Suspicious Kerberos RC4 Ticket Encryption

Severity: medium
Author: Florian Roth (Nextron Systems)
Source: upstream

Detects service ticket requests using RC4 encryption type

MITRE ATT&CK coverage

Tactic	Techniques
Credential Access	`T1558.003` Steal or Forge Kerberos Tickets: Kerberoasting

Event coverage

Provider	Event ID	Title
Security-Auditing	4769	A Kerberos service ticket was requested.

Stages and Predicates

Stage 1: `selection`

TicketEncryptionType: 0x17
TicketOptions: 0x40810000

Stage 2: `not reduction`

ServiceName|endswith: '$'

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
`ServiceName`	ends_with	`$` corpus 2 (sigma 2)
`TicketEncryptionType`	eq	`0x17` corpus 7 (splunk 4, sigma 3)
`TicketOptions`	eq	`0x40810000` corpus 3 (splunk 2, sigma 1)