GCP Firewall Rule Modified

Severity: low
Group by: protoPayload.authenticationInfo.principalEmail
Log types: GCP.AuditLog
Tags: GCP, Firewall, Networking, Infrastructure
Reference: https://cloud.google.com/firewall/docs/about-firewalls
Source: github.com/panther-labs/panther-analysis

This rule detects modifications to GCP firewall rules.

Rule body yaml

AnalysisType: rule
DedupPeriodMinutes: 90
DisplayName: GCP Firewall Rule Modified
Enabled: true
Filename: gcp_firewall_rule_modified.py
RuleID: "GCP.Firewall.Rule.Modified"
Severity: Low
LogTypes:
  - GCP.AuditLog
Tags:
  - GCP
  - Firewall
  - Networking
  - Infrastructure
Description: >
  This rule detects modifications to GCP firewall rules.
Runbook: >
  Ensure that the rule modification was expected. Firewall rule changes can cause service interruptions or outages.
Reference: https://cloud.google.com/firewall/docs/about-firewalls
Tests:
  - Name: compute.firewalls.update-should-alert
    LogType: GCP.AuditLog
    ExpectedResult: true
    Log:
      {
        "insertid": "-xxxxxxxxxxxx",
        "logname": "projects/test-project-123456/cloudaudit.googleapis.com%2Factivity",
        "operation":
          {
            "first": true,
            "id": "operation-1684869580331-5fc6144d418a9-e1332ca3-59c615ac",
            "producer": "compute.googleapis.com",
          },
        "protoPayload":
          {
            "at_sign_type": "type.googleapis.com/google.cloud.audit.AuditLog",
            "authenticationInfo": { "principalEmail": "user@domain.com" },
            "authorizationInfo":
              [
                {
                  "granted": true,
                  "permission": "compute.firewalls.update",
                  "resourceAttributes":
                    {
                      "name": "projects/test-project-123456/global/firewalls/firewall-create",
                      "service": "compute",
                      "type": "compute.firewalls",
                    },
                },
                {
                  "granted": true,
                  "permission": "compute.networks.updatePolicy",
                  "resourceAttributes":
                    {
                      "name": "projects/test-project-123456/global/networks/default",
                      "service": "compute",
                      "type": "compute.networks",
                    },
                },
              ],
            "methodName": "v1.compute.firewalls.patch",
            "request":
              {
                "@type": "type.googleapis.com/compute.firewalls.patch",
                "denieds": [{ "IPProtocol": "all" }],
              },
            "requestMetadata":
              {
                "callerIP": "12.12.12.12",
                "callerSuppliedUserAgent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/113.0.0.0 Safari/537.36,gzip(gfe),gzip(gfe)",
                "destinationAttributes": {},
                "requestAttributes":
                  {
                    "auth": {},
                    "reason": "8uSywAYQGg5Db2xpc2V1bSBGbG93cw",
                    "time": "2023-05-23T19:19:41.154751Z",
                  },
              },
            "resourceName": "projects/test-project-123456/global/firewalls/firewall-create",
            "response":
              {
                "@type": "type.googleapis.com/operation",
                "id": "896785227463044899",
                "insertTime": "2023-05-23T12:19:40.876-07:00",
                "name": "operation-1684869580331-5fc6144d418a9-e1332ca3-59c615ac",
                "operationType": "patch",
                "progress": "0",
                "selfLink": "https://www.googleapis.com/compute/v1/projects/test-project-123456/global/operations/operation-1684869580331-5fc6144d418a9-e1332ca3-59c615ac",
                "selfLinkWithId": "https://www.googleapis.com/compute/v1/projects/test-project-123456/global/operations/896785227463044899",
                "startTime": "2023-05-23T12:19:40.888-07:00",
                "status": "RUNNING",
                "targetId": "6563507997690081088",
                "targetLink": "https://www.googleapis.com/compute/v1/projects/test-project-123456/global/firewalls/firewall-create",
                "user": "user@domain.com",
              },
            "serviceName": "compute.googleapis.com",
