Self Extracting Package Creation Via Iexpress.EXE From Potentially Suspicious Location

Severity: high
Author: Joseliyo Sanchez, @Joseliyo_Jstnk, Nasreddine Bencherchali (Nextron Systems)
Source: upstream

Detects the use of iexpress.exe to create binaries via Self Extraction Directive (SED) files located in potentially suspicious locations. This behavior has been observed in-the-wild by different threat actors.

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: '\iexpress.exe'
OriginalFileName: IEXPRESS.exe

Stage 2: `all of selection_cli`

CommandLine|contains: ' /n '

Stage 3: `all of selection_paths`

or:
CommandLine|contains: ':\ProgramData\'
CommandLine|contains: ':\Temp\'
CommandLine|contains: ':\Windows\System32\Tasks\'
CommandLine|contains: ':\Windows\Tasks\'
CommandLine|contains: ':\Windows\Temp\'
CommandLine|contains: '\AppData\Local\Temp\'

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	`/n` `:\ProgramData\` corpus 5 (sigma 5) `:\Temp\` corpus 14 (sigma 14) `:\Windows\System32\Tasks\` corpus 3 (sigma 3) `:\Windows\Tasks\` corpus 6 (sigma 6) `:\Windows\Temp\` corpus 15 (sigma 15) `\AppData\Local\Temp\` corpus 16 (sigma 16)
`Image`	ends_with	`\iexpress.exe`
`OriginalFileName`	eq	`IEXPRESS.exe`