Replace brittle managed identity enumeration examples

Author: carlospolop

src/pentesting-cloud/azure-security/az-services/vms/README.md

@@ -889,44 +889,17 @@ However, not every process will necessarily get the same practical result:
 
 Therefore, if a request works from Run Command but fails from SSH, the usual explanation is a difference in OS user, environment, routing, proxy, firewall, or namespace, not a general Azure rule that only agent execution contexts can reach `168.63.129.16`.
 
-### Run Command vs SSH Context
+### Managed Identity Access From Inside the VM
 
-Azure provides multiple ways to execute commands inside a VM, but **they do not run in the same context**.
+The reliable way to use a VM's managed identities is the **IMDS managed identity endpoint** at `169.254.169.254`, not the WireServer `ExtensionsConfig` XML. Scripts that only search `ExtensionsConfig` for `UserAssignedIdentity` nodes are not reliable because:
 
-#### Run Command
+- The VM's managed identity assignment is not guaranteed to be represented as `UserAssignedIdentity` nodes in extension XML.
+- They miss **system-assigned managed identities**.
+- They only find user-assigned identities if the current GoalState/extension data happens to expose the expected XML shape.
 
-Run Command is an Azure feature that executes scripts via the **VM Agent**.
+Microsoft's documented security model is that **all code running on the VM can request tokens for the managed identities available on that VM**. If several user-assigned identities exist, request a specific one with `client_id`, `object_id`, or `msi_res_id`.
 
-- Uses: `Microsoft.Compute/virtualMachines/runCommand/action`
-- Runs through the **Azure VM Agent**
-- Usually runs with elevated local privileges (`root` on Linux or `SYSTEM` on Windows)
-- Can often reach WireServer/GoalState/ExtensionsConfig even when a low-privileged user is blocked by local controls
-
-Example:
-
-```bash
-az vm run-command invoke \
-  --resource-group <rsc-group> \
-  --name <vm-name> \
-  --command-id RunShellScript \
-  --scripts @script.sh
-```
-
-#### SSH Session
-
-When connecting via SSH:
-
-- Runs as a **regular OS user**
-- Uses standard network stack
-- Does **not** have VM Agent privileges by default
-
-As a result:
-
-- Requests to `168.63.129.16` can work from SSH if the guest configuration allows it
-- Requests may fail if blocked by local firewall, proxy, routing, network namespace, or user-level controls
-- GoalState requests require the correct endpoint path and headers
-
-**Script Examples to get attached managed identities:**
+The following examples first request a token. Then they try to read the VM resource from Azure Resource Manager and print its `identity` property. The second step only works if the managed identity has permissions such as `Microsoft.Compute/virtualMachines/read` on the VM.
 
 {{#tabs }}
 {{#tab name="Linux" }}
@@ -935,193 +908,133 @@ As a result:
 #!/usr/bin/env bash
 set -euo pipefail
 
-ws="http://168.63.129.16"
-
-echo "[*] Getting Goal State..."
+imds="http://169.254.169.254/metadata"
+api_version="2021-02-01"
+resource="${1:-https://management.azure.com/}"
 
-goal_urls=(
-  "$ws/machine?comp=goalstate"
-  "$ws/machine/?comp=goalstate"
-)
+# Optional. Examples:
+#   export MSI_SELECTOR='client_id=<client-id>'
+#   export MSI_SELECTOR='object_id=<principal-id>'
+#   export MSI_SELECTOR='msi_res_id=/subscriptions/.../userAssignedIdentities/name'
+selector="${MSI_SELECTOR:-}"
 
-goal_xml=""
-for url in "${goal_urls[@]}"; do
-  if goal_xml="$(curl -fsS -H "x-ms-version: 2012-11-30" "$url" 2>/dev/null)"; then
-    echo "[+] GoalState OK via $url"
-    break
-  fi
-done
+urlencode() {
+  python3 -c 'import sys, urllib.parse; print(urllib.parse.quote(sys.argv[1], safe=""))' "$1"
+}
 
