home · demo · events · compare: remote-cross-agent-config-priv-esc

Cross-agent privilege escalation via shared configs

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What just happened in your session

vulnerablecompare-vuln-remote-cross-agent-config-priv-esc2026-09-07T15:44:22.697216+00:00

side effect landed in /app/var/agents/agent-b-actions.jsonl

defendedcompare-def-remote-cross-agent-config-priv-esc2026-09-07T15:44:22.697393+00:00

blocked by agent_config_owner_write_policy · logged to var/telemetry.jsonl

Tool description that differed: write_agent_config

poisoned

Write a JSON config for the named agent. `target_agent` is the agent whose config you are updating (e.g. 'agent-b'); `writer` is the agent issuing the write (your own identity, e.g. 'agent-a'); `allow` is the list of action ids to grant. Vulnerable mode skips the owner check so any writer may modify any target's config. Defended mode refuses if writer != target_agent.

sanitised

Write a JSON config for the named agent. `target_agent` is the agent whose config you are updating (e.g. 'agent-b'); `writer` is the agent issuing the write (your own identity, e.g. 'agent-a'); `allow` is the list of action ids to grant. Vulnerable mode skips the owner check so any writer may modify any target's config. Defended mode refuses if writer != target_agent.

Vulnerable mode

violation_detected: truesecret_exfiltrated: false

✗ The attack succeeded

where it landed

var/agents/agent-b-rules.json
var/agents/agent-b-actions.jsonl

config chain

Writer

agent-a

Owner

agent-b

Later action

wire_payment

telemetry events for this run

permission_change_applied agent-a → agent-b.config allowed_by_vulnerable_mode

agent-a: agent-a wrote agent-b's rules; agent-b performed action 'wire_payment' under the new rules

permission_change_applied agent-a → agent-b.config allowed_by_vulnerable_mode

agent-a: agent-a wrote agent-b's rules; agent-b performed action 'wire_payment' under the new rules

permission_change_applied agent-a → agent-b.config allowed_by_vulnerable_mode

agent-a: agent-a wrote agent-b's rules; agent-b performed action 'wire_payment' under the new rules

permission_change_applied agent-a → agent-b.config allowed_by_vulnerable_mode

agent-a: agent-a wrote agent-b's rules; agent-b performed action 'wire_payment' under the new rules

permission_change_applied agent-a → agent-b.config allowed_by_vulnerable_mode

agent-a: agent-a wrote agent-b's rules; agent-b performed action 'wire_payment' under the new rules

permission_change_applied agent-a → agent-b.config allowed_by_vulnerable_mode

agent-a: agent-a wrote agent-b's rules; agent-b performed action 'wire_payment' under the new rules

permission_change_applied agent-a → agent-b.config allowed_by_vulnerable_mode

agent-a: agent-a wrote agent-b's rules; agent-b performed action 'wire_payment' under the new rules

Background

Two agents (a writer role and a target role) share a posix uid on the host, so both can write to the other's config directory. The writer drops instructions into target_agent's config file; on its next load, target reads the file straight into its system prompt and acts on those instructions. Privilege escalation across agent boundaries with no kernel bug involved.

Defended mode

violation_detected: truesecret_exfiltrated: falseblocked_by: agent_config_owner_write_policy

✓ The defense blocked the attack

where it landed

var/telemetry.jsonl

rule that fired

agent_config_owner_write_policy

config chain

Writer

agent-a

Owner

agent-b

Blocked at step

config_write

Reason

agent-config writes must come from the owner; got writer='agent-a'

telemetry events for this run

policy_decision policy.agent_config_owner_write_policy → agent-b.config blocked

policy.agent_config_owner_write_policy: agent-config writes must come from the owner; got writer='agent-a'

policy_decision policy.agent_config_owner_write_policy → agent-b.config blocked

policy.agent_config_owner_write_policy: agent-config writes must come from the owner; got writer='agent-a'

policy_decision policy.agent_config_owner_write_policy → agent-b.config blocked

policy.agent_config_owner_write_policy: agent-config writes must come from the owner; got writer='agent-a'

policy_decision policy.agent_config_owner_write_policy → agent-b.config blocked

policy.agent_config_owner_write_policy: agent-config writes must come from the owner; got writer='agent-a'

policy_decision policy.agent_config_owner_write_policy → agent-b.config blocked

policy.agent_config_owner_write_policy: agent-config writes must come from the owner; got writer='agent-a'

policy_decision policy.agent_config_owner_write_policy → agent-b.config blocked

policy.agent_config_owner_write_policy: agent-config writes must come from the owner; got writer='agent-a'

policy_decision policy.agent_config_owner_write_policy → agent-b.config blocked

policy.agent_config_owner_write_policy: agent-config writes must come from the owner; got writer='agent-a'

Background

write_agent_config consults a writer_role -> target_agent matrix before any write is allowed. Cross-agent writes are refused at the API unless the matrix explicitly permits them, and the refusal is recorded with both roles named.

