Windows Winword.exe Creates INetCache .cab and .inf Files During CVE-2021-40444 Exploitation
Flags winword.exe writing CABs in INetCache or INF files in Temp consistent with CVE-2021-40444 exploitation.
- Product
- windows
- Category
- file_event
- Author
- Florian Roth (Nextron Systems), Sittikorn S (SigmaHQ), DRL 1.1
- Published
- 2021-09-10
- Updated
- 2026-07-31
ATT&CK techniques
Resource DevRecon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
Cred Access
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact
What it detects
This rule flags Windows file creation activity where winword.exe writes a .cab file into the INetCache directory or creates a .inf file under AppData\Local\Temp. Such patterns can indicate document-triggered payload staging, where attacker-controlled files are dropped to transient locations for follow-on execution. It relies on file event telemetry capturing the process image path and the created target filename, including directory and extension details.
Reporting behind it
Changelog
v5- v5Candidate ingested via manual entry.2026-07-31
- v4Candidate ingested via manual entry.2026-07-31
- v3Candidate ingested via manual entry.2026-07-31
- v2Candidate ingested via manual entry.2026-07-31
- v1No changelog recorded for this version.2026-07-30
Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.
title: Windows Winword.exe Creates INetCache .cab and .inf Files During CVE-2021-40444 Exploitation
id: a88f0ba1-b2fc-47e3-a46d-000884918119
status: test
description: This rule flags Windows file creation activity where winword.exe writes a .cab file into the INetCache directory or creates a .inf file under AppData\Local\Temp. Such patterns can indicate document-triggered payload staging, where attacker-controlled files are dropped to transient locations for follow-on execution. It relies on file event telemetry capturing the process image path and the created target filename, including directory and extension details.
references:
- https://twitter.com/RonnyTNL/status/1436334640617373699?s=20
- https://twitter.com/vanitasnk/status/1437329511142420483?s=21
- https://github.com/SigmaHQ/sigma/blob/master/rules-emerging-threats/2021/Exploits/CVE-2021-40444/file_event_win_exploit_cve_2021_40444.yml
author: Florian Roth (Nextron Systems), Sittikorn S, Huntrule Team
date: 2021-09-10
modified: 2023-06-22
tags:
- attack.resource-development
- attack.t1587
- detection.emerging-threats
logsource:
product: windows
category: file_event
detection:
selection_cab:
Image|endswith: \winword.exe
TargetFilename|contains: \Windows\INetCache
TargetFilename|endswith: .cab
selection_inf:
Image|endswith: \winword.exe
TargetFilename|contains|all:
- \AppData\Local\Temp\
- ".inf"
filter_main_legit:
TargetFilename|startswith: C:\Users\
TargetFilename|contains: AppData\Local\Temp
TargetFilename|endswith: \Content.inf
condition: 1 of selection_* and not 1 of filter_main_*
falsepositives:
- Unknown
level: high
license: DRL-1.1
related:
- id: 60c0a111-787a-4e8a-9262-ee485f3ef9d5
type: derived