Potential CVE-2021-42287 Exploitation Attempt

Status: test
Severity: medium
Log source: product windows, service system
Author: frack113
Source: github.com/SigmaHQ/sigma

The attacker creates a computer object using those permissions with a password known to her. After that she clears the attribute ServicePrincipalName on the computer object. Because she created the object (CREATOR OWNER), she gets granted additional permissions and can do many changes to the object.

MITRE ATT&CK coverage

Tactic	Techniques
Credential Access	`T1558.003` Steal or Forge Kerberos Tickets: Kerberoasting

Event coverage

Provider	Event	Title
Directory-Services-SAM	Event ID 16990	The security account manager blocked a non-administrator from creating an Active Directory account in this domain with mismatched objectClass and u...
Directory-Services-SAM	Event ID 16991	The security account manager blocked a non-administrator from creating or renaming a computer account using an invalid sAMAccountName.

Rule body yaml

title: Potential CVE-2021-42287 Exploitation Attempt
id: e80a0fee-1a62-4419-b31e-0d0db6e6013a
related:
    - id: 44bbff3e-4ca3-452d-a49a-6efa4cafa06f
      type: similar
status: test
description: |
    The attacker creates a computer object using those permissions with a password known to her.
    After that she clears the attribute ServicePrincipalName on the computer object.
    Because she created the object (CREATOR OWNER), she gets granted additional permissions and can do many changes to the object.
references:
    - https://cloudbrothers.info/en/exploit-kerberos-samaccountname-spoofing/
author: frack113
date: 2021-12-15
modified: 2023-04-14
tags:
    - attack.credential-access
    - attack.t1558.003
    - detection.emerging-threats
    - cve.2021-42287
logsource:
    product: windows
    service: system
detection:
    selection:
        Provider_Name: Microsoft-Windows-Directory-Services-SAM  # Active Directory
        EventID:
            - 16990 # Object class and UserAccountControl validation failure
            - 16991 # SAM Account Name validation failure
    condition: selection
falsepositives:
    - Unknown
level: medium

Stages and Predicates

Stage 0: `condition`

selection

Stage 1: `selection`

selection:
    Provider_Name: Microsoft-Windows-Directory-Services-SAM
    EventID:
        - 16990
        - 16991

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
`Provider_Name`	eq	`Microsoft-Windows-Directory-Services-SAM`

`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)

Potential CVE-2021-42287 Exploitation Attempt

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection`

Indicators

Keyboard shortcuts

Search operators

Potential CVE-2021-42287 Exploitation Attempt

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection

Indicators

Stage 0: `condition`

Stage 1: `selection`