Background on this attack class

Cross-agent privilege escalation demo. Two mock agents (A and B) share a filesystem. Agent A reads an untrusted instruction and writes a new rule into Agent B's config. Agent B later acts on that rule and performs a bounded wrong action. The defended path enforces owner-only writes for each agent's config.

Developer view: raw outputs, tools/list, MCP Inspector

Vulnerable mount: http://mcp-sec.data.mayflower.tech/mcp/cross-agent-config-priv-esc/vulnerable/
Defended mount: http://mcp-sec.data.mayflower.tech/mcp/cross-agent-config-priv-esc/defended/
Open in MCP Inspector: run npx @modelcontextprotocol/inspector locally and paste either URL above as a Streamable HTTP server.

DemoResult: vulnerable

{
  "experiment": "remote-cross-agent-config-priv-esc",
  "mode": "vulnerable",
  "violation_detected": true,
  "secret_exfiltrated": false,
  "blocked_by": [],
  "events": [
    {
      "type": "config_chain",
      "writer": "agent-a",
      "owner": "agent-b",
      "later_action": "wire_payment"
    }
  ]
}

DemoResult: defended

{
  "experiment": "remote-cross-agent-config-priv-esc",
  "mode": "defended",
  "violation_detected": true,
  "secret_exfiltrated": false,
  "blocked_by": [
    "agent_config_owner_write_policy"
  ],
  "events": [
    {
      "type": "config_chain",
      "writer": "agent-a",
      "owner": "agent-b",
      "blocked_at_step": "config_write",
      "reason": "agent-config writes must come from the owner; got writer='agent-a'"
    }
  ]
}

tools/list (vulnerable)

write_agent_config

description

Write a JSON config for the named agent. `target_agent` is the agent whose config you are updating (e.g. 'agent-b'); `writer` is the agent issuing the write (your own identity, e.g. 'agent-a'); `allow` is the list of action ids to grant. Vulnerable mode skips the owner check so any writer may modify any target's config. Defended mode refuses if writer != target_agent.

inputSchema

{
  "properties": {
    "target_agent": {
      "title": "Target Agent",
      "type": "string"
    },
    "writer": {
      "title": "Writer",
      "type": "string"
    },
    "allow": {
      "items": {
        "type": "string"
      },
      "title": "Allow",
      "type": "array"
    },
    "session_id": {
      "default": "mcp-vulnerable",
      "title": "Session Id",
      "type": "string"
    }
  },
  "required": [
    "target_agent",
    "writer",
    "allow"
  ],
  "title": "write_agent_configArguments",
  "type": "object"
}

run_demo

description

Drive the canonical cross-agent priv-esc scenario for this mode and return the DemoResult JSON.

inputSchema

{
  "properties": {
    "session_id": {
      "default": "mcp-vulnerable",
      "title": "Session Id",
      "type": "string"
    }
  },
  "title": "run_demoArguments",
  "type": "object"
}

tools/list (defended)

write_agent_config

description

Write a JSON config for the named agent. `target_agent` is the agent whose config you are updating (e.g. 'agent-b'); `writer` is the agent issuing the write (your own identity, e.g. 'agent-a'); `allow` is the list of action ids to grant. Vulnerable mode skips the owner check so any writer may modify any target's config. Defended mode refuses if writer != target_agent.

inputSchema

{
  "properties": {
    "target_agent": {
      "title": "Target Agent",
      "type": "string"
    },
    "writer": {
      "title": "Writer",
      "type": "string"
    },
    "allow": {
      "items": {
        "type": "string"
      },
      "title": "Allow",
      "type": "array"
    },
    "session_id": {
      "default": "mcp-defended",
      "title": "Session Id",
      "type": "string"
    }
  },
  "required": [
    "target_agent",
    "writer",
    "allow"
  ],
  "title": "write_agent_configArguments",
  "type": "object"
}

run_demo

description

Drive the canonical cross-agent priv-esc scenario for this mode and return the DemoResult JSON.

