Suspicious SPN logon from workstation (DumpGuard)

Author: Robbe Van den Daele
Source: github.com/HybridBrothers/Hunting-Queries-Detection-Rules

With the DumpGuard tool, attackers are able to dump credetials via Remote Credential Guard on devices that have Credential Guard enabled. Since the DumpGuard tool needs to use an SPN enabled account (in the POC they use a machine account) for two exploitation scenario's, it is interesting to look for TGT requests happening from client devices for SPN enabled accounts.

MITRE ATT&CK coverage

Tactic	Techniques
Credential Access	`T1003.004` OS Credential Dumping: LSA Secrets

References

Rule body yaml

let spn_accounts = toscalar(
    // Search for all SPNs we can find in historic logs
    IdentityLogonEvents
    | where TimeGenerated > ago(14d)
    | where Application == "Active Directory"
    | where isnotempty(AdditionalFields.Spns)
    | extend Spns = split(AdditionalFields.Spns, ",")
    | summarize make_set(Spns)
);
let workstation_subnets = toscalar(
    DeviceNetworkInfo
    | where TimeGenerated > ago(14d)
    // Filter out empty device names
    | where isnotempty(DeviceName)
    // Expand IP Addresses
    | mv-expand todynamic(IPAddresses)
    // Focus on device name and IP Address info
    | distinct DeviceName, tostring(IPAddresses)
    // Filter out IPv6 addresses, /32 addresses, and APIPA addresses
    | where todynamic(IPAddresses).IPAddress !contains ":"
    | where todynamic(IPAddresses).SubnetPrefix != "32"
    | where todynamic(IPAddresses).IPAddress !startswith "169.254"
    // Find Device Type of the device
    | join kind=inner (
        DeviceInfo
        | where TimeGenerated > ago(30d)
        | distinct DeviceName, DeviceType
    ) on DeviceName
    // Only focus on workstations
    | where DeviceType == "Workstation"
    // Create Network Address based on the host IP Address and create a distinct list
    | extend NetworkAddress = format_ipv4_mask(tostring(todynamic(IPAddresses).IPAddress), tolong(todynamic(IPAddresses).SubnetPrefix))
    | summarize make_set(NetworkAddress)
);
IdentityLogonEvents
| where TimeGenerated > ago(1h)
// Get AD TGT requests by looking for Kerberos requests to KRBTGT account
| where Application == "Active Directory"
| where Protocol == "Kerberos"
| where AdditionalFields.Spns contains "krbtgt"
// Check for requests to account names with SPNs
| where AccountName in (spn_accounts)
// Check if IP Address is from a client range
| where ipv4_is_in_any_range(IPAddress, workstation_subnets)
// Optional - Ignore failed logins
| where ActionType != "LogonFailed"

Stages and Predicates

Let binding: `spn_accounts`

let spn_accounts = toscalar(
    IdentityLogonEvents
    | where TimeGenerated > ago(14d)
    | where Application == "Active Directory"
    | where isnotempty(AdditionalFields.Spns)
    | extend Spns = split(AdditionalFields.Spns, ",")
    | summarize make_set(Spns)
);

Let binding: `workstation_subnets`

let workstation_subnets = toscalar(
    DeviceNetworkInfo
    | where TimeGenerated > ago(14d)
    | where isnotempty(DeviceName)
    | mv-expand todynamic(IPAddresses)
    | distinct DeviceName, tostring(IPAddresses)
    | where todynamic(IPAddresses).IPAddress !contains ":"
    | where todynamic(IPAddresses).SubnetPrefix != "32"
    | where todynamic(IPAddresses).IPAddress !startswith "169.254"
    | join kind=inner (
        DeviceInfo
        | where TimeGenerated > ago(30d)
        | distinct DeviceName, DeviceType
    ) on DeviceName
    | where DeviceType == "Workstation"
    | extend NetworkAddress = format_ipv4_mask(tostring(todynamic(IPAddresses).IPAddress), tolong(todynamic(IPAddresses).SubnetPrefix))
    | summarize make_set(NetworkAddress)
);

Stage 1: `source`

IdentityLogonEvents

Stage 2: `where`

| where TimeGenerated > ago(1h)

Stage 3: `where`

| where Application == "Active Directory"

Stage 4: `where`

| where Protocol == "Kerberos"

Stage 5: `where`

| where AdditionalFields.Spns contains "krbtgt"

Stage 6: `where`

| where AccountName in (spn_accounts)

References spn_accounts (defined above).

Stage 7: `where`

| where ipv4_is_in_any_range(IPAddress, workstation_subnets)

References workstation_subnets (defined above).

Stage 8: `where`

| where ActionType != "LogonFailed"

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
`AccountName`	in	`spn_accounts` transforms: `cased`
`ActionType`	ne	`LogonFailed` transforms: `cased`
`Application`	eq	`Active Directory` transforms: `cased`
`Protocol`	eq	`Kerberos` transforms: `cased`
`Spns`	contains	`krbtgt`

`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)

Suspicious SPN logon from workstation (DumpGuard)

MITRE ATT&CK coverage

References

Rule body yaml

Stages and Predicates

Let binding: `spn_accounts`

Let binding: `workstation_subnets`

Stage 1: `source`

Stage 2: `where`

Stage 3: `where`

Stage 4: `where`

Stage 5: `where`

Stage 6: `where`

Stage 7: `where`

Stage 8: `where`

Indicators

Keyboard shortcuts

Search operators

Suspicious SPN logon from workstation (DumpGuard)

MITRE ATT&CK coverage

References

Rule body yaml

Stages and Predicates

Let binding: spn_accounts

Let binding: workstation_subnets

Stage 1: source

Stage 2: where

Stage 3: where

Stage 4: where

Stage 5: where

Stage 6: where

Stage 7: where

Stage 8: where

Indicators

Let binding: `spn_accounts`

Let binding: `workstation_subnets`

Stage 1: `source`

Stage 2: `where`

Stage 3: `where`

Stage 4: `where`

Stage 5: `where`

Stage 6: `where`

Stage 7: `where`

Stage 8: `where`