GCP IAM serviceAccounts.signJwt Privilege Escalation

Severity: high
Log types: GCP.AuditLog
Reference: https://rhinosecuritylabs.com/gcp/privilege-escalation-google-cloud-platform-part-1/
Source: github.com/panther-labs/panther-analysis

Detects iam.serviceAccounts.signJwt method for privilege escalation in GCP. This method works by signing well-formed JSON web tokens (JWTs). The script for this method will sign a well-formed JWT and request a new access token belonging to the Service Account with it.

MITRE ATT&CK coverage

Tactic	Techniques
Privilege Escalation	`T1548` Abuse Elevation Control Mechanism

Rule body yaml

AnalysisType: rule
Filename: gcp_iam_serviceaccounts_signjwt.py
RuleID: "GCP.IAM.serviceAccounts.signJwt.Privilege.Escalation"
DisplayName: "GCP IAM serviceAccounts.signJwt Privilege Escalation"
Enabled: true
LogTypes:
  - GCP.AuditLog
Reports:
  MITRE ATT&CK:
    - TA0004:T1548
Severity: High
Description:
  Detects iam.serviceAccounts.signJwt method for privilege escalation in GCP. This method works
  by signing well-formed JSON web tokens (JWTs). The script for this method will sign a well-formed JWT and
  request a new access token belonging to the Service Account with it.
Runbook:
  These is not a vulnerability in GCP, this is a vulnerability in how you have configured your GCP environment,
  so it is your responsibility to be aware of these attack vectors and to defend against them. Make sure
  to follow the principle of least-privilege in your environments to help mitigate these security risks.
Reference: https://rhinosecuritylabs.com/gcp/privilege-escalation-google-cloud-platform-part-1/
Tests:
  - Name: JWT Signed
    ExpectedResult: true
    Log:
      {
        "protoPayload":
          {
            "@type": "type.googleapis.com/google.cloud.audit.AuditLog",
            "status": {},
            "authenticationInfo":
              {
                "principalEmail": "some-project@company.iam.gserviceaccount.com",
                "serviceAccountKeyName": "//iam.googleapis.com/projects/some-project/serviceAccounts/some-project@company.iam.gserviceaccount.com/keys/a378358365ff3d22e9c1a72fecf4605ddff76b47",
                "principalSubject": "serviceAccount:some-project@company.iam.gserviceaccount.com",
              },
            "requestMetadata":
              {
                "callerIp": "1.2.3.4",
                "requestAttributes":
                  { "time": "2024-02-26T17:15:16.327542536Z", "auth": {} },
                "destinationAttributes": {},
              },
            "serviceName": "iamcredentials.googleapis.com",
            "methodName": "SignJwt",
            "authorizationInfo":
              [
                {
                  "permission": "iam.serviceAccounts.signJwt",
                  "granted": true,
                  "resourceAttributes": {},
                },
              ],
            "resourceName": "projects/-/serviceAccounts/114885146936855121342",
            "request":
              {
                "name": "projects/-/serviceAccounts/some-project@company.iam.gserviceaccount.com",
                "@type": "type.googleapis.com/google.iam.credentials.v1.SignJwtRequest",
              },
          },
        "insertId": "1hu88qbef4d2o",
        "resource":
          {
            "type": "service_account",
            "labels":
              {
                "project_id": "some-project",
                "unique_id": "114885146936855121342",
                "email_id": "some-project@company.iam.gserviceaccount.com",
              },
          },
        "timestamp": "2024-02-26T17:15:16.314854637Z",
        "severity": "INFO",
        "logName": "projects/some-project/logs/cloudaudit.googleapis.com%2Fdata_access",
        "receiveTimestamp": "2024-02-26T17:15:17.100020459Z",
      }
  - Name: JWT Not Signed
    ExpectedResult: false
    Log:
      {
        "protoPayload":
          {
            "@type": "type.googleapis.com/google.cloud.audit.AuditLog",
            "status": {},
            "authenticationInfo":
              {
                "principalEmail": "some-project@company.iam.gserviceaccount.com",
                "serviceAccountKeyName": "//iam.googleapis.com/projects/some-project/serviceAccounts/some-project@company.iam.gserviceaccount.com/keys/a378358365ff3d22e9c1a72fecf4605ddff76b47",
                "principalSubject": "serviceAccount:some-project@company.iam.gserviceaccount.com",
              },
            "requestMetadata":
              {
                "callerIp": "1.2.3.4",
                "requestAttributes":
                  { "time": "2024-02-26T17:15:16.327542536Z", "auth": {} },
                "destinationAttributes": {},
              },
            "serviceName": "iamcredentials.googleapis.com",
            "methodName": "SignJwt",
            "authorizationInfo":
              [
                {
                  "permission": "iam.serviceAccounts.signJwt",
                  "granted": false,
                  "resourceAttributes": {},
                },
              ],
            "resourceName": "projects/-/serviceAccounts/114885146936855121342",
            "request":
              {
                "name": "projects/-/serviceAccounts/some-project@company.iam.gserviceaccount.com",
                "@type": "type.googleapis.com/google.iam.credentials.v1.SignJwtRequest",
              },
          },
        "insertId": "1hu88qbef4d2o",
        "resource":
          {
            "type": "service_account",
            "labels":
              {
                "project_id": "some-project",
                "unique_id": "114885146936855121342",
                "email_id": "some-project@company.iam.gserviceaccount.com",
              },
          },
        "timestamp": "2024-02-26T17:15:16.314854637Z",
        "severity": "INFO",
        "logName": "projects/some-project/logs/cloudaudit.googleapis.com%2Fdata_access",
        "receiveTimestamp": "2024-02-26T17:15:17.100020459Z",
      }

Detection logic

Condition

protoPayload.methodName eq "SignJwt"
protoPayload.authorizationInfo is_not_null
protoPayload.authorizationInfo array_any

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.authorizationInfo`	is_not_null	(no value, null check)
`protoPayload.methodName`	eq	`SignJwt`

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)