Potential XCSSET Malware Infection

Status: test
Severity: medium
Log source: product macos, category process_creation
Author: Tim Rauch (rule), Elastic (idea)
Source: github.com/SigmaHQ/sigma

Identifies the execution traces of the XCSSET malware. XCSSET is a macOS trojan that primarily spreads via Xcode projects and maliciously modifies applications. Infected users are also vulnerable to having their credentials, accounts, and other vital data stolen.

MITRE ATT&CK coverage

Tactic	Techniques
Command & Control	No specific technique

Event coverage

Provider	Event	Title
ESF	exec	Process Execution (Notify)

Rule body yaml

title: Potential XCSSET Malware Infection
id: 47d65ac0-c06f-4ba2-a2e3-d263139d0f51
status: test
description: Identifies the execution traces of the XCSSET malware. XCSSET is a macOS trojan that primarily spreads via Xcode projects and maliciously modifies applications. Infected users are also vulnerable to having their credentials, accounts, and other vital data stolen.
references:
    - https://github.com/elastic/protections-artifacts/commit/746086721fd385d9f5c6647cada1788db4aea95f#diff-f5deb07688e1a8dec9530bc3071967b2da5c16b482e671812b864c37beb28f08
    - https://malpedia.caad.fkie.fraunhofer.de/details/osx.xcsset
author: Tim Rauch (rule), Elastic (idea)
date: 2022-10-17
tags:
    - attack.command-and-control
logsource:
    category: process_creation
    product: macos
detection:
    selection_1_curl:
        ParentImage|endswith: '/bash'
        Image|endswith: '/curl'
        CommandLine|contains:
            - '/sys/log.php'
            - '/sys/prepod.php'
            - '/sys/bin/Pods'
    selection_1_https:
        CommandLine|contains: 'https://'
    selection_other_1:
        ParentImage|endswith: '/bash'
        Image|endswith: '/osacompile'
        CommandLine|contains|all:
            - '/Users/'
            - '/Library/Group Containers/'
    selection_other_2:
        ParentImage|endswith: '/bash'
        Image|endswith: '/plutil'
        CommandLine|contains|all:
            - 'LSUIElement'
            - '/Users/'
            - '/Library/Group Containers/'
    selection_other_3:
        Image|endswith: '/zip'
        CommandLine|contains|all:
            - '-r'
            - '/Users/'
            - '/Library/Group Containers/'
    condition: all of selection_1_* or 1 of selection_other_*
falsepositives:
    - Unknown
level: medium

Stages and Predicates

Stage 0: `condition`

all of selection_1_* or 1 of selection_other_*

Stage 1: `selection_1_curl`

selection_1_curl:
    ParentImage|endswith: '/bash'
    Image|endswith: '/curl'
    CommandLine|contains:
        - '/sys/log.php'
        - '/sys/prepod.php'
        - '/sys/bin/Pods'

Stage 2: `selection_1_https`

selection_1_https:
    CommandLine|contains: 'https://'

Stage 3: `selection_other_1`

selection_other_1:
    ParentImage|endswith: '/bash'
    Image|endswith: '/osacompile'
    CommandLine|contains|all:
        - '/Users/'
        - '/Library/Group Containers/'

Stage 4: `selection_other_2`

selection_other_2:
    ParentImage|endswith: '/bash'
    Image|endswith: '/plutil'
    CommandLine|contains|all:
        - 'LSUIElement'
        - '/Users/'
        - '/Library/Group Containers/'

Stage 5: `selection_other_3`

selection_other_3:
    Image|endswith: '/zip'
    CommandLine|contains|all:
        - '-r'
        - '/Users/'
        - '/Library/Group Containers/'

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
`CommandLine`	match	`-r` `/Library/Group Containers/` `/Users/` `/sys/bin/Pods` `/sys/log.php` `/sys/prepod.php` `LSUIElement` `https://`
`Image`	ends_with	`/curl` `/osacompile` `/plutil` `/zip`
`ParentImage`	ends_with	`/bash`

`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 XCSSET Malware Infection

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_1_curl`

Stage 2: `selection_1_https`

Stage 3: `selection_other_1`

Stage 4: `selection_other_2`

Stage 5: `selection_other_3`

Indicators

Keyboard shortcuts

Search operators

Potential XCSSET Malware Infection

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_1_curl

Stage 2: selection_1_https

Stage 3: selection_other_1

Stage 4: selection_other_2

Stage 5: selection_other_3

Indicators

Stage 0: `condition`

Stage 1: `selection_1_curl`

Stage 2: `selection_1_https`

Stage 3: `selection_other_1`

Stage 4: `selection_other_2`

Stage 5: `selection_other_3`