Azure Storage SAS Token Access from External IP

Severity: low
Group by: properties.accountName
Log types: Azure.MonitorActivity
Tags: Exfiltration, Credential Access, Storm-0501, Defender for Cloud, SAS Token
Reference: https://learn.microsoft.com/en-us/azure/defender-for-cloud/alerts-azure-storage
Source: github.com/panther-labs/panther-analysis

Detects SAS token usage from external public IPs by parsing the signature parameter in storage URIs. Storm-0501 uses stolen SAS tokens from external C2 infrastructure for data exfiltration. Replicates Defender for Cloud alert 'Storage.Blob_AccountSas.InternalSasUsedExternally'.

MITRE ATT&CK coverage

Tactic	Techniques
Credential Access	`T1552.001` Unsecured Credentials: Credentials In Files
Exfiltration	`T1567` Exfiltration Over Web Service

Rule body yaml

AnalysisType: rule
Filename: azure_storage_sas_external_access.py
RuleID: "Azure.MonitorActivity.Storage.SASTokenExternalAccess"
DisplayName: "Azure Storage SAS Token Access from External IP"
Enabled: true
LogTypes:
  - Azure.MonitorActivity
Severity: Low
DedupPeriodMinutes: 60
Description: >
  Detects SAS token usage from external public IPs by parsing the signature parameter in storage URIs.
  Storm-0501 uses stolen SAS tokens from external C2 infrastructure for data exfiltration.
  Replicates Defender for Cloud alert 'Storage.Blob_AccountSas.InternalSasUsedExternally'.
Reports:
  MITRE ATT&CK:
    - TA0010:T1567 # Exfiltration: Exfiltration Over Web Service
    - TA0006:T1552.001 # Credential Access: Unsecured Credentials - Credentials In Files
Reference: https://learn.microsoft.com/en-us/azure/defender-for-cloud/alerts-azure-storage
Tags:
  - Exfiltration
  - Credential Access
  - Storm-0501
  - Defender for Cloud
  - SAS Token
Runbook: |
  1. Query Azure Monitor Activity logs for SAS token generation operations (Microsoft.Storage/storageAccounts/listAccountSas/action) by the same identity in the 24 hours before this access to identify when the token was created and by whom
  2. Find all storage operations (GetBlob, ListBlobs, DeleteBlob) from the callerIpAddress in the 6 hours before and after the alert to assess if this is isolated access or part of bulk exfiltration
  3. Check if the callerIpAddress has accessed this storage account in the past 90 days to establish if this external IP is expected
  4. Review Azure Audit logs for authentication events from the callerIpAddress in the 48 hours before the alert to identify potential account compromise or credential theft
  5. Search for other alerts with the same callerIpAddress across all storage accounts in the past 7 days to identify if this is targeted or widespread
SummaryAttributes:
  - callerIpAddress
  - properties:accountName
  - operationName
Tests:
  - Name: SAS Token from External IP - Read Operation
    ExpectedResult: true
    Log:
      {
        "time": "2025-01-28T15:30:00.0000000Z",
        "category": "StorageRead",
        "operationName": "GetBlob",
        "callerIpAddress": "8.8.8.8:45123",
        "statusCode": 200,
        "uri": "https://criticaldata001.blob.core.windows.net/backups/data.zip?sv=2021-12-02&ss=b&srt=sco&sp=rl&se=2025-12-31T23:59:59Z&sig=SIGNATURE_HERE",
        "properties": {
          "accountName": "criticaldata001",
          "objectKey": "/criticaldata001/backups/data.zip",
          "userAgentHeader": "python-requests/2.31.0",
          "metricResponseType": "Success"
        },
        "p_log_type": "Azure.MonitorActivity"
      }
  - Name: SAS Token from External IP - Delete Operation
    ExpectedResult: true
    Log:
      {
        "time": "2025-01-28T16:00:00.0000000Z",
        "category": "StorageDelete",
        "operationName": "DeleteBlob",
        "callerIpAddress": "1.1.1.1:12345",
        "statusCode": 202,
        "uri": "https://proddata.blob.core.windows.net/financial/records.xlsx?sv=2021-12-02&sp=rwdl&sig=ATTACKER_SIG",
        "properties": {
          "accountName": "proddata",
          "objectKey": "/proddata/financial/records.xlsx",
          "userAgentHeader": "curl/7.88.0",
          "metricResponseType": "Success"
        },
        "p_log_type": "Azure.MonitorActivity"
      }
  - Name: SAS Token from Internal IP 
    ExpectedResult: false
    Log:
      {
        "time": "2025-01-28T16:30:00.0000000Z",
        "category": "StorageWrite",
        "operationName": "PutBlob",
        "callerIpAddress": "10.158.74.16:36683",
        "statusCode": 201,
        "uri": "https://internaldata.blob.core.windows.net/logs/app.log?sv=2021-12-02&sp=w&sig=INTERNAL_SIG",
        "properties": {
          "accountName": "internaldata",
          "objectKey": "/internaldata/logs/app.log",
          "userAgentHeader": "Azure-Storage/1.0",
          "metricResponseType": "Success"
        },
        "p_log_type": "Azure.MonitorActivity"
      }
  - Name: Storage Account Key Auth from External IP 
    ExpectedResult: false
    Log:
      {
        "time": "2025-01-28T17:00:00.0000000Z",
        "category": "StorageRead",
        "operationName": "GetBlob",
        "callerIpAddress": "9.9.9.9:55555",
        "statusCode": 200,
        "uri": "https://publicdata.blob.core.windows.net/downloads/file.pdf",
        "properties": {
          "accountName": "publicdata",
          "objectKey": "/publicdata/downloads/file.pdf",
          "userAgentHeader": "Microsoft.Azure.Storage/9.0",
          "metricResponseType": "Success"
        },
        "identity": {
          "type": "AccountKey"
        },
        "p_log_type": "Azure.MonitorActivity"
      }
  - Name: Failed SAS Token Access 
    ExpectedResult: false
    Log:
      {
        "time": "2025-01-28T17:30:00.0000000Z",
        "category": "StorageRead",
        "operationName": "GetBlob",
        "callerIpAddress": "4.4.4.4:33333",
        "statusCode": 403,
        "statusText": "AuthenticationFailed",
        "uri": "https://securedata.blob.core.windows.net/secrets/key.txt?sv=2021-12-02&sp=r&sig=EXPIRED_SIG",
        "properties": {
          "accountName": "securedata",
          "objectKey": "/securedata/secrets/key.txt",
          "metricResponseType": "AuthenticationFailed"
        },
        "p_log_type": "Azure.MonitorActivity"
      }

Detection logic

Condition

category in ["StorageRead", "StorageWrite", "StorageDelete"]
statusCode in ["200", "201", "202", "204"]
not (uri is_null or uri not contains "sig=")

This rule also runs imperative logic the parser cannot express as a filter; the conditions above are the structured part it could extract.

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

Field	Kind	Excluded values
`uri`	contains	`sig=`
`uri`	is_null	(no value, null check)

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
`category`	in	`StorageDelete` `StorageRead` `StorageWrite`
`statusCode`	in	`200` `201` `202` `204`
`uri`	contains	`sig=`

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
`storage_account`	`properties.accountName`
`operation`	`operationName`
`object_key`	`properties.objectKey`
`user_agent`	`properties.userAgentHeader`
`uri`
`status_code`	`statusCode`
`category`

`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)