Creation of WerFault.exe/Wer.dll in Unusual Folder

Severity: medium
Author: frack113
Source: upstream

Detects the creation of a file named "WerFault.exe" or "wer.dll" in an uncommon folder, which could be a sign of WerFault DLL hijacking.

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1574.001` Hijack Execution Flow: DLL
Privilege Escalation	`T1574.001` Hijack Execution Flow: DLL
Defense Evasion	`T1574.001` Hijack Execution Flow: DLL

Event coverage

Provider	Event ID	Title
Sysmon	11	FileCreate

Stages and Predicates

Stage 1: `selection`

or:
TargetFilename|endswith: '\WerFault.exe'
TargetFilename|endswith: '\wer.dll'

Stage 2: `not 1 of filter_main_known_locations`

or:
TargetFilename|startswith: 'C:\Windows\SoftwareDistribution\'
TargetFilename|startswith: 'C:\Windows\SysWOW64\'
TargetFilename|startswith: 'C:\Windows\System32\'
TargetFilename|startswith: 'C:\Windows\UUS\arm64\'
TargetFilename|startswith: 'C:\Windows\WinSxS\'

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
`TargetFilename`	ends_with	`\WerFault.exe` corpus 2 (sigma 2) `\wer.dll`
`TargetFilename`	starts_with	`C:\Windows\SoftwareDistribution\` `C:\Windows\SysWOW64\` corpus 2 (sigma 2) `C:\Windows\System32\` corpus 3 (sigma 3) `C:\Windows\UUS\arm64\` `C:\Windows\WinSxS\` corpus 2 (sigma 2)