DNS Base64 Encoded Query

Severity: medium
Entities: domain_names, ip_addresses, md5_hashes, trace_ids
Log types: Crowdstrike.FDREvent, AWS.VPCDns, CiscoUmbrella.DNS
Reference: https://zofixer.com/what-is-base64-disclosure-vulnerability/
Source: github.com/panther-labs/panther-analysis

Detects DNS queries with Base64 encoded subdomains, which could indicate an attempt to obfuscate data exfil.

Rule body yaml

AnalysisType: rule
DisplayName: "DNS Base64 Encoded Query"
Description: Detects DNS queries with Base64 encoded subdomains, which could indicate an attempt to obfuscate data exfil.
RuleID: "Standard.DNSBase64"
Enabled: false
Filename: standard_dns_base64.py
Reference: https://zofixer.com/what-is-base64-disclosure-vulnerability/
Severity: Medium
DedupPeriodMinutes: 60
Threshold: 1
LogTypes:
  - Crowdstrike.FDREvent
  - AWS.VPCDns
  - CiscoUmbrella.DNS
Tests:
  - Name: AWS VPC DNS (Positive)
    ExpectedResult: true
    Log:
      {
        "account_id": "123456789012",
        "answers": [{ "Class": "IN", "Rdata": "172.31.46.187", "Type": "A" }],
        "p_log_type": "AWS.VPCDns",
        "query_class": "IN",
        "query_name": "c29tZSBsb25nIGJhc2U2NCBzdHJpbmc=.file1.16s.us",
        "query_timestamp": "2023-04-11 01:29:20",
        "query_type": "A",
        "rcode": "NOERROR",
        "region": "us-west-2",
        "srcaddr": "172.31.46.187",
        "srcids": { "instance": "i-09d9aa4e31675db61" },
        "srcport": "36899",
        "transport": "UDP",
        "version": "1.100000",
        "vpc_id": "vpc-c26c48ba",
      }
  - Name: AWS VPS DNS (Negative)
    ExpectedResult: false
    Log:
      {
        "account_id": "123456789012",
        "answers": [{ "Class": "IN", "Rdata": "172.31.46.187", "Type": "A" }],
        "p_log_type": "AWS.VPCDns",
        "query_class": "IN",
        "query_name": "test.com",
        "query_timestamp": "2023-04-11 01:29:20",
        "query_type": "A",
        "rcode": "NOERROR",
        "region": "us-west-2",
        "srcaddr": "172.31.46.187",
        "srcids": { "instance": "i-09d9aa4e31675db61" },
        "srcport": "36899",
        "transport": "UDP",
        "version": "1.100000",
        "vpc_id": "vpc-c26c48ba",
      }
  - Name: AWS VPS DNS subdomain (Negative)
    ExpectedResult: false
    Log:
      {
        "account_id": "123456789012",
        "answers": [{ "Class": "IN", "Rdata": "172.31.46.187", "Type": "A" }],
        "p_log_type": "AWS.VPCDns",
        "query_class": "IN",
        "query_name": "=.test.com",
        "query_timestamp": "2023-04-11 01:29:20",
        "query_type": "A",
        "rcode": "NOERROR",
        "region": "us-west-2",
        "srcaddr": "172.31.46.187",
        "srcids": { "instance": "i-09d9aa4e31675db61" },
        "srcport": "36899",
        "transport": "UDP",
        "version": "1.100000",
        "vpc_id": "vpc-c26c48ba",
      }
  - Name: Crowdstrike DNS Request (Positive)
    ExpectedResult: true
    Log:
      {
        "ConfigBuild": "1007.3.0016606.11",
        "ConfigStateHash": "1331552299",
        "ContextProcessId": "21866918",
        "ContextThreadId": "43270698197",
        "ContextTimeStamp": "2023-04-23 18:50:03.172",
        "Entitlements": "15",
        "aid": "877761efa8db44d792ddc2redacted",
        "aip": "1.1.1.1",
        "cid": "cfe698690964434083fecdredacted",
        "event":
          {
            "ConfigBuild": "1007.3.0016606.11",
            "ConfigStateHash": "1331552299",
            "ContextProcessId": "21866918",
            "ContextThreadId": "43270698197",
            "ContextTimeStamp": "1682275803.172",
            "DnsRequestCount": "1",
            "DomainName": "VGhpcyBpcyBhIHN1c3BpY2lvdXMgZGF0YSBleGZpbHRyYXRpb24gY2h1bms=.example.com.",
            "DualRequest": "0",
            "EffectiveTransmissionClass": "3",
            "Entitlements": "15",
            "EventOrigin": "1",
            "InterfaceIndex": "0",
            "QueryStatus": "9003",
            "RequestType": "1",
            "aid": "877761efa8db44d792ddc2redacted",
            "aip": "1.1.1.1",
            "cid": "cfe698690964434083fecdredacted",
            "event_platform": "Win",
            "event_simpleName": "DnsRequest",
