Spearphishing Attachment: ISO Images (Microsoft Defender for Endpoint)

Author: Cyb3rMonk
Source: github.com/Cyb3r-Monk/Threat-Hunting-and-Detection

ISO images are often meant to be used offline and they are often used by IT Admins and/or used on Servers.
Installation from an iso file don't require network connection most of the time. Activities deviating from these situations can be considered as highly suspicious. Below queries detects opening a mounted image, process creation under a mounted image, and network connection from a process created under a mounted image.
All detections can be used seperately or combined together to generate a higher fidelity alert. Detect opening of a mounted image:

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	No specific technique

Event coverage

Provider	Event/ActionType	Title
Sysmon	Event ID 11	FileCreate
Sysmon	Event ID 13	RegistryEvent (Value Set)
Security-Auditing	Event ID 4657	A registry value was modified.
Security-Auditing	Event ID 4663	An attempt was made to access an object.
Defender-DeviceFileEvents	any	File activity (any)
Defender-DeviceRegistryEvents	RegistryValueSet	Registry value set

Rule body kusto

// Author: Cyb3rMonk(https://twitter.com/Cyb3rMonk, https://mergene.medium.com)
// Link to original post:
// Part-1: https://mergene.medium.com/detecting-initial-access-html-smuggling-and-iso-images-part-1-c4f953edd13f?source=friends_link&sk=e685d7d44928edd142972a4041463f10
// Part-2: https://mergene.medium.com/detecting-initial-access-html-smuggling-and-iso-images-part-2-f8dd600430e2?source=friends_link&sk=38b7cd310a4929c25d3eefc545683d5f
//
//
// Query parameters:
let lookback = 1h;
// Get ISO mount events
DeviceFileEvents
| where Timestamp > ago(lookback)
| where FileName endswith ".iso.lnk" or FileName endswith ".img.lnk"
// Exclude servers and workstation used by IT admins if needed.

// Author: Cyb3rMonk(https://twitter.com/Cyb3rMonk, https://mergene.medium.com)
// Link to original post:
// Part-1: https://mergene.medium.com/detecting-initial-access-html-smuggling-and-iso-images-part-1-c4f953edd13f?source=friends_link&sk=e685d7d44928edd142972a4041463f10
// Part-2: https://mergene.medium.com/detecting-initial-access-html-smuggling-and-iso-images-part-2-f8dd600430e2?source=friends_link&sk=38b7cd310a4929c25d3eefc545683d5f
//
//
// Query parameters:
let lookback = 1h;
// Get mounted devices and extract the folder name
DeviceRegistryEvents
| where Timestamp > ago(lookback)
| where ActionType == "RegistryValueSet" and RegistryKey == @"HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices" and RegistryValueName startswith @"\DosDevices\"
| extend Folder = toupper(replace(@'\\DosDevices\\(\w:)',@'\1',RegistryValueName)) // Extract the folder name
// Get process creations that have the mounted image as the FolderPath
| join kind=inner 
    (
    DeviceProcessEvents
    | where Timestamp > ago(lookback)
    | extend Folder = toupper(replace(@'(\w:)\\.*',@'\1',FolderPath))
    ) on DeviceId, Folder
// If needed, exclude servers from the results.

// Author: Cyb3rMonk(https://twitter.com/Cyb3rMonk, https://mergene.medium.com)
// Link to original post:
// Part-1: https://mergene.medium.com/detecting-initial-access-html-smuggling-and-iso-images-part-1-c4f953edd13f?source=friends_link&sk=e685d7d44928edd142972a4041463f10
// Part-2: https://mergene.medium.com/detecting-initial-access-html-smuggling-and-iso-images-part-2-f8dd600430e2?source=friends_link&sk=38b7cd310a4929c25d3eefc545683d5f
//
//
// Query parameters:
let lookback = 1h;
// Get mounted devices and extract the folder name
DeviceRegistryEvents
| where Timestamp > ago(lookback)
| where ActionType == "RegistryValueSet" and RegistryKey == @"HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices" and RegistryValueName startswith @"\DosDevices\"
| extend Folder = toupper(replace(@'\\DosDevices\\(\w:)',@'\1',RegistryValueName)) // Extract the folder name
// Get network connections of processes that have the mounted image as the InitiatingProcessFolderPath
| join kind=inner 
    (
    DeviceNetworkEvents
    | where Timestamp > ago(lookback)
    | extend Folder = toupper(replace(@'(\w:)\\.*',@'\1',InitiatingProcessFolderPath))
    ) on DeviceId, Folder
// If needed, exclude the legitimate activity and servers

Stages and Predicates

Parameters

let lookback = 1h;

