AWS WAF Managed Known Bad Inputs Passthrough Rule

Severity: high
Log types: AWS.WAFWebACL
Tags: AWS, WAF, Managed Rules, Initial Access:Exploit Public-Facing Application, Execution:Command and Scripting Interpreter
Reference: https://docs.aws.amazon.com/waf/latest/developerguide/aws-managed-rule-groups-baseline.html#aws-managed-rule-groups-baseline-known-bad-inputs
Source: github.com/panther-labs/panther-analysis

Detects AWS WAF Known Bad Inputs managed rule group matches. Covers Log4Shell (CVE-2021-44228), Java deserialization RCE, localhost Host header abuse, PROPFIND method, and exploitable paths.

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1190` Exploit Public-Facing Application
Execution	`T1059` Command and Scripting Interpreter

Rule body yaml

AnalysisType: rule
Filename: aws_waf_managed_known_bad_inputs.py
RuleID: "AWS.WAF.Managed.KnownBadInputs"
DisplayName: "AWS WAF Managed Known Bad Inputs Passthrough Rule"
Enabled: true
LogTypes:
  - AWS.WAFWebACL
Tags:
  - AWS
  - WAF
  - Managed Rules
  - Initial Access:Exploit Public-Facing Application
  - Execution:Command and Scripting Interpreter
Reports:
  MITRE ATT&CK:
    - TA0001:T1190
    - TA0002:T1059
Severity: High
Description: >
  Detects AWS WAF Known Bad Inputs managed rule group matches. Covers Log4Shell (CVE-2021-44228),
  Java deserialization RCE, localhost Host header abuse, PROPFIND method, and exploitable paths.
Runbook: |
  1. Find all WAF log entries from httpRequest:clientIp in the 6 hours before and after this alert to identify exploitation attempts across multiple endpoints
  2. Check if httpRequest:clientIp appears in threat intelligence feeds or is associated with known exploit infrastructure
  3. If the action was ALLOW, search application and backend server logs for the targeted httpRequest:uri in the 1 hour after the alert to determine if exploitation was successful
Reference: https://docs.aws.amazon.com/waf/latest/developerguide/aws-managed-rule-groups-baseline.html#aws-managed-rule-groups-baseline-known-bad-inputs
Tests:
  - Name: Log4Shell 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-AWSManagedRulesKnownBadInputsRuleSet"
      terminatingRuleType: "MANAGED_RULE_GROUP"
      action: "BLOCK"
      httpSourceName: "ALB"
      httpRequest:
        clientIp: "203.0.113.45"
        country: "US"
        uri: "/api/endpoint"
        httpMethod: "POST"

  - Name: Java deserialization in ruleGroupList
    ExpectedResult: true
    Log:
      timestamp: "2024-03-20T10:35:00.000Z"
      webaclId: "arn:aws:wafv2:us-east-1:123456789012:regional/webacl/test/a1b2c3d4"
      terminatingRuleId: "AWS-AWSManagedRulesKnownBadInputsRuleSet"
      action: "BLOCK"
      httpSourceName: "ALB"
      httpRequest:
        clientIp: "198.51.100.22"
        country: "CN"
        uri: "/api/v1/process"
        httpMethod: "POST"
      ruleGroupList:
        - ruleGroupId: "AWS#AWSManagedRulesKnownBadInputsRuleSet"
          terminatingRule:
            ruleId: "JavaDeserializationRCE_BODY"
            action: "BLOCK"

  - Name: Non-terminating Log4Shell match (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: "/login"
        httpMethod: "POST"
      ruleGroupList:
        - ruleGroupId: "AWS#AWSManagedRulesKnownBadInputsRuleSet"
          nonTerminatingMatchingRules:
            - ruleId: "Log4JRCE_BODY"
              action: "COUNT"

  - Name: Exploitable path via API Gateway
    ExpectedResult: true
    Log:
      timestamp: "2024-03-20T10:45:00.000Z"
      webaclId: "arn:aws:wafv2:us-east-1:123456789012:regional/webacl/test/a1b2c3d4"
      terminatingRuleId: "AWS-AWSManagedRulesKnownBadInputsRuleSet"
      action: "BLOCK"
      httpSourceName: "APIGW"
      httpRequest:
        clientIp: "203.0.113.45"
        uri: "/.env"
        httpMethod: "GET"
      ruleGroupList:
        - ruleGroupId: "AWS#AWSManagedRulesKnownBadInputsRuleSet"
          terminatingRule:
            ruleId: "ExploitablePaths_URIPATH"
            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-AWSManagedRulesCommonRuleSet"
      action: "BLOCK"
      httpSourceName: "ALB"
      httpRequest:
        clientIp: "203.0.113.45"

  - 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)