AWS WAF Managed Core Rule Set Passthrough Rule

Severity: medium
Log types: AWS.WAFWebACL
Tags: AWS, WAF, Managed Rules, Initial Access:Exploit Public-Facing Application
Reference: https://docs.aws.amazon.com/waf/latest/developerguide/aws-managed-rule-groups-baseline.html#aws-managed-rule-groups-baseline-crs
Source: github.com/panther-labs/panther-analysis

Detects AWS WAF Core Rule Set (CRS) managed rule group matches. Covers XSS, LFI, RFI, SSRF, size restrictions, restricted extensions, and bad bot user agents across all WAF sources.

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1190` Exploit Public-Facing Application

Rule body yaml

AnalysisType: rule
Filename: aws_waf_managed_core_rule_set.py
RuleID: "AWS.WAF.Managed.CoreRuleSet"
DisplayName: "AWS WAF Managed Core Rule Set Passthrough Rule"
Enabled: true
LogTypes:
  - AWS.WAFWebACL
Tags:
  - AWS
  - WAF
  - Managed Rules
  - Initial Access:Exploit Public-Facing Application
Reports:
  MITRE ATT&CK:
    - TA0001:T1190
Severity: Medium
Description: >
  Detects AWS WAF Core Rule Set (CRS) managed rule group matches. Covers XSS, LFI, RFI, SSRF,
  size restrictions, restricted extensions, and bad bot user agents across all WAF sources.
Runbook: |
  1. Find all WAF log entries from httpRequest:clientIp in the 6 hours before and after this alert to identify attack patterns or scanning behavior
  2. Check if httpRequest:clientIp appears in threat intelligence feeds or is associated with known proxy/VPN services
  3. Search for other WAF alerts targeting the same httpRequest:uri or httpSourceId in the past 7 days to determine if this is part of a broader campaign
Reference: https://docs.aws.amazon.com/waf/latest/developerguide/aws-managed-rule-groups-baseline.html#aws-managed-rule-groups-baseline-crs
Tests:
  - Name: Blocked via terminatingRuleId
    ExpectedResult: true
    Log:
      timestamp: "2024-03-20T10:30:00.000Z"
      webaclId: "arn:aws:wafv2:us-east-1:123456789012:regional/webacl/test/a1b2c3d4"
      terminatingRuleId: "AWS-AWSManagedRulesCommonRuleSet"
      terminatingRuleType: "MANAGED_RULE_GROUP"
      action: "BLOCK"
      httpSourceName: "ALB"
      httpRequest:
        clientIp: "203.0.113.45"
        country: "US"
        uri: "/api/endpoint"
        httpMethod: "POST"

  - Name: Match in ruleGroupList terminating rule
    ExpectedResult: true
    Log:
      timestamp: "2024-03-20T10:35:00.000Z"
      webaclId: "arn:aws:wafv2:us-east-1:123456789012:regional/webacl/test/a1b2c3d4"
      terminatingRuleId: "AWS-AWSManagedRulesCommonRuleSet"
      action: "BLOCK"
      httpSourceName: "ALB"
      httpRequest:
        clientIp: "198.51.100.22"
        country: "CN"
        uri: "/etc/passwd"
        httpMethod: "GET"
      ruleGroupList:
        - ruleGroupId: "AWS#AWSManagedRulesCommonRuleSet"
          terminatingRule:
            ruleId: "GenericLFI_URIPATH"
            action: "BLOCK"

  - Name: Non-terminating match in rule group (COUNT mode)
    ExpectedResult: true
    Log:
      timestamp: "2024-03-20T10:40:00.000Z"
      webaclId: "arn:aws:wafv2:us-east-1:123456789012:regional/webacl/test/a1b2c3d4"
      terminatingRuleId: "Default_Action"
      action: "ALLOW"
      httpSourceName: "CF"
      httpRequest:
        clientIp: "192.0.2.100"
        country: "RU"
        uri: "/search?q=<script>alert(1)</script>"
        httpMethod: "GET"
      ruleGroupList:
        - ruleGroupId: "AWS#AWSManagedRulesCommonRuleSet"
          nonTerminatingMatchingRules:
            - ruleId: "CrossSiteScripting_QUERYARGUMENTS"
              action: "COUNT"

  - Name: CloudFront SSRF detection
    ExpectedResult: true
    Log:
      timestamp: "2024-03-20T10:45:00.000Z"
      webaclId: "arn:aws:wafv2:us-east-1:123456789012:regional/webacl/test/a1b2c3d4"
      terminatingRuleId: "AWS-AWSManagedRulesCommonRuleSet"
      action: "BLOCK"
      httpSourceName: "CF"
      httpRequest:
        clientIp: "203.0.113.45"
        uri: "/proxy?url=http://169.254.169.254/latest/meta-data/"
        httpMethod: "GET"
      ruleGroupList:
        - ruleGroupId: "AWS#AWSManagedRulesCommonRuleSet"
          terminatingRule:
            ruleId: "EC2MetaDataSSRF_QUERYARGUMENTS"
            action: "BLOCK"

  - Name: Different rule group - no alert
    ExpectedResult: false
    Log:
      timestamp: "2024-03-20T10:50:00.000Z"
      webaclId: "arn:aws:wafv2:us-east-1:123456789012:regional/webacl/test/a1b2c3d4"
      terminatingRuleId: "AWS-AWSManagedRulesKnownBadInputsRuleSet"
      action: "BLOCK"
      httpSourceName: "ALB"
      httpRequest:
        clientIp: "203.0.113.45"
      ruleGroupList:
        - ruleGroupId: "AWS#AWSManagedRulesKnownBadInputsRuleSet"
          terminatingRule:
            ruleId: "Log4JRCE_BODY"
            action: "BLOCK"

  - Name: Normal traffic - no alert
    ExpectedResult: false
    Log:
      timestamp: "2024-03-20T10:55:00.000Z"
      webaclId: "arn:aws:wafv2:us-east-1:123456789012:regional/webacl/test/a1b2c3d4"
      terminatingRuleId: "Default_Action"
      action: "ALLOW"
      httpSourceName: "ALB"
      httpRequest:
        clientIp: "198.51.100.10"

DedupPeriodMinutes: 60
Threshold: 1

Detection logic

Condition

nonTerminatingMatchingRules array_any or ruleGroupList array_any

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

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
`matched_rule`	`terminatingRuleId`
`client_ip`	`httpRequest.clientIp`
`country`	`httpRequest.country`
`http_method`	`httpRequest.httpMethod`
`uri`	`httpRequest.uri`
`action`
`source`	`httpSourceName`
`source_id`	`httpSourceId`
`terminating_rule_id`	`terminatingRuleId`
`terminating_rule_type`	`terminatingRuleType`

`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)