Discord CDN Risky File Download

Status: available
Severity: medium
Time window: 1d
Group by: DeviceProduct, DiscordServerId, dcount_RequestURL, max_TimeGenerated, min_TimeGenerated, set_DeviceAction, set_RequestURL, set_SourceIP, set_SourceUserName
Source: github.com/Azure/Azure-Sentinel

'Identifies callouts to Discord CDN addresses for risky file extensions. This detection will trigger when a callout for a risky file is made to a discord server that has only been seen once in your environment. Unique discord servers are identified using the server ID that is included in the request URL (DiscordServerId in query). Discord CDN has been used in multiple campaigns to download additional payloads'

MITRE ATT&CK coverage

Tactic	Techniques
Command & Control	`T1071.001` Application Layer Protocol: Web Protocols

Rule body kusto

id: 010bd98c-a6be-498c-bdcd-502308c0fdae
name: Discord CDN Risky File Download
description: |
  'Identifies callouts to Discord CDN addresses for risky file extensions. This detection will trigger when a callout for a risky file is made to a discord server that has only been seen once in your environment. Unique discord servers are identified using the server ID that is included in the request URL (DiscordServerId in query). Discord CDN has been used in multiple campaigns to download additional payloads'
severity: Medium
status: Available
requiredDataConnectors:
  - connectorId: CefAma
    dataTypes:
      - CommonSecurityLog
queryFrequency: 1d
queryPeriod: 1d
triggerOperator: gt
triggerThreshold: 0
tactics:
  - CommandAndControl
relevantTechniques:
  - T1071.001
tags:
  - Discord
query: |
  let connectionThreshold = 1;
  let riskyExtensions = dynamic([".bin",".exe",".dll",".bin",".msi"]);
  CommonSecurityLog
  | where DeviceVendor =~ "ZScaler"
  | where RequestURL has_any("media.discordapp.net", "cdn.discordapp.com")
  | where RequestURL has "attachments"
  | where DeviceAction !~ "blocked"
  | extend DiscordServerId = extract(@"\/attachments\/([0-9]+)\/", 1, RequestURL)
  | summarize dcount(RequestURL), make_set(SourceUserName), make_set(SourceIP), make_set(RequestURL), min(TimeGenerated), max(TimeGenerated), make_set(DeviceAction) by DiscordServerId, DeviceProduct
  | where dcount_RequestURL <= connectionThreshold
  | mv-expand set_SourceUserName to typeof(string), set_RequestURL to typeof(string), set_DeviceAction to typeof(string), set_SourceIP to typeof(string)
  | summarize by DiscordServerId, DeviceProduct, dcount_RequestURL, set_SourceUserName, min_TimeGenerated, max_TimeGenerated, set_DeviceAction, set_SourceIP, set_RequestURL
  | project StartTime=min_TimeGenerated, EndTime=max_TimeGenerated, DeviceActionTaken=set_DeviceAction, DeviceProduct, SourceUser=set_SourceUserName, SourceIP=set_SourceIP, RequestURL=set_RequestURL
  | where RequestURL has_any (riskyExtensions)
entityMappings:
  - entityType: Account
    fieldMappings:
      - identifier: FullName
        columnName: SourceUser
  - entityType: IP
    fieldMappings:
      - identifier: Address
        columnName: SourceIP
  - entityType: URL
    fieldMappings:
      - identifier: Url
        columnName: RequestURL
version: 1.0.4
kind: Scheduled

Stages and Predicates

Parameters

let connectionThreshold = 1;
let riskyExtensions = dynamic([".bin",".exe",".dll",".bin",".msi"]);

Stage 1: `source`

CommonSecurityLog

Stage 2: `where`

| where DeviceVendor =~ "ZScaler"

Stage 3: `where`

| where RequestURL has_any("media.discordapp.net", "cdn.discordapp.com")

Stage 4: `where`

| where RequestURL has "attachments"

Stage 5: `where`

| where DeviceAction !~ "blocked"

Stage 6: `extend`

| extend DiscordServerId = extract(@"\/attachments\/([0-9]+)\/", 1, RequestURL)

Stage 7: `summarize`

| summarize dcount(RequestURL), make_set(SourceUserName), make_set(SourceIP), make_set(RequestURL), min(TimeGenerated), max(TimeGenerated), make_set(DeviceAction) by DiscordServerId, DeviceProduct

Stage 8: `where`

| where dcount_RequestURL <= connectionThreshold

Stage 9: `mv-expand`

| mv-expand set_SourceUserName to typeof(string), set_RequestURL to typeof(string), set_DeviceAction to typeof(string), set_SourceIP to typeof(string)

Stage 10: `summarize`

| summarize by DiscordServerId, DeviceProduct, dcount_RequestURL, set_SourceUserName, min_TimeGenerated, max_TimeGenerated, set_DeviceAction, set_SourceIP, set_RequestURL

Stage 11: `project`

| project StartTime=min_TimeGenerated, EndTime=max_TimeGenerated, DeviceActionTaken=set_DeviceAction, DeviceProduct, SourceUser=set_SourceUserName, SourceIP=set_SourceIP, RequestURL=set_RequestURL

Stage 12: `where`

| where RequestURL has_any (riskyExtensions)

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
`DeviceAction`	ne	`blocked`
`DeviceVendor`	eq	`ZScaler`
`RequestURL`	match	`.bin` `.dll` `.exe` `.msi` `attachments` transforms: `term` `cdn.discordapp.com` `media.discordapp.net`
`dcount_RequestURL`	le	`1` 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
`DeviceActionTaken`	`project`
`DeviceProduct`	`project`
`EndTime`	`project`
`RequestURL`	`project`
`SourceIP`	`project`
`SourceUser`	`project`
`StartTime`	`project`

`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)

Discord CDN Risky File Download

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: `where`

Stage 6: `extend`

Stage 7: `summarize`

Stage 8: `where`

Stage 9: `mv-expand`

Stage 10: `summarize`

Stage 11: `project`

Stage 12: `where`

Indicators

Output fields

Keyboard shortcuts

Search operators

Discord CDN Risky File Download

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: where

Stage 6: extend

Stage 7: summarize

Stage 8: where

Stage 9: mv-expand

Stage 10: summarize

Stage 11: project

Stage 12: where

Indicators

Output fields

Stage 1: `source`

Stage 2: `where`

Stage 3: `where`

Stage 4: `where`

Stage 5: `where`

Stage 6: `extend`

Stage 7: `summarize`

Stage 8: `where`

Stage 9: `mv-expand`

Stage 10: `summarize`

Stage 11: `project`

Stage 12: `where`