            "id": "4f006a14-0fdf-474e-bfca-021a00a935ad",
            "name": "DnsRequestV4",
            "timestamp": "1682275805712",
          },
        "event_platform": "Win",
        "event_simpleName": "DnsRequest",
        "fdr_event_type": "DnsRequest",
        "id": "4f006a14-0fdf-474e-bfca-021a00a935ad",
        "name": "DnsRequestV4",
        "p_any_domain_names": ["win8.ipv6.microsoft.com"],
        "p_any_ip_addresses": ["1.1.1.1"],
        "p_any_md5_hashes":
          ["877761efa8db44d792ddc2redacted", "cfe698690964434083fecdredacted"],
        "p_any_trace_ids":
          ["877761efa8db44d792ddc2redacted", "cfe698690964434083fecdredacted"],
        "p_event_time": "2023-04-23 18:50:03.172",
        "p_log_type": "Crowdstrike.FDREvent",
        "p_parse_time": "2023-04-23 19:00:53.11",
        "p_row_id": "f2c89ec8f09cbc8ca2c1cbdf171a",
        "p_schema_version": 0,
        "p_source_id": "1f33f64c-124d-413c-a9e3-d51ccedd8e77",
        "p_source_label": "Crowdstrike-FDR-Dev",
        "timestamp": "2023-04-23 18:50:05.712",
      }
  - Name: Crowdstrike DNS Request (Negative)
    ExpectedResult: false
    Log:
      {
        "ConfigBuild": "1007.3.0016606.11",
        "ConfigStateHash": "1331552299",
        "ContextProcessId": "21866918",
        "ContextThreadId": "43270698197",
        "ContextTimeStamp": "2023-04-23 18:50:03.172",
        "Entitlements": "15",
        "aid": "877761efa8db44d792ddc2redacted",
        "aip": "1.1.1.1",
        "cid": "cfe698690964434083fecdredacted",
        "event":
          {
            "ConfigBuild": "1007.3.0016606.11",
            "ConfigStateHash": "1331552299",
            "ContextProcessId": "21866918",
            "ContextThreadId": "43270698197",
            "ContextTimeStamp": "1682275803.172",
            "DnsRequestCount": "1",
            "DomainName": "win8.ipv6.microsoft.com.",
            "DualRequest": "0",
            "EffectiveTransmissionClass": "3",
            "Entitlements": "15",
            "EventOrigin": "1",
            "InterfaceIndex": "0",
            "QueryStatus": "9003",
            "RequestType": "1",
            "aid": "877761efa8db44d792ddc2redacted",
            "aip": "1.1.1.1",
            "cid": "cfe698690964434083fecdredacted",
            "event_platform": "Win",
            "event_simpleName": "DnsRequest",
            "id": "4f006a14-0fdf-474e-bfca-021a00a935ad",
            "name": "DnsRequestV4",
            "timestamp": "1682275805712",
          },
        "event_platform": "Win",
        "event_simpleName": "DnsRequest",
        "fdr_event_type": "DnsRequest",
        "id": "4f006a14-0fdf-474e-bfca-021a00a935ad",
        "name": "DnsRequestV4",
        "p_any_domain_names": ["win8.ipv6.microsoft.com"],
        "p_any_ip_addresses": ["1.1.1.1"],
        "p_any_md5_hashes":
          ["877761efa8db44d792ddc2redacted", "cfe698690964434083fecdredacted"],
        "p_any_trace_ids":
          ["877761efa8db44d792ddc2redacted", "cfe698690964434083fecdredacted"],
        "p_event_time": "2023-04-23 18:50:03.172",
        "p_log_type": "Crowdstrike.FDREvent",
        "p_parse_time": "2023-04-23 19:00:53.11",
        "p_row_id": "f2c89ec8f09cbc8ca2c1cbdf171a",
        "p_schema_version": 0,
        "p_source_id": "1f33f64c-124d-413c-a9e3-d51ccedd8e77",
        "p_source_label": "Crowdstrike-FDR-Dev",
        "timestamp": "2023-04-23 18:50:05.712",
      }
  - Name: Cisco Umbrella DNS Request (Positive)
    ExpectedResult: true
    Log:
      {
        "action": "Allow",
        "internalIp": "136.24.229.58",
        "externalIp": "136.24.229.58",
        "timestamp": "2020-05-21 19:20:25.000",
        "responseCode": "NOERROR",
        "domain": "c29tZSBsb25nIGJhc2U2NCBzdHJpbmc=.example.io.",
        "p_log_type": "CiscoUmbrella.DNS",
      }
  - Name: Cisco Umbrella DNS Request (Negative)
    ExpectedResult: false
    Log:
      {
        "action": "Allow",
        "internalIp": "136.24.229.58",
        "externalIp": "136.24.229.58",
        "timestamp": "2020-05-21 19:20:25.000",
        "responseCode": "NOERROR",
        "domain": "c29tZSBsb25IGJhc2.example.io.",
        "p_log_type": "CiscoUmbrella.DNS",
      }
  - Name: Crowdstrike no query
    ExpectedResult: false
