NetSYnc attack

Status: experimental
Severity: high
Log source: product windows, service security
Author: mdecrevoisier
Source: github.com/mdecrevoisier/SIGMA-detection-rules

NetSync allows an attacker to take the NTLM hash of a Domain Controller (DC) machine account ("usually" identified by ending in "$") and using it to obtain the NTLM machine account hash of another machine account through impersonation (similar to, but different from, DCSync). Where DCSync can obtain user account passwords, NetSync is limited to machine accounts. The other main differentiator between DCSync and NetSync is that DCSync will make use of Microsoft's Directory Replication Service (DRS) Remote Protocol, whereas NetSync uses the older Netlogon Remote Protocol (MS-NRPC)

MITRE ATT&CK coverage

Tactic	Techniques
Credential Access	`T1003.006` OS Credential Dumping: DCSync

Event coverage

Provider	Event	Title
Security-Auditing	Event ID 4624	An account was successfully logged on.
Security-Auditing	Event ID 5145	A network share object was checked to see whether client can be granted desired access.

Rule body yaml

title: NetSYnc attack
description: NetSync allows an attacker to take the NTLM hash of a Domain Controller (DC) machine account ("usually" identified by ending in "$") and using it to obtain the NTLM machine account hash of another machine account through impersonation (similar to, but different from, DCSync). Where DCSync can obtain user account passwords, NetSync is limited to machine accounts. The other main differentiator between DCSync and NetSync is that DCSync will make use of Microsoft's Directory Replication Service (DRS) Remote Protocol, whereas NetSync uses the older Netlogon Remote Protocol (MS-NRPC)
correlation: ID 5145 SubjectLogonId 0x1f4a6c852 AND ID 4624 TargetLogonId 0x1f4a6c852
references:
- https://github.com/Neo23x0/sigma/blob/c56cd2dfff6343f3694ef4fd606a305415599737/rules-unsupported/win_dumping_ntdsdit_via_netsync.yml
- https://fr.slideshare.net/heirhabarov/hunting-for-credentials-dumping-in-windows-environment
- https://www.trustedsec.com/blog/the-tale-of-the-lost-but-not-forgotten-undocumented-netsync-part-1/
- https://www.trustedsec.com/blog/the-tale-of-the-lost-but-not-forgotten-undocumented-netsync-part-2/
tags:
- attack.credential_access
- attack.t1003.006
author: mdecrevoisier
status: experimental
logsource:
  product: windows
  service: security
detection: #  lsadump::netsync /dc:<dc_fqdn> /user:dc1$ /ntlm:<ntlmhash> /account:srv02$

  selection_login:
    EventID: 4624
    Computer: '%domain_controllers%'
    TargetUserSid: S-1-5-21-
    LogonType: 3
    AuthenticationPackageName: Kerberos

  selection_share:
    EventID: 5145
    Computer: '%domain_controllers%'
    ShareName: \\*\IPC$
    RelativeTargetName: NETLOGON

  filter:
    - SubjectUserName|endswith: $
    - SubjectUserSid: S-1-5-7 #  ANONYMOUS LOGON
    - IpAddress:
      - '%domain_controllers%'
      - '%exchange_servers%'

  condition: selection_login and selection_share and not filter
falsepositives:
- Exchange servers
level: high

Stages and Predicates

Stage 0: `condition`

selection_login and selection_share and not filter

Stage 1: `selection_login`

selection_login:
  EventID: 4624
  Computer: '%domain_controllers%'
  TargetUserSid: S-1-5-21-
  LogonType: 3
  AuthenticationPackageName: Kerberos

Stage 2: `selection_share`

selection_share:
  EventID: 5145
  Computer: '%domain_controllers%'
  ShareName: \\*\IPC$
  RelativeTargetName: NETLOGON

Stage 3: `not filter`

filter:
  - SubjectUserName|endswith: $
  - SubjectUserSid: S-1-5-7
  - IpAddress:
    - '%domain_controllers%'
    - '%exchange_servers%'

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

Field	Kind	Excluded values
`IpAddress`	eq	`%domain_controllers%`
`IpAddress`	eq	`%exchange_servers%`
`SubjectUserName`	ends_with	`$`
`SubjectUserSid`	eq	`S-1-5-7`

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
`AuthenticationPackageName`	eq	`Kerberos` corpus 5 (sigma 2, elastic 2, splunk 1)
`Computer`	eq	`%domain_controllers%` corpus 3 (sigma 3)
`LogonType`	eq	`3` corpus 40 (splunk 13, sigma 12, elastic 9, kusto 6)
`RelativeTargetName`	eq	`NETLOGON`
`ShareName`	wildcard	`\\*\IPC$` corpus 11 (sigma 11)
`TargetUserSid`	eq	`S-1-5-21-`

`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)

NetSYnc attack

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_login`

Stage 2: `selection_share`

Stage 3: `not filter`

Exclusions

Indicators

Keyboard shortcuts

Search operators

NetSYnc attack

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_login

Stage 2: selection_share

Stage 3: not filter

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection_login`

Stage 2: `selection_share`

Stage 3: `not filter`