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Detection rules › Sigma

Attempts of Kerberos Coercion Via DNS SPN Spoofing

Status
experimental
Severity
high
Log source
product windows, category process_creation
Author
Swachchhanda Shrawan Poudel (Nextron Systems)
Source
github.com/SigmaHQ/sigma

Detects the presence of "UWhRC....AAYBAAAA" pattern in command line. The pattern "1UWhRCAAAAA..BAAAA" is a base64-encoded signature that corresponds to a marshaled CREDENTIAL_TARGET_INFORMATION structure. Attackers can use this technique to coerce authentication from victim systems to attacker-controlled hosts. It is one of the strong indicators of a Kerberos coercion attack, where adversaries manipulate DNS records to spoof Service Principal Names (SPNs) and redirect authentication requests like in CVE-2025-33073. If you see this pattern in the command line, it is likely an attempt to add spoofed Service Principal Names (SPNs) to DNS records, or checking for the presence of such records through the nslookup command.

MITRE ATT&CK coverage

TacticTechniques
Credential AccessT1187 Forced Authentication, T1557.001 Adversary-in-the-Middle: Name Resolution Poisoning and SMB Relay
CollectionT1557.001 Adversary-in-the-Middle: Name Resolution Poisoning and SMB Relay

Event coverage

ProviderEventTitle
SysmonEvent ID 1Process creation
Security-AuditingEvent ID 4688A new process has been created.

Rule body yaml

title: Attempts of Kerberos Coercion Via DNS SPN Spoofing
id: 0ed99dda-6a35-11ef-8c99-0242ac120002
related:
    - id: b07e58cf-cacc-4135-8473-ccb2eba63dd2
      type: similar
status: experimental
description: |
    Detects the presence of "UWhRC....AAYBAAAA" pattern in command line.
    The pattern "1UWhRCAAAAA..BAAAA" is a base64-encoded signature that corresponds to a marshaled CREDENTIAL_TARGET_INFORMATION structure.
    Attackers can use this technique to coerce authentication from victim systems to attacker-controlled hosts.
    It is one of the strong indicators of a Kerberos coercion attack, where adversaries manipulate DNS records
    to spoof Service Principal Names (SPNs) and redirect authentication requests like in CVE-2025-33073.
    If you see this pattern in the command line, it is likely an attempt to add spoofed Service Principal Names (SPNs) to DNS records,
    or checking for the presence of such records through the `nslookup` command.
references:
    - https://www.synacktiv.com/publications/ntlm-reflection-is-dead-long-live-ntlm-reflection-an-in-depth-analysis-of-cve-2025
    - https://googleprojectzero.blogspot.com/2021/10/using-kerberos-for-authentication-relay.html
author: Swachchhanda Shrawan Poudel (Nextron Systems)
date: 2025-06-20
tags:
    - attack.collection
    - attack.credential-access
    - attack.persistence
    - attack.privilege-escalation
    - attack.t1557.001
    - attack.t1187
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        CommandLine|contains|all:
            - 'UWhRCA'
            - 'BAAAA'
    condition: selection
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: condition

selection

Stage 1: selection

selection:
    CommandLine|contains|all:
        - 'UWhRCA'
        - 'BAAAA'

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.

FieldKindValues
CommandLinematch
  • BAAAA
  • UWhRCA