Potential Initial Access via DLL Search Order Hijacking

Severity: medium
Author: Tim Rauch (rule), Elastic (idea)
Source: upstream

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.

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1566` Phishing, `T1566.001` Phishing: Spearphishing Attachment
Persistence	`T1574` Hijack Execution Flow, `T1574.001` Hijack Execution Flow: DLL
Privilege Escalation	`T1574` Hijack Execution Flow, `T1574.001` Hijack Execution Flow: DLL
Defense Evasion	`T1574` Hijack Execution Flow, `T1574.001` Hijack Execution Flow: DLL

Event coverage

Provider	Event ID	Title
Sysmon	11	FileCreate

Stages and Predicates

Stage 1: `selection`

or:
Image|endswith: '\MSACCESS.EXE'
Image|endswith: '\MSPUB.EXE'
Image|endswith: '\certutil.exe'
Image|endswith: '\cmd.exe'
Image|endswith: '\cscript.exe'
Image|endswith: '\curl.exe'
Image|endswith: '\excel.exe'
Image|endswith: '\fltldr.exe'
Image|endswith: '\mshta.exe'
Image|endswith: '\powerpnt.exe'
Image|endswith: '\powershell.exe'
Image|endswith: '\pwsh.exe'
Image|endswith: '\winword.exe'
Image|endswith: '\wscript.exe'
or:
TargetFilename|contains: '\Local\Programs\Microsoft VS Code\'
TargetFilename|contains: '\Local\slack\app-'
TargetFilename|contains: '\Microsoft OneDrive\'
TargetFilename|contains: '\Microsoft\OneDrive\'
TargetFilename|contains: '\Microsoft\Teams\'
TargetFilename|endswith: .dll
TargetFilename|contains: '\AppData\'
TargetFilename|contains: '\Users\'

Stage 2: `not filter`

Image|endswith: '\cmd.exe'
TargetFilename|contains: '\AppData\'
TargetFilename|contains: '\Microsoft\OneDrive\'
TargetFilename|contains: '\Users\'
TargetFilename|contains: '\api-ms-win-core-'

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`Image`	ends_with	`\MSACCESS.EXE` `\MSPUB.EXE` corpus 2 (sigma 2) `\certutil.exe` corpus 34 (sigma 34) `\cmd.exe` corpus 92 (sigma 92) `\cscript.exe` corpus 64 (sigma 64) `\curl.exe` corpus 19 (sigma 19) `\excel.exe` corpus 16 (sigma 16) `\fltldr.exe` `\mshta.exe` corpus 57 (sigma 57) `\powerpnt.exe` corpus 13 (sigma 13) `\powershell.exe` corpus 143 (sigma 143) `\pwsh.exe` corpus 140 (sigma 140) `\winword.exe` corpus 17 (sigma 17) `\wscript.exe` corpus 64 (sigma 64)
`TargetFilename`	ends_with	`.dll` corpus 21 (sigma 21)
`TargetFilename`	match	`\AppData\` corpus 3 (sigma 3) `\Local\Programs\Microsoft VS Code\` `\Local\slack\app-` `\Microsoft OneDrive\` `\Microsoft\OneDrive\` `\Microsoft\Teams\` `\Users\` corpus 2 (sigma 2) `\api-ms-win-core-`