-if [[ -z "$goal_xml" ]]; then
-  echo "[-] No GoalState endpoint responded"
-  exit 1
+token_url="$imds/identity/oauth2/token?api-version=$api_version&resource=$(urlencode "$resource")"
+if [[ -n "$selector" ]]; then
+  token_url="$token_url&$selector"
 fi
 
-ext_url="$(
-  GOAL_XML="$goal_xml" python3 - <<'PY'
-import os
-import xml.etree.ElementTree as ET
+echo "[*] Requesting managed identity token for: $resource"
+token_json="$(curl -fsS --noproxy "*" -H "Metadata:true" "$token_url")"
+
+access_token="$(
+  TOKEN_JSON="$token_json" python3 - <<'PY'
+import json, os
+print(json.loads(os.environ["TOKEN_JSON"])["access_token"])
+PY
+)"
 
-xml = os.environ["GOAL_XML"].strip()
-root = ET.fromstring(xml)
+TOKEN="$access_token" python3 - <<'PY'
+import base64, json, os
 
-def lname(tag):
-    return tag.rsplit("}", 1)[-1]
+token = os.environ["TOKEN"]
+payload = token.split(".")[1]
+payload += "=" * (-len(payload) % 4)
+claims = json.loads(base64.urlsafe_b64decode(payload))
 
-for el in root.iter():
-    if lname(el.tag) == "ExtensionsConfig" and (el.text or "").strip():
-        print(el.text.strip())
-        break
+print("[+] Token acquired")
+for key in ("tid", "appid", "oid", "xms_mirid"):
+    if key in claims:
+        print(f"    {key}: {claims[key]}")
 PY
-)"
 
-if [[ -z "$ext_url" ]]; then
-  echo "[-] No ExtensionsConfig URL found in GoalState"
-  echo "[*] Identity-like nodes seen in GoalState:"
-  GOAL_XML="$goal_xml" python3 - <<'PY'
-import os
-import xml.etree.ElementTree as ET
-
-xml = os.environ["GOAL_XML"].strip()
-root = ET.fromstring(xml)
-
-def lname(tag):
-    return tag.rsplit("}", 1)[-1]
-
-found = False
-for el in root.iter():
-    name = lname(el.tag)
-    if "Identity" in name:
-        found = True
-        text = (el.text or "").strip()
-        print(f"<{name}>{text}</{name}>")
-
-if not found:
-    print("    (none)")
+echo "[*] Trying to read the VM identity property through ARM..."
+compute_json="$(curl -fsS --noproxy "*" -H "Metadata:true" "$imds/instance/compute?api-version=$api_version")"
+vm_id="$(
+  COMPUTE_JSON="$compute_json" python3 - <<'PY'
+import json, os
+print(json.loads(os.environ["COMPUTE_JSON"])["resourceId"])
 PY
-  exit 0
-fi
+)"
 
