Potential Homoglyph Attack Using Lookalike Characters in Filename

Status: test
Severity: medium
Log source: product windows, category file_event
Author: Micah Babinski, @micahbabinski
Source: github.com/SigmaHQ/sigma

Detects the presence of unicode characters which are homoglyphs, or identical in appearance, to ASCII letter characters. This is used as an obfuscation and masquerading techniques. Only "perfect" homoglyphs are included; these are characters that are indistinguishable from ASCII characters and thus may make excellent candidates for homoglyph attack characters.

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1036.003` Masquerading: Rename Legitimate Utilities

Event coverage

Provider	Event	Title
Sysmon	Event ID 11	FileCreate

Rule body yaml

title: Potential Homoglyph Attack Using Lookalike Characters in Filename
id: 4f1707b1-b50b-45b4-b5a2-3978b5a5d0d6
status: test
description: |
    Detects the presence of unicode characters which are homoglyphs, or identical in appearance, to ASCII letter characters.
    This is used as an obfuscation and masquerading techniques. Only "perfect" homoglyphs are included; these are characters that
    are indistinguishable from ASCII characters and thus may make excellent candidates for homoglyph attack characters.
references:
    - https://redcanary.com/threat-detection-report/threats/socgholish/#threat-socgholish
    - http://www.irongeek.com/homoglyph-attack-generator.php
author: Micah Babinski, @micahbabinski
date: 2023-05-08
tags:
    - attack.stealth
    - attack.t1036
    - attack.t1036.003
logsource:
    category: file_event
    product: windows
detection:
    selection_upper:
        TargetFilename|contains:
            - "\u0410" # А/A
            - "\u0412" # В/B
            - "\u0415" # Е/E
            - "\u041a" # К/K
            - "\u041c" # М/M
            - "\u041d" # Н/H
            - "\u041e" # О/O
            - "\u0420" # Р/P
            - "\u0421" # С/C
            - "\u0422" # Т/T
            - "\u0425" # Х/X
            - "\u0405" # Ѕ/S
            - "\u0406" # І/I
            - "\u0408" # Ј/J
            - "\u04ae" # Ү/Y
            - "\u04c0" # Ӏ/I
            - "\u050C" # Ԍ/G
            - "\u051a" # Ԛ/Q
            - "\u051c" # Ԝ/W
            - "\u0391" # Α/A
            - "\u0392" # Β/B
            - "\u0395" # Ε/E
            - "\u0396" # Ζ/Z
            - "\u0397" # Η/H
            - "\u0399" # Ι/I
            - "\u039a" # Κ/K
            - "\u039c" # Μ/M
            - "\u039d" # Ν/N
            - "\u039f" # Ο/O
            - "\u03a1" # Ρ/P
            - "\u03a4" # Τ/T
            - "\u03a5" # Υ/Y
            - "\u03a7" # Χ/X
    selection_lower:
        TargetFilename|contains:
            - "\u0430" # а/a
            - "\u0435" # е/e
            - "\u043e" # о/o
            - "\u0440" # р/p
            - "\u0441" # с/c
            - "\u0445" # х/x
            - "\u0455" # ѕ/s
            - "\u0456" # і/i
            - "\u04cf" # ӏ/l
            - "\u0458" # ј/j
            - "\u04bb" # һ/h
            - "\u0501" # ԁ/d
            - "\u051b" # ԛ/q
            - "\u051d" # ԝ/w
            - "\u03bf" # ο/o
    condition: 1 of selection_*
falsepositives:
    - File names with legitimate Cyrillic text. Will likely require tuning (or not be usable) in countries where these alphabets are in use.
level: medium

Stages and Predicates

Stage 0: `condition`

1 of selection_*

Stage 1: `selection_upper`

selection_upper:
    TargetFilename|contains:
        - "\u0410"
        - "\u0412"
        - "\u0415"
        - "\u041a"
        - "\u041c"
        - "\u041d"
        - "\u041e"
        - "\u0420"
        - "\u0421"
        - "\u0422"
        - "\u0425"
        - "\u0405"
        - "\u0406"
        - "\u0408"
        - "\u04ae"
        - "\u04c0"
        - "\u050C"
        - "\u051a"
        - "\u051c"
        - "\u0391"
        - "\u0392"
        - "\u0395"
        - "\u0396"
        - "\u0397"
        - "\u0399"
        - "\u039a"
        - "\u039c"
        - "\u039d"
        - "\u039f"
        - "\u03a1"
        - "\u03a4"
        - "\u03a5"
        - "\u03a7"

Stage 2: `selection_lower`

selection_lower:
    TargetFilename|contains:
        - "\u0430"
        - "\u0435"
        - "\u043e"
        - "\u0440"
        - "\u0441"
        - "\u0445"
        - "\u0455"
        - "\u0456"
        - "\u04cf"
        - "\u0458"
        - "\u04bb"
        - "\u0501"
        - "\u051b"
        - "\u051d"
        - "\u03bf"

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
`TargetFilename`	match	`Α` `Β` `Ε` `Ζ` `Η` `Ι` `Κ` `Μ` `Ν` `Ο` `Ρ` `Τ` `Υ` `Χ` `ο` `Ѕ` `І` `Ј` `А` `В` `Е` `К` `М` `Н` `О` `Р` `С` `Т` `Х` `а` `е` `о` `р` `с` `х` `ѕ` `і` `ј` `Ү` `һ` `Ӏ` `ӏ` `ԁ` `Ԍ` `Ԛ` `ԛ` `Ԝ` `ԝ`

`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 Homoglyph Attack Using Lookalike Characters in Filename

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_upper`

Stage 2: `selection_lower`

Indicators

Keyboard shortcuts

Search operators

Potential Homoglyph Attack Using Lookalike Characters in Filename

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_upper

Stage 2: selection_lower

Indicators

Stage 0: `condition`

Stage 1: `selection_upper`

Stage 2: `selection_lower`