Lambda Code Updated by User

Status: Experimental
Severity: high
Log types: AWS.CloudTrail
Reference: https://stratus-red-team.cloud/attack-techniques/AWS/aws.persistence.lambda-overwrite-code/
Source: github.com/panther-labs/panther-analysis

Detects when Lambda function code is updated by an IAM user, federated user, or AWS SSO user. This may indicate compromised credentials, a developer bypassing CI/CD guardrails, or insider threat activity.

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1078` Valid Accounts
Persistence	`T1078` Valid Accounts
Privilege Escalation	`T1078` Valid Accounts
Stealth	`T1078` Valid Accounts

Rules detecting the same action

Other rules on this platform that filter on the same API call or operation.

AWS Discovery API Calls via CLI from a Single Resource (Elastic)
AWS Lambda Function Created or Updated (Elastic)
AWS Lambda Function Policy Updated to Allow Public Invocation (Elastic)
AWS Lambda Layer Added to Existing Function (Elastic)
AWS New Lambda Layer Attached (Sigma)

Rule body yaml

AnalysisType: rule
Filename: aws_overwrite_lambda_code.py
RuleID: "AWS.Lambda.UpdateFunctionCode"
DisplayName: "Lambda Code Updated by User"
Enabled: true
CreateAlert: true
LogTypes:
  - AWS.CloudTrail
Reports:
  MITRE ATT&CK:
    - TA0007:T1078
Severity: High
Status: Experimental
Description: >
  Detects when Lambda function code is updated by an IAM user, federated user, or AWS SSO user.
  This may indicate compromised credentials, a developer bypassing CI/CD guardrails,
  or insider threat activity.
Runbook: |
  Verify the user identity and whether this is authorized.
  Review the code changes made to the Lambda function.
  If unauthorized:
  - Disable the user's access key or revoke the SSO session
  - Revert Lambda function code to previous version
  - Investigate credential compromise
Reference: https://stratus-red-team.cloud/attack-techniques/AWS/aws.persistence.lambda-overwrite-code/
Tests:
  - Name: IAM User Updates Lambda Code
    ExpectedResult: true
    Log:
      {
        "eventVersion": "1.05",
        "userIdentity": {
          "type": "IAMUser",
          "principalId": "AIDAI123456789EXAMPLE",
          "arn": "arn:aws:iam::123456789012:user/john.developer",
          "accountId": "123456789012",
          "accessKeyId": "AKIAI123456789EXAMPLE",
          "userName": "john.developer"
        },
        "eventTime": "2019-01-01T00:00:00Z",
        "eventSource": "lambda.amazonaws.com",
        "eventName": "UpdateFunctionCode20150331v2",
        "awsRegion": "us-west-2",
        "sourceIPAddress": "203.0.113.50",
        "userAgent": "aws-cli/2.13.5 Python/3.11.4",
        "requestParameters": {
          "functionName": "production-api"
        },
        "responseElements": {
          "functionName": "production-api"
        },
        "requestID": "1",
        "eventID": "1",
        "readOnly": false,
        "eventType": "AwsApiCall",
        "recipientAccountId": "123456789012",
        "p_log_type": "AWS.CloudTrail"
      }
  - Name: AssumedRole Updates Lambda Code (Normal CI/CD)
    ExpectedResult: false
    Log:
      {
        "eventVersion": "1.05",
        "userIdentity": {
          "type": "AssumedRole",
          "principalId": "tester",
          "arn": "arn:aws:sts::123456789012:assumed-role/tester",
          "accountId": "123456789012",
          "accessKeyId": "1",
          "sessionContext": {
            "sessionIssuer": {
              "type": "Role",
              "principalId": "1111",
              "arn": "arn:aws:iam::123456789012:role/tester",
              "accountId": "123456789012",
              "userName": "Tester"
            },
            "webIdFederationData": {},
            "attributes": {
              "mfaAuthenticated": "true",
              "creationDate": "2019-01-01T00:00:00Z"
            }
          }
        },
        "eventTime": "2019-01-01T00:00:00Z",
        "eventSource": "lambda.amazonaws.com",
        "eventName": "UpdateFunctionCode20150331",
        "awsRegion": "us-west-2",
        "sourceIPAddress": "111.111.111.111",
        "userAgent": "console.amazonaws.com",
        "requestParameters": {
          "functionName": "my-lambda-function"
        },
        "responseElements": {
          "functionName": "my-lambda-function"
        },
        "requestID": "1",
        "eventID": "1",
        "readOnly": false,
        "eventType": "AwsApiCall",
        "recipientAccountId": "123456789012",
        "p_log_type": "AWS.CloudTrail"
      }
  - Name: SSO AssumedRole Updates Lambda Code
    ExpectedResult: true
    Log:
      {
        "eventVersion": "1.05",
        "userIdentity": {
          "type": "AssumedRole",
          "principalId": "AROA123456789EXAMPLE:bob.ross",
          "arn": "arn:aws:sts::123456789012:assumed-role/AWSReservedSSO_DevAdmin_abc123/bob.ross",
          "accountId": "123456789012",
          "accessKeyId": "ASIA123456789EXAMPLE",
          "sessionContext": {
            "sessionIssuer": {
              "type": "Role",
              "principalId": "AROA123456789EXAMPLE",
              "arn": "arn:aws:iam::123456789012:role/aws-reserved/sso.amazonaws.com/AWSReservedSSO_DevAdmin_abc123",
              "accountId": "123456789012",
              "userName": "AWSReservedSSO_DevAdmin_abc123"
            },
            "webIdFederationData": {},
            "attributes": {
              "mfaAuthenticated": "false",
              "creationDate": "2019-01-01T00:00:00Z"
            }
          }
        },
        "eventTime": "2019-01-01T00:00:00Z",
        "eventSource": "lambda.amazonaws.com",