-echo "[*] Getting ExtensionsConfig..."
-ext_xml="$(curl -fsS -H "x-ms-version: 2012-11-30" "$ext_url")"
-
-EXT_XML="$ext_xml" python3 - <<'PY'
-import os
-import xml.etree.ElementTree as ET
-
-xml = os.environ["EXT_XML"].strip()
-root = ET.fromstring(xml)
-
-def lname(tag):
-    return tag.rsplit("}", 1)[-1]
-
-ids = [el for el in root.iter() if lname(el.tag) == "UserAssignedIdentity"]
-
-if not ids:
-    print("[-] No UserAssignedIdentity nodes found")
-    print("[*] Identity-like nodes present in ExtensionsConfig:")
-    shown = False
-    for el in root.iter():
-        name = lname(el.tag)
-        if "Identity" in name:
-            shown = True
-            text = (el.text or "").strip()
-            attrs = " ".join(f'{k}="{v}"' for k, v in el.attrib.items())
-            if attrs:
-                print(f"    <{name} {attrs}>{text}</{name}>")
-            else:
-                print(f"    <{name}>{text}</{name}>")
-    if not shown:
-        print("    (none)")
-    raise SystemExit(0)
-
-for idnode in ids:
-    client_id = ""
-    object_id = ""
-    resource_id = ""
-
-    for child in idnode.iter():
-        name = lname(child.tag)
-        text = (child.text or "").strip()
-        if name == "IdentityClientId":
-            client_id = text
-        elif name == "IdentityObjectId":
-            object_id = text
-        elif name == "IdentityResourceId":
-            resource_id = text
-
-    print()
-    print("[+] Managed Identity:")
-    print(f"    ClientId   : {client_id}")
-    print(f"    ObjectId   : {object_id}")
-    print(f"    ResourceId : {resource_id}")
+arm_url="https://management.azure.com${vm_id}?api-version=2024-07-01"
+if vm_json="$(curl -fsS -H "Authorization: Bearer $access_token" "$arm_url" 2>/dev/null)"; then
+  VM_JSON="$vm_json" python3 - <<'PY'
+import json, os
+vm = json.loads(os.environ["VM_JSON"])
+print(json.dumps(vm.get("identity", {}), indent=2))
 PY
+else
+  echo "[-] Could not read the VM resource with this identity. The token may still be valid, but it lacks ARM read permissions on the VM."
+fi
 ```
 
 {{#endtab }}
 
 {{#tab name="Windows" }}
 
-```bash
-$ws = "http://168.63.129.16"
-$h  = @{
-    "x-ms-version" = "2012-11-30"
+```powershell
+$imds = "http://169.254.169.254/metadata"
+$apiVersion = "2021-02-01"
+$resource = "https://management.azure.com/"
+
+# Optional. Examples:
+#   $env:MSI_SELECTOR = "client_id=<client-id>"
+#   $env:MSI_SELECTOR = "object_id=<principal-id>"
+#   $env:MSI_SELECTOR = "msi_res_id=/subscriptions/.../userAssignedIdentities/name"
+$selector = $env:MSI_SELECTOR
+
+function Invoke-Imds {
+    param([string]$Uri)
+
+    $params = @{
+        Method = "GET"
+        Uri = $Uri
+        Headers = @{ Metadata = "true" }
+        UseBasicParsing = $true
+    }
+    if ((Get-Command Invoke-RestMethod).Parameters.ContainsKey("NoProxy")) {
+        $params.NoProxy = $true
+    }
+    Invoke-RestMethod @params
 }
 
-Write-Host "[*] Getting Goal State..." -ForegroundColor Cyan
-
-$goalUrls = @(
-    "$ws/machine?comp=goalstate",
-    "$ws/machine/?comp=goalstate"
-)
-
-$gs = $null
+function Decode-JwtPayload {
+    param([string]$Token)
 
-foreach ($url in $goalUrls) {
-    try {
-        $gs = Invoke-WebRequest -Uri $url -Headers $h -UseBasicParsing -ErrorAction Stop
-        Write-Host "[+] GoalState OK via $url" -ForegroundColor Green
-        break
-    } catch {}
+    $payload = $Token.Split(".")[1].Replace("-", "+").Replace("_", "/")
+    switch ($payload.Length % 4) {
+        2 { $payload += "==" }
+        3 { $payload += "=" }
+    }
+    [Text.Encoding]::UTF8.GetString([Convert]::FromBase64String($payload)) | ConvertFrom-Json
 }
 
-if (-not $gs) {
-    Write-Host "[-] No GoalState endpoint responded" -ForegroundColor Red
-    return
+$encodedResource = [uri]::EscapeDataString($resource)
+$tokenUri = "$imds/identity/oauth2/token?api-version=$apiVersion&resource=$encodedResource"
+if ($selector) {
+    $tokenUri = "$tokenUri&$selector"
 }
 
-[xml]$xml = $gs.Content
-$cfg = $xml.GoalState.Container.RoleInstanceList.RoleInstance.Configuration
+Write-Host "[*] Requesting managed identity token for: $resource"
+$tokenResponse = Invoke-Imds -Uri $tokenUri
+$claims = Decode-JwtPayload -Token $tokenResponse.access_token
 
-$extUrl = $cfg.ExtensionsConfig
+Write-Host "[+] Token acquired"
+$claims | Select-Object tid, appid, oid, xms_mirid | Format-List
 
-Write-Host "[*] Getting ExtensionsConfig..." -ForegroundColor Cyan
+Write-Host "[*] Trying to read the VM identity property through ARM..."
+$compute = Invoke-Imds -Uri "$imds/instance/compute?api-version=$apiVersion"
+$armUri = "https://management.azure.com$($compute.resourceId)?api-version=2024-07-01"
 
 try {
-    $ext = Invoke-WebRequest -Uri $extUrl -Headers $h -UseBasicParsing -ErrorAction Stop
-    [xml]$extXml = $ext.Content
+    $vm = Invoke-RestMethod -Method GET -Uri $armUri -Headers @{ Authorization = "Bearer $($tokenResponse.access_token)" } -UseBasicParsing
+    $vm.identity | ConvertTo-Json -Depth 20
 } catch {
-    Write-Host "[-] Error getting ExtensionsConfig" -ForegroundColor Red
-    return
-}
-
-# Extract Managed Identity info
-$ids = $extXml.SelectNodes("//UserAssignedIdentity")
-
-if (!$ids) {
-    Write-Host "[-] No User Assigned Identities found" -ForegroundColor Red
-    return
-}
-
-foreach ($id in $ids) {
-    $clientId   = $id.IdentityClientId
-    $objectId   = $id.IdentityObjectId
-    $resourceId = $id.IdentityResourceId
-
-    Write-Host "`n[+] Managed Identity:" -ForegroundColor Green
-    Write-Host "    ClientId   : $clientId"
-    Write-Host "    ObjectId   : $objectId"
-    Write-Host "    ResourceId : $resourceId"
+    Write-Host "[-] Could not read the VM resource with this identity. The token may still be valid, but it lacks ARM read permissions on the VM."
 }
 ```
 
