious module via DLL search order hijacking.
Author: Maxim Pavlunin
· 2020-04-01 (modified 2023-04-12) · logsource: product=windows category=process_creation · e8a95b5e-c891-46e2-b33a-93937d3abc31
Detects a suspicious execution of a Microsoft HTML Help (HH.exe)
Author: Austin Songer @austinsonger
· 2023-05-07 (modified 2026-04-27) · logsource: product=okta service=okta · ee39a9f7-5a79-4b0a-9815-d36b3cf28d3e
Detects when Okta FastPass prevents a known phishing site.
Author: Florian Roth (Nextron Systems)
· 2022-06-07 · logsource: product=windows category=process_creation · fcdf69e5-a3d3-452a-9724-26f2308bf2b1
Detects cases in which an ISO files is opend within an archiver like 7Zip or Winrar, which is a sign of phishing as threat actors put small ISO files in archives as email attachments to bypass certain filters and protective measures (mark of web)