        "eventName": "UpdateFunctionCode20150331v2",
        "awsRegion": "us-west-2",
        "sourceIPAddress": "203.0.113.50",
        "userAgent": "aws-cli/2.13.5 Python/3.11.4",
        "requestParameters": {
          "functionName": "production-api"
        },
        "responseElements": {
          "functionName": "production-api"
        },
        "requestID": "1",
        "eventID": "1",
        "readOnly": false,
        "eventType": "AwsApiCall",
        "recipientAccountId": "123456789012",
        "p_log_type": "AWS.CloudTrail"
      }
  - Name: FederatedUser Updates Lambda Code
    ExpectedResult: true
    Log:
      {
        "eventVersion": "1.05",
        "userIdentity": {
          "type": "FederatedUser",
          "principalId": "123456789012:federated-user",
          "arn": "arn:aws:sts::123456789012:federated-user/federated-user",
          "accountId": "123456789012",
          "accessKeyId": "ASIA123456789EXAMPLE"
        },
        "eventTime": "2019-01-01T00:00:00Z",
        "eventSource": "lambda.amazonaws.com",
        "eventName": "UpdateFunctionCode20150331v2",
        "awsRegion": "us-west-2",
        "sourceIPAddress": "203.0.113.50",
        "userAgent": "aws-cli/2.13.5 Python/3.11.4",
        "requestParameters": {
          "functionName": "production-api"
        },
        "responseElements": {
          "functionName": "production-api"
        },
        "requestID": "1",
        "eventID": "1",
        "readOnly": false,
        "eventType": "AwsApiCall",
        "recipientAccountId": "123456789012",
        "p_log_type": "AWS.CloudTrail"
      }
  - Name: AssumedRole Updates Lambda Code v2 (Normal CI/CD)
    ExpectedResult: false
    Log:
      {
        "eventVersion": "1.05",
        "userIdentity": {
          "type": "AssumedRole",
          "principalId": "tester",
          "arn": "arn:aws:sts::123456789012:assumed-role/tester",
          "accountId": "123456789012",
          "accessKeyId": "1",
          "sessionContext": {
            "sessionIssuer": {
              "type": "Role",
              "principalId": "1111",
              "arn": "arn:aws:iam::123456789012:role/tester",
              "accountId": "123456789012",
              "userName": "Tester"
            },
            "webIdFederationData": {},
            "attributes": {
              "mfaAuthenticated": "true",
              "creationDate": "2019-01-01T00:00:00Z"
            }
          }
        },
        "eventTime": "2019-01-01T00:00:00Z",
        "eventSource": "lambda.amazonaws.com",
        "eventName": "UpdateFunctionCode20150331v2",
        "awsRegion": "us-west-2",
        "sourceIPAddress": "111.111.111.111",
        "userAgent": "console.amazonaws.com",
        "requestParameters": {
          "functionName": "my-lambda-function"
        },
        "responseElements": {
          "functionName": "my-lambda-function"
        },
        "requestID": "1",
        "eventID": "1",
        "readOnly": false,
        "eventType": "AwsApiCall",
        "recipientAccountId": "123456789012",
        "p_log_type": "AWS.CloudTrail"
      }
  - Name: Delete Function Event
    ExpectedResult: false
    Log:
      {
        "eventVersion": "1.05",
        "userIdentity": {
          "type": "AssumedRole",
          "principalId": "tester",
          "arn": "arn:aws:sts::123456789012:assumed-role/tester",
          "accountId": "123456789012",
          "accessKeyId": "1",
          "sessionContext": {
            "sessionIssuer": {
              "type": "Role",
              "principalId": "1111",
              "arn": "arn:aws:iam::123456789012:role/tester",
              "accountId": "123456789012",
              "userName": "Tester"
            },
            "webIdFederationData": {},
            "attributes": {
              "mfaAuthenticated": "true",
              "creationDate": "2019-01-01T00:00:00Z"
            }
          }
        },
        "eventTime": "2019-01-01T00:00:00Z",
        "eventSource": "lambda.amazonaws.com",
        "eventName": "DeleteFunction",
        "awsRegion": "us-west-2",
        "sourceIPAddress": "111.111.111.111",
        "userAgent": "console.amazonaws.com",
        "requestParameters": {
          "functionName": "my-lambda-function"
        },
        "responseElements": {
          "functionName": "my-lambda-function"
        },
        "requestID": "1",
        "eventID": "1",
        "readOnly": false,
        "eventType": "AwsApiCall",
        "recipientAccountId": "123456789012",
        "p_log_type": "AWS.CloudTrail"
      }

Detection logic

Condition

not (errorCode is_not_null or errorMessage is_not_null)
eventSource eq "lambda.amazonaws.com"
eventName starts_with "UpdateFunctionCode"
userIdentity.type in ["IAMUser", "FederatedUser"] or (userIdentity.type eq "AssumedRole" and userIdentity.sessionContext.sessionIssuer.userName starts_with "AWSReservedSSO_")

Exclusions

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

Field	Kind	Excluded values
`errorCode`	is_not_null	(no value, null check)
`errorMessage`	is_not_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
`eventName`	starts_with	`UpdateFunctionCode`
`eventSource`	eq	`lambda.amazonaws.com`
`userIdentity.sessionContext.sessionIssuer.userName`	starts_with	`AWSReservedSSO_`
`userIdentity.type`	eq	`AssumedRole`
`userIdentity.type`	in	`FederatedUser` `IAMUser`

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
`eventName`
`eventSource`
`awsRegion`
`recipientAccountId`
`sourceIPAddress`
`userAgent`
`userIdentity`
`actor_user`
`functionName`	`responseElements.functionName`

`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)