Detect Suspicious ncrypt.dll usage by process requesting Entra ID Nonce

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

This detection rule uses a WDAC audit policy to ingest missing DeviceImageLoad events in MDE, and check for suspicious processes using the ncrypt.dll and requesting an Entra ID Nonce. More information on the attack scenario this is detection is applicable for can be found in the references.

MITRE ATT&CK coverage

Tactic	Techniques
Credential Access	`T1555.004` Credentials from Password Stores: Windows Credential Manager, `T1606` Forge Web Credentials

References

Event coverage

Provider	ActionType	Title
Defender-DeviceEvents	any	Defender event (any)

Rule body yaml

let cli_tools = dynamic(["powershell", "python"]);
// Get all possible nonce requests
let nonce_requests = (
    DeviceNetworkEvents
    | where Timestamp > ago(1h)
    | where ActionType startswith "ConnectionSuccess"
    | where RemoteUrl =~ "login.microsoftonline.com"
    | project-rename NonceTimestamp = Timestamp
);
// Get suspicious ncrypt.dll usage via WDAC audit policy
DeviceEvents
| where Timestamp > ago(1h)
| where ActionType startswith "AppControl" and FileName =~ "ncrypt.dll"
// Check if the same initiating process is doing a nonce request
| join kind=inner nonce_requests on InitiatingProcessId, DeviceId
// Only flag when nonce was request 10min before of after ncrypt usage
| where Timestamp between (todatetime(NonceTimestamp - 10m) .. todatetime(NonceTimestamp + 10m))
| invoke FileProfile(InitiatingProcessSHA1, 1000)
| where (
    // Flag CLI tools
    InitiatingProcessFileName has_any (cli_tools) or 
    // Flag unknown processes
    GlobalPrevalence < 250
)

let cli_tools = dynamic(["powershell", "python"]);
// Get all possible nonce requests
let nonce_requests = (
    DeviceNetworkEvents
    | where TimeGenerated > ago(1h)
    | where ActionType startswith "ConnectionSuccess"
    | where RemoteUrl =~ "login.microsoftonline.com"
    | project-rename NonceTimestamp = TimeGenerated
);
// Get suspicious ncrypt.dll usage via WDAC audit policy
DeviceEvents
| where TimeGenerated > ago(1h)
| where ActionType startswith "AppControl" and FileName =~ "ncrypt.dll"
// Check if the same initiating process is doing a nonce request
| join kind=inner nonce_requests on InitiatingProcessId, DeviceId
// Only flag when nonce was request 10min before of after ncrypt usage
| where TimeGenerated between (todatetime(NonceTimestamp - 10m) .. todatetime(NonceTimestamp + 10m))
| invoke FileProfile(InitiatingProcessSHA1, 1000)
| where (
    // Flag CLI tools
    InitiatingProcessFileName has_any (cli_tools) or 
    // Flag unknown processes
    GlobalPrevalence < 250
)

Stages and Predicates

Parameters

let cli_tools = dynamic(["powershell", "python"]);

Let binding: `nonce_requests`

let nonce_requests = (
    DeviceNetworkEvents
    | where Timestamp > ago(1h)
    | where ActionType startswith "ConnectionSuccess"
    | where RemoteUrl =~ "login.microsoftonline.com"
    | project-rename NonceTimestamp = Timestamp
);

Stage 1: `source`

DeviceEvents

Stage 2: `where`

| where Timestamp > ago(1h)

Stage 3: `where`

| where ActionType startswith "AppControl" and FileName =~ "ncrypt.dll"

Stage 4: `join`

| join kind=inner nonce_requests on InitiatingProcessId, DeviceId

Stage 5: `where`

| where Timestamp between (todatetime(NonceTimestamp - 10m) .. todatetime(NonceTimestamp + 10m))

Stage 6: `invoke`

| invoke FileProfile(InitiatingProcessSHA1, 1000)

Stage 7: `where`

| where (
    InitiatingProcessFileName has_any (cli_tools) or 
    GlobalPrevalence < 250
)

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
`ActionType`	starts_with	`AppControl` corpus 5 (kusto 5) `ConnectionSuccess`
`FileName`	eq	`ncrypt.dll` corpus 4 (kusto 4)
`GlobalPrevalence`	lt	`250` transforms: `cased` corpus 4 (kusto 4)
`InitiatingProcessFileName`	match	`powershell` corpus 2 (kusto 2) `python` corpus 2 (kusto 2)
`RemoteUrl`	eq	`login.microsoftonline.com` corpus 3 (kusto 3)

`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)

Detect Suspicious ncrypt.dll usage by process requesting Entra ID Nonce

MITRE ATT&CK coverage

References

Event coverage

Rule body yaml

Stages and Predicates

Parameters

Let binding: `nonce_requests`

Stage 1: `source`

Stage 2: `where`

Stage 3: `where`

Stage 4: `join`

Stage 5: `where`

Stage 6: `invoke`

Stage 7: `where`

Indicators

Keyboard shortcuts

Search operators

Detect Suspicious ncrypt.dll usage by process requesting Entra ID Nonce

MITRE ATT&CK coverage

References

Event coverage

Rule body yaml

Stages and Predicates

Parameters

Let binding: nonce_requests

Stage 1: source

Stage 2: where

Stage 3: where

Stage 4: join

Stage 5: where

Stage 6: invoke

Stage 7: where

Indicators

Let binding: `nonce_requests`

Stage 1: `source`

Stage 2: `where`

Stage 3: `where`

Stage 4: `join`

Stage 5: `where`

Stage 6: `invoke`

Stage 7: `where`