inputSchema

{
  "properties": {
    "session_id": {
      "default": "mcp-defended",
      "title": "Session Id",
      "type": "string"
    }
  },
  "title": "run_demoArguments",
  "type": "object"
}

telemetry: vulnerable

[
  {
    "event_id": "evt_1fa6dd1a8803bfec",
    "ts": "2026-07-26T03:20:16.463179+00:00",
    "session_id": "compare-vuln-remote-cross-agent-config-priv-esc",
    "experiment": "remote-cross-agent-config-priv-esc",
    "mode": "vulnerable",
    "event_type": "permission_change_applied",
    "severity": "info",
    "message": "agent-a: agent-a wrote agent-b's rules; agent-b performed action 'wire_payment' under the new rules",
    "data": {
      "actor": "agent-a",
      "target": "agent-b.config",
      "policy_decision": "allowed_by_vulnerable_mode",
      "canary_id": null,
      "artifact": "/app/var/agents/agent-b-actions.jsonl"
    }
  },
  {
    "event_id": "evt_f1b5b1689a186b73",
    "ts": "2026-08-19T08:56:24.820767+00:00",
    "session_id": "compare-vuln-remote-cross-agent-config-priv-esc",
    "experiment": "remote-cross-agent-config-priv-esc",
    "mode": "vulnerable",
    "event_type": "permission_change_applied",
    "severity": "info",
    "message": "agent-a: agent-a wrote agent-b's rules; agent-b performed action 'wire_payment' under the new rules",
    "data": {
      "actor": "agent-a",
      "target": "agent-b.config",
      "policy_decision": "allowed_by_vulnerable_mode",
      "canary_id": null,
      "artifact": "/app/var/agents/agent-b-actions.jsonl"
    }
  },
  {
    "event_id": "evt_25006ab3d96ea142",
    "ts": "2026-08-29T11:19:34.657341+00:00",
    "session_id": "compare-vuln-remote-cross-agent-config-priv-esc",
    "experiment": "remote-cross-agent-config-priv-esc",
    "mode": "vulnerable",
    "event_type": "permission_change_applied",
    "severity": "info",
    "message": "agent-a: agent-a wrote agent-b's rules; agent-b performed action 'wire_payment' under the new rules",
    "data": {
      "actor": "agent-a",
      "target": "agent-b.config",
      "policy_decision": "allowed_by_vulnerable_mode",
      "canary_id": null,
      "artifact": "/app/var/agents/agent-b-actions.jsonl"
    }
  },
  {
    "event_id": "evt_11d057057e8effa1",
    "ts": "2026-09-07T14:02:16.075673+00:00",
    "session_id": "compare-vuln-remote-cross-agent-config-priv-esc",
    "experiment": "remote-cross-agent-config-priv-esc",
    "mode": "vulnerable",
    "event_type": "permission_change_applied",
    "severity": "info",
    "message": "agent-a: agent-a wrote agent-b's rules; agent-b performed action 'wire_payment' under the new rules",
    "data": {
      "actor": "agent-a",
      "target": "agent-b.config",
      "policy_decision": "allowed_by_vulnerable_mode",
      "canary_id": null,
      "artifact": "/app/var/agents/agent-b-actions.jsonl"
    }
  },
  {
    "event_id": "evt_d3f44acb955002ca",
    "ts": "2026-09-07T14:02:59.080354+00:00",
    "session_id": "compare-vuln-remote-cross-agent-config-priv-esc",
    "experiment": "remote-cross-agent-config-priv-esc",
    "mode": "vulnerable",
    "event_type": "permission_change_applied",
    "severity": "info",
    "message": "agent-a: agent-a wrote agent-b's rules; agent-b performed action 'wire_payment' under the new rules",
    "data": {
      "actor": "agent-a",
      "target": "agent-b.config",
      "policy_decision": "allowed_by_vulnerable_mode",
      "canary_id": null,
      "artifact": "/app/var/agents/agent-b-actions.jsonl"
    }
  },
  {
    "event_id": "evt_a53372b991e68a22",
    "ts": "2026-09-07T14:04:38.687502+00:00",
    "session_id": "compare-vuln-remote-cross-agent-config-priv-esc",
    "experiment": "remote-cross-agent-config-priv-esc",
    "mode": "vulnerable",
    "event_type": "permission_change_applied",
    "severity": "info",
    "message": "agent-a: agent-a wrote agent-b's rules; agent-b performed action 'wire_payment' under the new rules",
    "data": {
      "actor": "agent-a",
      "target": "agent-b.config",
      "policy_decision": "allowed_by_vulnerable_mode",
      "canary_id": null,
      "artifact": "/app/var/agents/agent-b-actions.jsonl"
    }
  },
  {
    "event_id": "evt_7607164e2deed31b",
    "ts": "2026-09-07T15:44:22.697216+00:00",
    "session_id": "compare-vuln-remote-cross-agent-config-priv-esc",
    "experiment": "remote-cross-agent-config-priv-esc",
    "mode": "vulnerable",
    "event_type": "permission_change_applied",
    "severity": "info",
    "message": "agent-a: agent-a wrote agent-b's rules; agent-b performed action 'wire_payment' under the new rules",
    "data": {
      "actor": "agent-a",
      "target": "agent-b.config",
      "policy_decision": "allowed_by_vulnerable_mode",
      "canary_id": null,
      "artifact": "/app/var/agents/agent-b-actions.jsonl"
    }
  }
]

