Potential Persistence Via Outlook Today Page

Status: test
Severity: high
Log source: product windows, category registry_set
Author: Tobias Michalski (Nextron Systems), David Bertho (@dbertho) & Eirik Sveen (@0xSV1), Storebrand
Source: github.com/SigmaHQ/sigma

Detects potential persistence activity via outlook today page. An attacker can set a custom page to execute arbitrary code and link to it via the registry values "URL" and "UserDefinedUrl".

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1112` Modify Registry
Defense Impairment	`T1112` Modify Registry

Event coverage

Provider	Event	Title
Sysmon	Event ID 13	RegistryEvent (Value Set)

Rule body yaml

title: Potential Persistence Via Outlook Today Page
id: 487bb375-12ef-41f6-baae-c6a1572b4dd1
related:
    - id: ddd171b5-2cc6-4975-9e78-f0eccd08cc76
      type: similar
status: test
description: |
    Detects potential persistence activity via outlook today page.
    An attacker can set a custom page to execute arbitrary code and link to it via the registry values "URL" and "UserDefinedUrl".
references:
    - https://speakerdeck.com/heirhabarov/hunting-for-persistence-via-microsoft-exchange-server-or-outlook?slide=74
    - https://trustedsec.com/blog/specula-turning-outlook-into-a-c2-with-one-registry-change
author: Tobias Michalski (Nextron Systems), David Bertho (@dbertho) & Eirik Sveen (@0xSV1), Storebrand
date: 2021-06-10
modified: 2024-08-07
tags:
    - attack.persistence
    - attack.defense-impairment
    - attack.t1112
logsource:
    product: windows
    category: registry_set
detection:
    selection_main:
        TargetObject|contains|all:
            - 'Software\Microsoft\Office\'
            - '\Outlook\Today\'
    selection_value_stamp:
        TargetObject|endswith: '\Stamp'
        Details: 'DWORD (0x00000001)'
    selection_value_url:
        TargetObject|endswith:
            - '\URL'
            - '\UserDefinedUrl'
    filter_main_office:
        Image|startswith:
            - 'C:\Program Files\Common Files\Microsoft Shared\ClickToRun\'
            - 'C:\Program Files\Common Files\Microsoft Shared\ClickToRun\Updates\'
        Image|endswith: '\OfficeClickToRun.exe'
    condition: selection_main and 1 of selection_value_* and not 1 of filter_main_*
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: `condition`

selection_main and 1 of selection_value_* and not 1 of filter_main_*

Stage 1: `selection_main`

selection_main:
    TargetObject|contains|all:
        - 'Software\Microsoft\Office\'
        - '\Outlook\Today\'

Stage 2: `selection_value_stamp`

selection_value_stamp:
    TargetObject|endswith: '\Stamp'
    Details: 'DWORD (0x00000001)'

Stage 3: `selection_value_url`

selection_value_url:
    TargetObject|endswith:
        - '\URL'
        - '\UserDefinedUrl'

Stage 4: `not filter_main_office`

filter_main_office:
    Image|startswith:
        - 'C:\Program Files\Common Files\Microsoft Shared\ClickToRun\'
        - 'C:\Program Files\Common Files\Microsoft Shared\ClickToRun\Updates\'
    Image|endswith: '\OfficeClickToRun.exe'

Exclusions

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

Field	Kind	Excluded values
`Image`	starts_with	`C:\Program Files\Common Files\Microsoft Shared\ClickToRun\`
`Image`	starts_with	`C:\Program Files\Common Files\Microsoft Shared\ClickToRun\Updates\`
`Image`	ends_with	`\OfficeClickToRun.exe`

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
`Details`	eq	`DWORD (0x00000001)` corpus 40 (sigma 36, chronicle 4)
`TargetObject`	ends_with	`\Stamp` `\URL` corpus 2 (sigma 2) `\UserDefinedUrl`
`TargetObject`	match	`Software\Microsoft\Office\` corpus 2 (sigma 2) `\Outlook\Today\`

`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 Persistence Via Outlook Today Page

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_main`

Stage 2: `selection_value_stamp`

Stage 3: `selection_value_url`

Stage 4: `not filter_main_office`

Exclusions

Indicators

Keyboard shortcuts

Search operators

Potential Persistence Via Outlook Today Page

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_main

Stage 2: selection_value_stamp

Stage 3: selection_value_url

Stage 4: not filter_main_office

Exclusions

Indicators

Stage 0: `condition`

Stage 1: `selection_main`

Stage 2: `selection_value_stamp`

Stage 3: `selection_value_url`

Stage 4: `not filter_main_office`