Webshell Tool Reconnaissance Activity

Status: test
Severity: high
Log source: product windows, category process_creation
Author: Cian Heasley, Florian Roth (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects processes spawned from web servers (PHP, Tomcat, IIS, etc.) that perform reconnaissance looking for the existence of popular scripting tools (perl, python, wget) on the system via the help commands

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1505.003` Server Software Component: Web Shell

Event coverage

Provider	Event	Title
Sysmon	Event ID 1	Process creation
Security-Auditing	Event ID 4688	A new process has been created.

Rule body yaml

title: Webshell Tool Reconnaissance Activity
id: f64e5c19-879c-4bae-b471-6d84c8339677
status: test
description: |
    Detects processes spawned from web servers (PHP, Tomcat, IIS, etc.) that perform reconnaissance looking for the existence of popular scripting tools (perl, python, wget) on the system via the help commands
references:
    - https://ragged-lab.blogspot.com/2020/07/webshells-automating-reconnaissance.html
author: Cian Heasley, Florian Roth (Nextron Systems)
date: 2020-07-22
modified: 2023-11-09
tags:
    - attack.persistence
    - attack.t1505.003
logsource:
    category: process_creation
    product: windows
detection:
    selection_webserver_image:
        ParentImage|endswith:
            - '\caddy.exe'
            - '\httpd.exe'
            - '\nginx.exe'
            - '\php-cgi.exe'
            - '\w3wp.exe'
            - '\ws_tomcatservice.exe'
    selection_webserver_characteristics_tomcat1:
        ParentImage|endswith:
            - '\java.exe'
            - '\javaw.exe'
        ParentImage|contains:
            - '-tomcat-'
            - '\tomcat'
    selection_webserver_characteristics_tomcat2:
        ParentImage|endswith:
            - '\java.exe'
            - '\javaw.exe'
        CommandLine|contains:
            - 'CATALINA_HOME'
            - 'catalina.jar'
    selection_recon:
        CommandLine|contains:
            - 'perl --help'
            - 'perl -h'
            - 'python --help'
            - 'python -h'
            - 'python3 --help'
            - 'python3 -h'
            - 'wget --help'
    condition: 1 of selection_webserver_* and selection_recon
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: `condition`

1 of selection_webserver_* and selection_recon

Stage 1: `selection_webserver_image`

selection_webserver_image:
    ParentImage|endswith:
        - '\caddy.exe'
        - '\httpd.exe'
        - '\nginx.exe'
        - '\php-cgi.exe'
        - '\w3wp.exe'
        - '\ws_tomcatservice.exe'

Stage 2: `selection_webserver_characteristics_tomcat1`

selection_webserver_characteristics_tomcat1:
    ParentImage|endswith:
        - '\java.exe'
        - '\javaw.exe'
    ParentImage|contains:
        - '-tomcat-'
        - '\tomcat'

Stage 3: `selection_webserver_characteristics_tomcat2`

selection_webserver_characteristics_tomcat2:
    ParentImage|endswith:
        - '\java.exe'
        - '\javaw.exe'
    CommandLine|contains:
        - 'CATALINA_HOME'
        - 'catalina.jar'

Stage 4: `selection_recon`

selection_recon:
    CommandLine|contains:
        - 'perl --help'
        - 'perl -h'
        - 'python --help'
        - 'python -h'
        - 'python3 --help'
        - 'python3 -h'
        - 'wget --help'

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	`CATALINA_HOME` corpus 3 (sigma 3) `catalina.jar` corpus 3 (sigma 3) `perl --help` `perl -h` `python --help` `python -h` `python3 --help` `python3 -h` `wget --help`
`ParentImage`	ends_with	`\caddy.exe` corpus 4 (sigma 4) `\httpd.exe` corpus 6 (sigma 6) `\java.exe` corpus 8 (sigma 8) `\javaw.exe` corpus 7 (sigma 7) `\nginx.exe` corpus 6 (sigma 6) `\php-cgi.exe` corpus 6 (sigma 6) `\w3wp.exe` corpus 12 (sigma 12) `\ws_tomcatservice.exe` corpus 6 (sigma 6)
`ParentImage`	match	`-tomcat-` corpus 4 (sigma 4) `\tomcat` corpus 6 (sigma 6)

`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)

Webshell Tool Reconnaissance Activity

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: `condition`

Stage 1: `selection_webserver_image`

Stage 2: `selection_webserver_characteristics_tomcat1`

Stage 3: `selection_webserver_characteristics_tomcat2`

Stage 4: `selection_recon`

Indicators

Keyboard shortcuts

Search operators

Webshell Tool Reconnaissance Activity

MITRE ATT&CK coverage

Event coverage

Rule body yaml

Stages and Predicates

Stage 0: condition

Stage 1: selection_webserver_image

Stage 2: selection_webserver_characteristics_tomcat1

Stage 3: selection_webserver_characteristics_tomcat2

Stage 4: selection_recon

Indicators

Stage 0: `condition`

Stage 1: `selection_webserver_image`

Stage 2: `selection_webserver_characteristics_tomcat1`

Stage 3: `selection_webserver_characteristics_tomcat2`

Stage 4: `selection_recon`