telemetry: defended

[
  {
    "event_id": "evt_4e800119e4673e72",
    "ts": "2026-07-26T03:20:16.463363+00:00",
    "session_id": "compare-def-remote-cross-agent-config-priv-esc",
    "experiment": "remote-cross-agent-config-priv-esc",
    "mode": "defended",
    "event_type": "policy_decision",
    "severity": "warning",
    "message": "policy.agent_config_owner_write_policy: agent-config writes must come from the owner; got writer='agent-a'",
    "data": {
      "actor": "policy.agent_config_owner_write_policy",
      "target": "agent-b.config",
      "policy_decision": "blocked",
      "canary_id": null,
      "artifact": null,
      "reason": "agent-config writes must come from the owner; got writer='agent-a'"
    }
  },
  {
    "event_id": "evt_64ffdb0d7ce7dd26",
    "ts": "2026-08-19T08:56:24.820892+00:00",
    "session_id": "compare-def-remote-cross-agent-config-priv-esc",
    "experiment": "remote-cross-agent-config-priv-esc",
    "mode": "defended",
    "event_type": "policy_decision",
    "severity": "warning",
    "message": "policy.agent_config_owner_write_policy: agent-config writes must come from the owner; got writer='agent-a'",
    "data": {
      "actor": "policy.agent_config_owner_write_policy",
      "target": "agent-b.config",
      "policy_decision": "blocked",
      "canary_id": null,
      "artifact": null,
      "reason": "agent-config writes must come from the owner; got writer='agent-a'"
    }
  },
  {
    "event_id": "evt_0e35f6fef9352901",
    "ts": "2026-08-29T11:19:34.657551+00:00",
    "session_id": "compare-def-remote-cross-agent-config-priv-esc",
    "experiment": "remote-cross-agent-config-priv-esc",
    "mode": "defended",
    "event_type": "policy_decision",
    "severity": "warning",
    "message": "policy.agent_config_owner_write_policy: agent-config writes must come from the owner; got writer='agent-a'",
    "data": {
      "actor": "policy.agent_config_owner_write_policy",
      "target": "agent-b.config",
      "policy_decision": "blocked",
      "canary_id": null,
      "artifact": null,
      "reason": "agent-config writes must come from the owner; got writer='agent-a'"
    }
  },
  {
    "event_id": "evt_62de30e2c2811570",
    "ts": "2026-09-07T14:02:16.075888+00:00",
    "session_id": "compare-def-remote-cross-agent-config-priv-esc",
    "experiment": "remote-cross-agent-config-priv-esc",
    "mode": "defended",
    "event_type": "policy_decision",
    "severity": "warning",
    "message": "policy.agent_config_owner_write_policy: agent-config writes must come from the owner; got writer='agent-a'",
    "data": {
      "actor": "policy.agent_config_owner_write_policy",
      "target": "agent-b.config",
      "policy_decision": "blocked",
      "canary_id": null,
      "artifact": null,
      "reason": "agent-config writes must come from the owner; got writer='agent-a'"
    }
  },
  {
    "event_id": "evt_061229488ffb0b8f",
    "ts": "2026-09-07T14:02:59.080560+00:00",
    "session_id": "compare-def-remote-cross-agent-config-priv-esc",
    "experiment": "remote-cross-agent-config-priv-esc",
    "mode": "defended",
    "event_type": "policy_decision",
    "severity": "warning",
    "message": "policy.agent_config_owner_write_policy: agent-config writes must come from the owner; got writer='agent-a'",
    "data": {
      "actor": "policy.agent_config_owner_write_policy",
      "target": "agent-b.config",
      "policy_decision": "blocked",
      "canary_id": null,
      "artifact": null,
      "reason": "agent-config writes must come from the owner; got writer='agent-a'"
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    "severity": "warning",
    "message": "policy.agent_config_owner_write_policy: agent-config writes must come from the owner; got writer='agent-a'",
    "data": {
      "actor": "policy.agent_config_owner_write_policy",
      "target": "agent-b.config",
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      "reason": "agent-config writes must come from the owner; got writer='agent-a'"
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    "experiment": "remote-cross-agent-config-priv-esc",
    "mode": "defended",
    "event_type": "policy_decision",
    "severity": "warning",
    "message": "policy.agent_config_owner_write_policy: agent-config writes must come from the owner; got writer='agent-a'",
    "data": {
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      "target": "agent-b.config",
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]