Weak Encryption Enabled and Kerberoast

Status: test
Severity: high
Log source: product windows, service security
Author: @neu5ron
Source: github.com/SigmaHQ/sigma

Detects scenario where weak encryption is enabled for a user profile which could be used for hash/password cracking.

MITRE ATT&CK coverage

Tactic	Techniques
Defense Impairment	`T1685` Disable or Modify Tools

Event coverage

Provider	Event	Title
Security-Auditing	Event ID 4738	A user account was changed.

Rule body yaml

title: Weak Encryption Enabled and Kerberoast
id: f6de9536-0441-4b3f-a646-f4e00f300ffd
status: test
description: Detects scenario where weak encryption is enabled for a user profile which could be used for hash/password cracking.
references:
    - https://adsecurity.org/?p=2053
    - https://blog.harmj0y.net/redteaming/another-word-on-delegation/
author: '@neu5ron'
date: 2017-07-30
modified: 2021-11-27
tags:
    - attack.defense-impairment
    - attack.t1685
logsource:
    product: windows
    service: security
    definition: 'Requirements: Audit Policy : Account Management > Audit User Account Management, Group Policy : Computer Configuration\Windows Settings\Security Settings\Advanced Audit Policy Configuration\Audit Policies\Account Management\Audit User Account Management'
detection:
    selection:
        EventID: 4738
    # According to Microsoft, the bit values are listed here: https://learn.microsoft.com/en-us/previous-versions/windows/it-pro/windows-10/security/threat-protection/auditing/event-4720
    # However, that seems to be a simple copy from https://learn.microsoft.com/en-us/troubleshoot/windows-server/active-directory/useraccountcontrol-manipulate-account-properties
    # and the actual flags that are used are quite different and, unfortunately, not documented.
    # https://github.com/mdecrevoisier/EVTX-to-MITRE-Attack/ contains a number of EVTX files with relevant events, which can be used to extract
    # the following values.
    olduac_des: # 0x8000
        OldUacValue|endswith:
            - 8???
            - 9???
            - A???
            - B???
            - C???
            - D???
            - E???
            - F???
    newuac_des:
        NewUacValue|endswith:
            - 8???
            - 9???
            - A???
            - B???
            - C???
            - D???
            - E???
            - F???
    olduac_preauth: # 0x10000
        OldUacValue|endswith:
            - 1????
            - 3????
            - 5????
            - 7????
            - 9????
            - B????
            - D????
            - F????
    newuac_preauth:
        NewUacValue|endswith:
            - 1????
            - 3????
            - 5????
            - 7????
            - 9????
            - B????
            - D????
            - F????
    olduac_encrypted: # 0x800
        OldUacValue|endswith:
            - 8??
            - 9??
            - A??
            - B??
            - C??
            - D??
            - E??
            - F??
    newuac_encrypted:
        NewUacValue|endswith:
            - 8??
            - 9??
            - A??
            - B??
            - C??
            - D??
            - E??
            - F??
    condition: selection and ((newuac_des and not olduac_des) or (newuac_preauth and not olduac_preauth) or (newuac_encrypted and not olduac_encrypted))
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: `condition`

selection and ((newuac_des and not olduac_des) or (newuac_preauth and not olduac_preauth) or (newuac_encrypted and not olduac_encrypted))

Stage 1: `selection`

selection:
    EventID: 4738

Stage 2: `newuac_des`

newuac_des:
    NewUacValue|endswith:
        - 8???
        - 9???
        - A???
        - B???
        - C???
        - D???
        - E???
        - F???

Stage 3: `not olduac_des`

olduac_des:
    OldUacValue|endswith:
        - 8???
        - 9???
        - A???
        - B???
        - C???
        - D???
        - E???
        - F???

Stage 4: `newuac_preauth`

newuac_preauth:
    NewUacValue|endswith:
        - 1????
        - 3????
        - 5????
        - 7????
        - 9????
        - B????
        - D????
        - F????

Stage 5: `not olduac_preauth`

olduac_preauth:
    OldUacValue|endswith:
        - 1????
        - 3????
        - 5????
        - 7????
        - 9????
        - B????
        - D????
        - F????

Stage 6: `newuac_encrypted`

newuac_encrypted:
    NewUacValue|endswith:
        - 8??
        - 9??
        - A??
        - B??
        - C??
        - D??
        - E??
        - F??

Stage 7: `not olduac_encrypted`

olduac_encrypted:
    OldUacValue|endswith:
        - 8??
        - 9??
        - A??
        - B??
        - C??
        - D??
        - E??
        - F??

Exclusions

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

Field	Kind	Excluded values
`OldUacValue`	ends_with	`8???`
`OldUacValue`	ends_with	`9???`
`OldUacValue`	ends_with	`A???`
`OldUacValue`	ends_with	`B???`
`OldUacValue`	ends_with	`C???`
`OldUacValue`	ends_with	`D???`
`OldUacValue`	ends_with	`E???`
`OldUacValue`	ends_with	`F???`
`OldUacValue`	ends_with	`1????`
`OldUacValue`	ends_with	`3????`
`OldUacValue`	ends_with	`5????`
`OldUacValue`	ends_with	`7????`
`OldUacValue`	ends_with	`9????`
`OldUacValue`	ends_with	`B????`
`OldUacValue`	ends_with	`D????`
`OldUacValue`	ends_with	`F????`
`OldUacValue`	ends_with	`8??`
`OldUacValue`	ends_with	`9??`
`OldUacValue`	ends_with	`A??`
`OldUacValue`	ends_with	`B??`
`OldUacValue`	ends_with	`C??`
`OldUacValue`	ends_with	`D??`
`OldUacValue`	ends_with	`E??`
`OldUacValue`	ends_with	`F??`

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
`NewUacValue`	ends_with	`1????` `3????` `5????` `7????` `8??` `8???` `9??` `9???` `9????` `A??` `A???` `B??` `B???` `B????` `C??` `C???` `D??` `D???` `D????` `E??` `E???` `F??` `F???` `F????`

`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)

Weak Encryption Enabled and Kerberoast

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `newuac_des`

Stage 3: `not olduac_des`

Stage 4: `newuac_preauth`

Stage 5: `not olduac_preauth`

Stage 6: `newuac_encrypted`

Stage 7: `not olduac_encrypted`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Weak Encryption Enabled and Kerberoast

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection

Stage 2: newuac_des

Stage 3: not olduac_des

Stage 4: newuac_preauth

Stage 5: not olduac_preauth

Stage 6: newuac_encrypted

Stage 7: not olduac_encrypted

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection`

Stage 2: `newuac_des`

Stage 3: `not olduac_des`

Stage 4: `newuac_preauth`

Stage 5: `not olduac_preauth`

Stage 6: `newuac_encrypted`

Stage 7: `not olduac_encrypted`