Stage 1: `source`

DeviceFileEvents

Stage 2: `where`

| where Timestamp > ago(lookback)

Stage 3: `where`

| where FileName endswith ".iso.lnk" or FileName endswith ".img.lnk"

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
`FileName`	ends_with	`.img.lnk` `.iso.lnk`

`j` / `k`	Scroll down / up
`d` / `u`	Half-page down / up
`gg` / `G`	Top / bottom
`h` / `l`	History back / forward
`f`	Follow link (`Shift` = new tab)
`/`	Focus search
`?`	Toggle this help
`↑` / `↓`	Navigate search results
`Enter`	Open highlighted result
`Esc`	Close results / dialog

`type:`	`events` / `rules` / `providers`
`vendor:`	`sigma` / `elastic` / `splunk` / `kusto` / `chronicle` (vendor name alone also works: `sigma:`, `kql:`, `secops:`…)
`tactic:`	TA-id, slug, or name: `credential_access`, `TA0006`
`technique:`	technique or sub-technique ID: `T1003`, `T1003.001` (alias `tech:`)
`severity:`	`critical` / `high` / `medium` / `low` / `informational` (alias `sev:`)
`risk_score`	Numeric comparison on the Elastic risk score (0 to 100): `risk_score>50`, `risk_score<=20`, `risk_score=99` (alias `risk`; Elastic rules only)
`stages:`	Rules with exactly N pipeline stages
`correlation:`	`single_event` / `sequence` / `alternatives` / `alternatives_cross_log` / `all_required` / `correlated`
`with:`	Co-occurrence event-id; stacks (`with:4624 with:4769`) to require all, while a comma list in one occurrence (`with:4624,4769`) is an either-or group. Implies multi-event
`like:`	Structural neighbors of a rule slug (equivalents + subsumption stricter / broader): `like:comsvcs_lsass_memory_dump-splunk-sysmon`
`groupby:`	Entity-grouping substring match against `group_by_keys`: `groupby:user`, `groupby:host`
`uses:`	Rules whose predicate tree touches the field (any kind, any value): `uses:CommandLine`
`excludes:`	Rules with top-level `not()` clauses on the field (FP whitelists): `excludes:ParentImage`
`field:` / `value:`	Predicate search; narrows rule cards to those with a matching leaf and drives the indicator tier. Unquoted = substring, wildcards allowed (`value:mimikatz`)
`indicator:`	Shorthand for `field:F value:V`: `indicator:Image=*\powershell.exe`
`kind:`	Filter by predicate kind. Narrows rule cards to those carrying a matching predicate leaf (`vendor:elastic kind:cidr_match`) and drives the indicator tier: `contains` / `starts_with` / `ends_with` / `regex` / `cidr` / `eq` / `in` … (operator aliases `op:`/`match:`)
`has:` / `no:`	`sample`, `field`, `notes`, `refs`, `trace`, `thirdparty`, `rule`, `pattern`, `timewindow`, `threshold`, `newterms`, `sigma`/`elastic`/`splunk`/`kusto`/`chronicle`
`-op:val`	Exclude matches; works on most operators but not `type:`/`like:`/`has:`/`no:` (use `no:<flag>` to exclude a rule flag): `tactic:execution -vendor:splunk`. Standalone `-kind:`/`-field:`/`-value:` drop every rule carrying a matching predicate leaf (`type:rules -kind:is_null`)
`field:"…"` / `value:"…"`	Quoted value = anchored exact match (also allows spaces): `value:"net user"`
`a,b`	Comma = OR inside one operator (`vendor:sigma,elastic`, `severity:high,critical`); repeating a facet merges the same way. `field:`/`value:` never split (literal commas)
`vendors:` / `stage:`	Singular and plural spellings fold to the canonical operator and value: `tactics:` = `tactic:`, `type:event` = `type:events`, `correlation:sequences` = `correlation:sequence`, `has:thresholds` = `has:threshold`
`"quoted phrase"`	Exact-match a multi-word phrase (free text)

Spearphishing Attachment: ISO Images (Microsoft Defender for Endpoint)

MITRE ATT&CK coverage

Event coverage

Rule body kusto

Stages and Predicates

Parameters

Stage 1: `source`

Stage 2: `where`

Stage 3: `where`

Indicators

Keyboard shortcuts

Search operators

Spearphishing Attachment: ISO Images (Microsoft Defender for Endpoint)

MITRE ATT&CK coverage

Event coverage

Rule body kusto

Stages and Predicates

Parameters

Stage 1: source

Stage 2: where

Stage 3: where

Indicators

Stage 1: `source`

Stage 2: `where`

Stage 3: `where`