@@ -1158,12 +1071,11 @@ foreach ($id in $ids) {
 - [https://learn.microsoft.com/en-us/azure/virtual-machines/overview](https://learn.microsoft.com/en-us/azure/virtual-machines/overview)
 - [https://hausec.com/2022/05/04/azure-virtual-machine-execution-techniques/](https://hausec.com/2022/05/04/azure-virtual-machine-execution-techniques/)
 - [https://learn.microsoft.com/en-us/azure/virtual-machines/instance-metadata-service](https://learn.microsoft.com/en-us/azure/virtual-machines/instance-metadata-service)
+- [https://learn.microsoft.com/en-us/entra/identity/managed-identities-azure-resources/how-to-use-vm-token](https://learn.microsoft.com/en-us/entra/identity/managed-identities-azure-resources/how-to-use-vm-token)
 - [https://learn.microsoft.com/en-us/azure/virtual-network/what-is-ip-address-168-63-129-16](https://learn.microsoft.com/en-us/azure/virtual-network/what-is-ip-address-168-63-129-16)
 - [https://learn.microsoft.com/en-us/azure/virtual-machines/linux/no-agent](https://learn.microsoft.com/en-us/azure/virtual-machines/linux/no-agent)
 - [https://learn.microsoft.com/en-us/azure/virtual-machines/run-command](https://learn.microsoft.com/en-us/azure/virtual-machines/run-command)
 - [https://learn.microsoft.com/en-us/azure/virtual-machines/extensions/agent-linux](https://learn.microsoft.com/en-us/azure/virtual-machines/extensions/agent-linux)
 - [https://www.cybercx.com.au/blog/azure-ssrf-metadata/](https://www.cybercx.com.au/blog/azure-ssrf-metadata/)
 
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