Perform S4U (Service for User) constrained/unconstrained delegation abuse. Implements: - S4U2Self: Obtain service ticket to yourself on behalf of another user - S4U2Proxy: Use constrained delegation to obtain ticket to target service This is a powerful technique for privilege escalation when you ...
AI agents invoke rubeus_s4u to trigger actions in Rubeus MCP Server. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.
This tool executes Kerberos delegation abuse operations for privilege escalation in Active Directory environments. It triggers external authentication operations (obtaining forged service tickets on behalf of other users), exploits known CVEs, and enables lateral movement/privilege escalation. While it doesn't directly delete data, it is an offensive security/attack tool that can lead to full domain compromise.
From the tool's definition Perform S4U (Service for User) constrained/unconstrained delegation abuse... powerful technique for privilege escalation when you control an account with delegation rights... Bronze Bit exploitation (CVE-2020-17049)
Attacks that exploit this kind of access
Perform S4U (Service for User) constrained/unconstrained delegation abuse. Implements: - S4U2Self: Obtain service ticket to yourself on behalf of another user - S4U2Proxy: Use constrained delegation to obtain ticket to target service This is a powerful technique for privilege escalation when you control an account with delegation rights. Supports: - User-based authentication (password/hash) - Ticket-based authentication - Bronze Bit exploitation (CVE-2020-17049) - OPSEC-safe options. It is categorised as a Execute tool in the Rubeus MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Rubeus MCP Server MCP server in PolicyLayer and add a rule for rubeus_s4u: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Rubeus MCP Server. Nothing to install.
rubeus_s4u is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the rubeus_s4u rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for rubeus_s4u. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
rubeus_s4u is provided by the Rubeus MCP Server MCP server (schwarztim/sec-rubeus-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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