    Log:
      {
        "ConfigBuild": "1007.3.0016606.11",
        "ConfigStateHash": "1331552299",
        "ContextProcessId": "21866918",
        "ContextThreadId": "43270698197",
        "ContextTimeStamp": "2023-04-23 18:50:03.172",
        "Entitlements": "15",
        "aid": "877761efa8db44d792ddc2redacted",
        "aip": "1.1.1.1",
        "cid": "cfe698690964434083fecdredacted",
        "event":
          {
            "ConfigBuild": "1007.3.0016606.11",
            "ConfigStateHash": "1331552299",
            "ContextProcessId": "21866918",
            "ContextThreadId": "43270698197",
            "ContextTimeStamp": "1682275803.172",
            "DnsRequestCount": "1",
            "DualRequest": "0",
            "EffectiveTransmissionClass": "3",
            "Entitlements": "15",
            "EventOrigin": "1",
            "InterfaceIndex": "0",
            "QueryStatus": "9003",
            "RequestType": "1",
            "aid": "877761efa8db44d792ddc2redacted",
            "aip": "1.1.1.1",
            "cid": "cfe698690964434083fecdredacted",
            "event_platform": "Win",
            "event_simpleName": "DnsRequest",
            "id": "4f006a14-0fdf-474e-bfca-021a00a935ad",
            "name": "DnsRequestV4",
            "timestamp": "1682275805712",
          },
        "event_platform": "Win",
        "event_simpleName": "DnsRequest",
        "fdr_event_type": "DnsRequest",
        "id": "4f006a14-0fdf-474e-bfca-021a00a935ad",
        "name": "DnsRequestV4",
        "p_any_domain_names": ["win8.ipv6.microsoft.com"],
        "p_any_ip_addresses": ["1.1.1.1"],
        "p_any_md5_hashes":
          ["877761efa8db44d792ddc2redacted", "cfe698690964434083fecdredacted"],
        "p_any_trace_ids":
          ["877761efa8db44d792ddc2redacted", "cfe698690964434083fecdredacted"],
        "p_event_time": "2023-04-23 18:50:03.172",
        "p_log_type": "Crowdstrike.FDREvent",
        "p_parse_time": "2023-04-23 19:00:53.11",
        "p_row_id": "f2c89ec8f09cbc8ca2c1cbdf171a",
        "p_schema_version": 0,
        "p_source_id": "1f33f64c-124d-413c-a9e3-d51ccedd8e77",
        "p_source_label": "Crowdstrike-FDR-Dev",
        "timestamp": "2023-04-23 18:50:05.712",
      }
  - Name: Crowdstrike 32-char service ID (Negative)
    ExpectedResult: false
    Log:
      {
        "aid": "d825772fcca046f3b2876decaafacd60",
        "aip": "83.106.110.25",
        "cid": "e4a46c2a445744f7860dcf62bf1b6ad4",
        "event":
          {
            "DomainName": "4ifgvg5jcq6meu7m4acon5vnfa0kocom.cloudfront.net.",
            "event_platform": "Win",
            "event_simpleName": "DnsRequest",
          },
        "event_platform": "Win",
        "event_simpleName": "DnsRequest",
        "fdr_event_type": "DnsRequest",
        "p_log_type": "Crowdstrike.FDREvent",
      }
  - Name: AWS VPC DNS - label decodes to CJK (Negative - isascii fix)
    ExpectedResult: false
    Log:
      {
        "account_id": "123456789012",
        "p_log_type": "AWS.VPCDns",
        "query_class": "IN",
        "query_name": "c2VydmljZXPkuK1pZGVudGlmaWVy.serviceregistry.internal",
        "query_timestamp": "2024-01-01 00:00:00",
        "query_type": "A",
        "rcode": "NOERROR",
        "region": "us-east-1",
        "srcaddr": "10.0.0.1",
        "version": "1.000000",
        "vpc_id": "vpc-12345678",
      }
  - Name: AWS VPC DNS - label decodes to pure ASCII exfil data (Positive)
    ExpectedResult: true
    Log:
      {
        "account_id": "123456789012",
        "p_log_type": "AWS.VPCDns",
        "query_class": "IN",
        "query_name": "c2VjcmV0LWRhdGEtZXhmaWwtY2h1bms.malicious.com",
        "query_timestamp": "2024-01-01 00:00:00",
        "query_type": "A",
        "rcode": "NOERROR",
        "region": "us-east-1",
        "srcaddr": "10.0.0.1",
        "version": "1.000000",
        "vpc_id": "vpc-12345678",
      }

Detection logic

Condition

dns_query is_not_null

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

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
`dns_query`	is_not_null	(no value, null check)

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_ip`

`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)