Corelight - Possible Webshell (Rare PUT or POST)

Status: available
Severity: medium
Time window: 1h
Group by: id_orig_h, uri
Source: github.com/Azure/Azure-Sentinel

'Detects rare post requests to a single webserver location.'

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1505` Server Software Component

Rule body kusto

id: db662e49-6e34-4d10-9d3c-5d04b5479658
name: Corelight - Possible Webshell (Rare PUT or POST)
description: |
  'Detects rare post requests to a single webserver location.'
severity: Medium
status: Available
requiredDataConnectors:
  - connectorId: Corelight
    dataTypes:
      - Corelight_v2_http
      - corelight_http
queryFrequency: 1h
queryPeriod: 1h
triggerOperator: gt
triggerThreshold: 0
tactics:
  - Persistence
relevantTechniques:
  - T1505
query: |
  let threshold = 3;
  corelight_http
  | where method in~ ('POST', 'PUT')
  | where toint(status_code) !between (400 .. 499)
  | where request_body_len != 0 or response_body_len != 0
  | extend fe = extract(@'.*(\.\w+)$', 1, uri)
  | where fe in~ ('.aspx', '.asp', '.php', '.jsp', '.jspx', '.war', '.ashx', '.asmx', '.ascx', '.asx', '.cshtml', '.cfm', '.cfc', '.cfml', '.wss', '.do', '.action', '.pl', '.plx', '.pm', '.xs', '.t', '.pod', '.php-s', '.pht', '.phar', '.phps', '.php7', '.php5', '.php4', '.php3', '.phtml', '.py', '.rb', '.rhtml', '.cgi', '.dll', '.ayws', '.cgi', '.erb', '.rjs', '.hta', '.htc', '.cs', '.kt', '.lua', '.vbhtml')
  | summarize count() by uri, id_orig_h
  | where count_ < threshold
entityMappings:
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: id_orig_h
version: 2.1.0
kind: Scheduled

Stages and Predicates

Parameters

let threshold = 3;

Stage 1: `source`

corelight_http

Stage 2: `where`

| where method in~ ('POST', 'PUT')

Stage 3: `where`

| where toint(status_code) !between (400 .. 499)

Stage 4: `where`

| where request_body_len != 0 or response_body_len != 0

Stage 5: `extend`

| extend fe = extract(@'.*(\.\w+)$', 1, uri)

Stage 6: `where`

| where fe in~ ('.aspx', '.asp', '.php', '.jsp', '.jspx', '.war', '.ashx', '.asmx', '.ascx', '.asx', '.cshtml', '.cfm', '.cfc', '.cfml', '.wss', '.do', '.action', '.pl', '.plx', '.pm', '.xs', '.t', '.pod', '.php-s', '.pht', '.phar', '.phps', '.php7', '.php5', '.php4', '.php3', '.phtml', '.py', '.rb', '.rhtml', '.cgi', '.dll', '.ayws', '.cgi', '.erb', '.rjs', '.hta', '.htc', '.cs', '.kt', '.lua', '.vbhtml')

Stage 7: `summarize`

| summarize count() by uri, id_orig_h

Stage 8: `where`

| where count_ < threshold

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
`count_`	lt	`3` transforms: `cased`
`fe`	in	`.action` `.ascx` `.ashx` `.asmx` `.asp` `.aspx` `.asx` `.ayws` `.cfc` `.cfm` `.cfml` `.cgi` `.cs` `.cshtml` `.dll` `.do` `.erb` `.hta` `.htc` `.jsp` `.jspx` `.kt` `.lua` `.phar` `.php` `.php-s` `.php3` `.php4` `.php5` `.php7` `.phps` `.pht` `.phtml` `.pl` `.plx` `.pm` `.pod` `.py` `.rb` `.rhtml` `.rjs` `.t` `.vbhtml` `.war` `.wss` `.xs`
`method`	in	`POST` `PUT`
`request_body_len`	ne	`0` transforms: `cased`
`response_body_len`	ne	`0` transforms: `cased`

Output fields

Fields the rule emits when it matches. Chronicle authors list these in the outcome block; they appear on the detection and $risk_score drives alerting. Sentinel / Defender XDR rules build them up through project / summarize / extend stages. Sentinel maps these into alert fields via entityMappings and customDetails; Defender XDR custom detections surface them as alert fields directly.

Field	Source
`id_orig_h`	`summarize`
`uri`	`summarize`

`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)

Corelight - Possible Webshell (Rare PUT or POST)

MITRE ATT&CK coverage

Rule body kusto

Stages and Predicates

Parameters

Stage 1: `source`

Stage 2: `where`

Stage 3: `where`

Stage 4: `where`

Stage 5: `extend`

Stage 6: `where`

Stage 7: `summarize`

Stage 8: `where`

Indicators

Output fields

Keyboard shortcuts

Search operators

Corelight - Possible Webshell (Rare PUT or POST)

MITRE ATT&CK coverage

Rule body kusto

Stages and Predicates

Parameters

Stage 1: source

Stage 2: where

Stage 3: where

Stage 4: where

Stage 5: extend

Stage 6: where

Stage 7: summarize

Stage 8: where

Indicators

Output fields

Stage 1: `source`

Stage 2: `where`

Stage 3: `where`

Stage 4: `where`

Stage 5: `extend`

Stage 6: `where`

Stage 7: `summarize`

Stage 8: `where`