T1036.007 Double File Extension

Technique: T1036.007
Tactics: Defense Evasion
Research, 90 days: 1
KEV CVEs mapped: 0
SigmaHQ rules: 3
Elastic, Splunk: 1
thrunt rules: 0
Upstream: https://attack.mitre.org/techniques/T1036/007

MITRE description

Adversaries may abuse a double extension in the filename as a means of masquerading the true file type. A file name may include a secondary file type extension that may cause only the first extension to be displayed (ex: <code>File.txt.exe</code> may render in some views as just <code>File.txt</code>). However, the second extension is the true file type that determines how the file is opened and executed. The real file extension may be hidden by the operating system in the file browser (ex: explorer.exe), as well as in any software configured using or similar to the system’s policies.(Citation: PCMag DoubleExtension)(Citation: SOCPrime DoubleExtension) Adversaries may abuse double extensions to attempt to conceal dangerous file types of payloads. A very common usage involves tricking a user into opening what they think is a benign file type but is actually executable code. Such files often pose as email attachments and allow an adversary to gain [Initial Access](https://attack.mitre.org/tactics/TA0001) into a user’s system via [Spearphishing Attachment](https://attack.mitre.org/techniques/T1566/001) then [User Execution](https://attack.mitre.org/techniques/T1204). For example, an executable file attachment named <code>Evil.txt.exe</code> may display as <code>Evil.txt</code> to a user. The user may then view it as a benign text file and open it, inadvertently executing the hidden malware.(Citation: SOCPrime DoubleExtension) Common file types, such as text files (.txt, .doc, etc.) and image files (.jpg, .gif, etc.) are typically used as the first extension to appear benign. Executable extensions commonly regarded as dangerous, such as .exe, .lnk, .hta, and .scr, often appear as the second extension and true file type.

Research citing this technique

Reports and advisories from the last 90 days that cite this technique.

2026-10-30 Darktrace: CikaBika Bot: Inside a Discord RAT Campaign

Detection coverage

SigmaHQ community rules

Suspicious Double Extension Files (core)
Suspicious LNK Double Extension File Created (core)
Suspicious Parent Double Extension File Execution (core)

Elastic and Splunk rules

Executable File Creation with Multiple Extensions (elastic)

Signal counts reflect the current corpus snapshot. Research citations are the technique IDs named in vendor reports and government advisories from the last 90 days; KEV mappings come from MITRE CTID. Coverage is the SigmaHQ rule inventory (core, emerging-threats, threat-hunting) at release r2026-07-01 plus Elastic and Splunk production rules. Rule bodies are not mirrored; links go upstream.