GCP Cloud Storage Buckets Modified Or Deleted

Severity: low
Entities: ip_addresses
Log types: GCP.AuditLog
Tags: GCP, Google Cloud Storage, Defense Evasion:Impair Defenses, Impact:Data Encrypted for Impact, Ransomware
Reference: https://cloud.google.com/storage/docs/json_api/v1/buckets/update
Source: github.com/panther-labs/panther-analysis

Detects when a GCS bucket configuration is updated or deleted. Bucket configuration changes can be part of a ransomware attack, such as disabling security settings to prevent data recovery.

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1562` Impair Defenses
Impact	`T1486` Data Encrypted for Impact

Rule body yaml

AnalysisType: rule
DisplayName: "GCP Cloud Storage Buckets Modified Or Deleted"
Enabled: true
Filename: gcp_cloud_storage_buckets_modified_or_deleted.py
Description: >
  Detects when a GCS bucket configuration is updated or deleted. Bucket configuration changes can be
  part of a ransomware attack, such as disabling security settings to prevent data recovery.
Runbook: |
  1. Query GCP Audit logs for all bucket operations by the principal email in the 24 hours before and after this alert
  2. Check if the source IP is associated with known cloud provider IP ranges, VPN endpoints, or matches the user's typical access patterns
  3. Identify what specific configuration was changed (encryption, retention, versioning, lifecycle policies)
  4. Search for related KMS key changes or IAM policy modifications on the same bucket in the past 6 hours
  5. Look for bulk object operations (rewrite, copy, delete) on this bucket following the configuration change
Reference: https://cloud.google.com/storage/docs/json_api/v1/buckets/update
Tags:
  - GCP
  - Google Cloud Storage
  - Defense Evasion:Impair Defenses
  - Impact:Data Encrypted for Impact
  - Ransomware
Reports:
  MITRE ATT&CK:
    - TA0005:T1562
    - TA0040:T1486
SummaryAttributes:
  - severity
  - p_any_ip_addresses
  - p_any_emails
Severity: Low
Tests:
  - ExpectedResult: false
    Log:
      insertid: ezyd47c12y
      logname: projects/gcp-project1/logs/cloudaudit.googleapis.com%2Factivity
      p_any_ip_addresses:
        - 1.2.3.4
      p_event_time: "2023-03-09 16:41:30.524"
      p_log_type: GCP.AuditLog
      p_parse_time: "2023-03-09 16:44:14.617"
      p_row_id: "1234567909689348911"
      p_source_id: 4fc88a5a-2d51-4279-9c4a-08fa7cc52566
      p_source_label: gcplogsource
      protoPayload:
        at_sign_type: type.googleapis.com/google.cloud.audit.AuditLog
        authenticationInfo:
          principalEmail: john@justice.org
        authorizationInfo:
          - granted: true
            permission: logging.sinks.update
            resource: projects/gcp-project1/sinks/log-sink
            resourceAttributes:
              name: projects/gcp-project1/sinks/log-sink
              service: logging.googleapis.com
        methodName: google.logging.v2.ConfigServiceV2.UpdateSink
        request:
          "@type": type.googleapis.com/google.logging.v2.UpdateSinkRequest
          sink:
            destination: pubsub.googleapis.com/projects/gcp-project1/topics/gcp-topic1
            exclusions:
              - filter: protoPayload.serviceName = 'k8s.io
                name: excludek8s
            name: log-sink
            writerIdentity: serviceAccount:denethor@lotr.com
          sinkName: projects/gcp-project1/sinks/log-sink
          uniqueWriterIdentity: true
          updateMask: exclusions
        requestMetadata:
          callerIP: 1.2.3.4
          callerSuppliedUserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/1.2.3.4 Safari/537.36,gzip(gfe),gzip(gfe)
          destinationAttributes: {}
          requestAttributes:
            auth: {}
            time: "2023-03-09T16:41:30.540045105Z"
        resourceName: projects/gcp-project1/sinks/log-sink
        serviceName: logging.googleapis.com
        status: {}
      receivetimestamp: "2023-03-09 16:41:32.21"
      resource:
        labels:
          destination: ""
          name: log-sink
          project_id: gcp-project1
        type: logging_sink
      severity: NOTICE
      timestamp: "2023-03-09 16:41:30.524"
    Name: other event
  - ExpectedResult: true
    Log:
      insertId: asdf1234asdfg
      logName: projects/gcp-project1/logs/cloudaudit.googleapis.com%2Factivity
      p_any_ip_addresses:
        - 1.2.3.4
      p_event_time: "2023-03-09 10:05:23.603"
      p_log_type: GCP.AuditLog
      p_parse_time: "2023-03-09 10:07:14.731"
      p_row_id: 7ad218d42253b7e6f78cc0ed1635
      p_source_id: 4fc88a5a-2d51-4279-9c4a-08fa7cc52566
      p_source_label: gcplogsource
      protoPayload:
        at_sign_type: type.googleapis.com/google.cloud.audit.AuditLog
        authenticationInfo:
          principalEmail: user@company.io
        authorizationInfo:
          - granted: true
            permission: storage.buckets.update
            resource: projects/_/buckets/my-bucket
            resourceAttributes: {}
        methodName: storage.buckets.update
        requestMetadata:
          callerIP: 1.2.3.4
          callerSuppliedUserAgent: apitools Python/3.9.11 gsutil/5.11 (darwin) analytics/enabled interactive/True command/notification google-cloud-sdk/394.0.0,gzip(gfe)
          destinationAttributes: {}
          requestAttributes:
            auth: {}
            time: "2023-03-09T10:05:23.610372568Z"
        resourceName: projects/_/buckets/my-bucket
        serviceName: storage.googleapis.com
        status: {}
      receiveTimestamp: "2023-03-09 10:05:25.146"
      resource:
        labels:
          bucket_name: my-bucket
          location: us-east1
          project_id: gcp-project1
        type: gcs_bucket
      severity: NOTICE
      timestamp: "2023-03-09 10:05:23.603"
    Name: bucket update
DedupPeriodMinutes: 60
LogTypes:
  - GCP.AuditLog
RuleID: "GCP.Cloud.Storage.Buckets.Modified.Or.Deleted"
Threshold: 1

Detection logic

Condition

protoPayload.serviceName eq "storage.googleapis.com"
protoPayload.methodName in ["storage.buckets.delete", "storage.buckets.update"]
severity ne "ERROR"

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
`protoPayload.methodName`	in	`storage.buckets.delete` `storage.buckets.update`
`protoPayload.serviceName`	eq	`storage.googleapis.com`
`severity`	ne	`ERROR`

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
`actor`	`protoPayload.authenticationInfo.principalEmail`
`bucket`	`resource.labels.bucket_name`
`source_ip`	`protoPayload.requestMetadata.callerIp`
`user_agent`	`protoPayload.requestMetadata.callerSuppliedUserAgent`
`project`	`resource.labels.project_id`
`methodName`	`protoPayload.methodName`

`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)