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ATT&CK techniqueInitial Access

T1566.001 Spearphishing Attachment

Initial AccessEnterpriseSub-technique

As of 2026-10-05, T1566.001 (Spearphishing Attachment) appears in 194 tracked threats, first reported 2026-01-14 and most recently 2026-10-02, with linked actors including APT28, Forest Blizzard, APT36; it most often appears alongside T1204.002 (Malicious File).

Tracked threats
19423 critical, 147 high, 24 medium
First seen
2026-01-14
Last seen
2026-10-02
Threat actors
83In the threats using it
Detection rules
465Blue tier and above

Data as of:

Activity timeline

T1566.001 first appeared in tracked threats on and was most recently reported on . The busiest month was 2026-07 with 61 reports, and 194 of the 194 threats were reported in the twelve months to 2026-10.

How adversaries use it

T1566.001 Spearphishing Attachment is catalogued by MITRE ATT&CK under the Initial Access tactic in the Enterprise matrix, as a sub-technique of T1566 Phishing. Threadlinqs maps 194 of 2623 tracked threats (7.4%) to it; by severity that is 23 critical, 147 high, 24 medium.

Threats that use T1566.001 most often also use T1204.002 Malicious File (159 threats), T1071.001 Web Protocols (128 threats), T1027 Obfuscated Files or Information (115 threats), T1082 System Information Discovery (105 threats), T1140 Deobfuscate/Decode Files or Information (96 threats). These are the techniques an intrusion set tends to chain with it, so they are the natural next places to look when it is observed.

83 tracked threat actors appear in the threats that use T1566.001; the most frequent are APT28 (12), Forest Blizzard (8), APT36 (6), APT43 (6), BlueDelta (6).

Mitigations

MITRE ATT&CK lists 7 mitigations for T1566.001.

Data sources

Telemetry that can reveal T1566.001, per MITRE ATT&CK.

  • Application Log — Application Log Content
  • File — File Creation
  • Network Traffic — Network Traffic Content, Network Traffic Flow

Threat actors using it

Tracked threats

The 30 most recent of 194 tracked threats that use T1566.001.

Detection coverage

Threadlinqs maintains 465 detection rules mapped to T1566.001 (SPL 184, KQL 131, Sigma 150). Rule content is available to Blue tier accounts and above; this page shows counts only.

465 detection rules (SPL/KQL/Sigma) · Blue and above. Compare plans

Parent technique

T1566 Phishing — 641 tracked threats at the technique level.