Suspicious DLL Loaded via CertOC.EXE

Severity: high
Author: Nasreddine Bencherchali (Nextron Systems)
Source: upstream

Detects when a user installs certificates by using CertOC.exe to load the target DLL file.

MITRE ATT&CK coverage

Tactic	Techniques
Defense Evasion	`T1218` System Binary Proxy Execution

Event coverage

Provider	Event ID	Title
Sysmon	1	Process creation

Stages and Predicates

Stage 1: `all of selection_img`

or:
Image|endswith: '\certoc.exe'
OriginalFileName: CertOC.exe

Stage 2: `all of selection_cli`

CommandLine|contains: ' -LoadDLL '

Stage 3: `all of selection_paths`

or:
CommandLine|contains: 'C:\Windows\Tasks\'
CommandLine|contains: 'C:\Windows\Temp\'
CommandLine|contains: '\Appdata\Local\Temp\'
CommandLine|contains: '\Desktop\'
CommandLine|contains: '\Downloads\'
CommandLine|contains: '\Users\Public\'

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
`CommandLine`	match	`-LoadDLL` corpus 2 (sigma 2) `C:\Windows\Tasks\` `C:\Windows\Temp\` corpus 4 (sigma 4) `\Appdata\Local\Temp\` corpus 2 (sigma 2) `\Desktop\` corpus 11 (sigma 11) `\Downloads\` corpus 12 (sigma 12) `\Users\Public\` corpus 17 (sigma 17)
`Image`	ends_with	`\certoc.exe` corpus 10 (sigma 10)
`OriginalFileName`	eq	`CertOC.exe` corpus 6 (sigma 6)