          },
        "receivetimestamp": "2023-05-23 19:19:41.238",
        "resource":
          {
            "labels":
              {
                "firewall_rule_id": "6563507997690081088",
                "project_id": "test-project-123456",
              },
            "type": "gce_firewall_rule",
          },
        "severity": "NOTICE",
        "timestamp": "2023-05-23 19:19:40.353",
      }
  - Name: appengine.firewall.update-should-alert
    LogType: GCP.AuditLog
    ExpectedResult: true
    Log:
      {
        "insertid": "-xxxxxxxxxxxx",
        "logname": "projects/test-project-123456/logs/cloudaudit.googleapis.com%2Factivity",
        "protopayload":
          {
            "at_sign_type": "type.googleapis.com/google.cloud.audit.AuditLog",
            "authenticationInfo": { "principalEmail": "user@domain.com" },
            "authorizationInfo":
              [
                {
                  "granted": true,
                  "permission": "appengine.applications.update",
                  "resource": "apps/test-project-123456/firewall/ingressRules/1000",
                  "resourceAttributes": {},
                },
              ],
            "methodName": "google.appengine.v1.Firewall.UpdateIngressRule",
            "requestMetadata":
              {
                "callerIP": "12.12.12.12",
                "destinationAttributes": {},
                "requestAttributes":
                  { "auth": {}, "time": "2023-05-23T19:28:44.663413Z" },
              },
            "resourceName": "apps/test-project-123456/firewall/ingressRules/1000",
            "serviceData":
              {
                "@type": "type.googleapis.com/google.appengine.v1beta4.AuditData",
              },
            "serviceName": "appengine.googleapis.com",
            "status": {},
          },
        "receivetimestamp": "2023-05-23 19:28:45.473",
        "resource":
          {
            "labels":
              {
                "module_id": "",
                "project_id": "test-project-123456",
                "version_id": "",
                "zone": "",
              },
            "type": "gae_app",
          },
        "severity": "NOTICE",
        "timestamp": "2023-05-23 19:28:44.562",
      }
  - Name: compute.non-update.firewall.method-should-not-alert
    LogType: GCP.AuditLog
    ExpectedResult: false
    Log: { "methodName": "v1.compute.firewalls.insert" }
  - Name: appengine.compute.non-update.firewall.method-should-not-alert
    LogType: GCP.AuditLog
    ExpectedResult: false
    Log: { "methodName": "appengine.compute.v1.Firewall.PatchIngressRule" }
  - Name: randomservice.firewall-update.method-should-alert
    LogType: GCP.AuditLog
    ExpectedResult: true
    Log:
      {
        "protoPayload":
          {
            "authenticationInfo": { "principalEmail": "user@domain.com" },
            "methodName": "randomservice.compute.v1.Firewall.UpdateIngressRule",
            "resourceName": "randomservice/test-project-123456/firewall/ingressRules/1000",
            "requestMetadata":
              {
                "callerIP": "12.12.12.12",
                "destinationAttributes": {},
                "requestAttributes":
                  { "auth": {}, "time": "2023-05-23T19:28:44.663413Z" },
              },
          },
        "resource":
          {
            "labels":
              {
                "firewall_rule_id": "6563507997690081088",
                "project_id": "test-project-123456",
              },
            "type": "gce_firewall_rule",
          },
      }

Detection logic

Condition

protoPayload.methodName contains ".Firewall.Update" or protoPayload.methodName contains ".compute.firewalls.patch" or protoPayload.methodName contains ".compute.firewalls.update"

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`	contains	`.Firewall.Update` `.compute.firewalls.patch` `.compute.firewalls.update`

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
`project`	`resource.labels.project_id`
`principal`	`protoPayload.authenticationInfo.principalEmail`
`caller_ip`	`protoPayload.requestMetadata.callerIP`
`methodName`	`protoPayload.methodName`
`resourceName`	`protoPayload.resourceName`
`serviceName`	`protoPayload.serviceName`

`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)