Lettr — the complete, unedited output of the deterministic mcptrustchecker engine v1.13.0, scanned . Every finding, capability tag and score component below is exactly what the engine produced — no AI, no post-processing.
{
"tool": {
"name": "mcptrustchecker",
"version": "1.13.0",
"methodologyVersion": "mcptrustchecker-1.13"
},
"target": {
"id": "lettr-mcp",
"source": {
"kind": "package",
"origin": "lettr-mcp"
},
"server": {
"name": "lettr-mcp"
}
},
"grade": "A",
"score": {
"score": 94,
"threatScore": 100,
"grade": "A",
"band": "A",
"categorySubtotals": {
"injection": 0,
"exfiltration": 0,
"permissions": 0,
"supply-chain": 0,
"network": 0,
"hygiene": 0
},
"vector": [
{
"kind": "client",
"term": "capability-exposure",
"level": "high",
"label": "capability blast radius (high) — client exposure if the model is manipulated",
"appliedPenalty": 6
},
{
"kind": "client",
"term": "verification-discount",
"level": "source",
"label": "publisher verification (provenance) — cryptographic build provenance ties the artifact to its source",
"appliedPenalty": 0
},
{
"kind": "client",
"term": "coverage-honesty",
"level": "source",
"label": "inspection depth (source) — how much of the target the scan could see",
"appliedPenalty": 0
}
],
"gatesFired": [],
"methodologyVersion": "mcptrustchecker-1.13"
},
"capability": {
"level": "high",
"reasons": [
"can send data / act on an external service",
"reads sensitive or local data",
"has a read → egress path (a data-exfiltration surface)"
],
"tags": [
"external-sink",
"sensitive-source"
]
},
"coverage": {
"level": "source",
"inputs": {
"toolSurface": true,
"implementationSource": true,
"packageMetadata": true,
"liveTransport": false
},
"caveats": [
"Tools were statically extracted from the published source (68 recovered), not enumerated from a running server. Tool-poisoning, Unicode-smuggling, capability and toxic-flow analysis ran on this inferred surface, but a mis-parsed registration could be missed or mis-attributed, so tool-derived findings are capped below “confirmed”. To grade the real runtime surface, scan the running server: --command \"npx -y <package>\"."
]
},
"findings": [
{
"ruleId": "MTC-FLOW-003",
"title": "Read-and-egress in one tool: \"create-webhook\"",
"category": "exfiltration",
"severity": "high",
"confidence": "strong",
"description": "Tool \"create-webhook\" can both read sensitive data and send data to an external destination. Even without an explicit untrusted-input leg, this is a single-call data-exfiltration path if the model is ever manipulated.",
"remediation": "Separate reading from sending; require explicit user confirmation before egress of file/secret contents.",
"location": {
"kind": "flow",
"name": "create-webhook"
},
"owasp": "LLM02:2025 Sensitive Information Disclosure",
"references": [],
"data": {
"tags": [
"external-sink",
"sensitive-source"
]
}
},
{
"ruleId": "MTC-FLOW-003",
"title": "Read-and-egress in one tool: \"update-webhook\"",
"category": "exfiltration",
"severity": "high",
"confidence": "strong",
"description": "Tool \"update-webhook\" can both read sensitive data and send data to an external destination. Even without an explicit untrusted-input leg, this is a single-call data-exfiltration path if the model is ever manipulated.",
"remediation": "Separate reading from sending; require explicit user confirmation before egress of file/secret contents.",
"location": {
"kind": "flow",
"name": "update-webhook"
},
"owasp": "LLM02:2025 Sensitive Information Disclosure",
"references": [],
"data": {
"tags": [
"external-sink",
"sensitive-source"
]
}
},
{
"ruleId": "MTC-FLOW-004",
"title": "Sensitive-source and external-sink co-exist",
"category": "exfiltration",
"severity": "high",
"confidence": "strong",
"description": "Tools that read sensitive data ([create-webhook, update-webhook]) and tools that can send data out ([send-email, schedule-email, create-webhook, update-webhook, delete-webhook]) are exposed together. An agent can move private data to the sink.",
"remediation": "Keep secret-reading and egress capabilities on separate, separately-approved servers.",
"location": {
"kind": "flow",
"name": "create-webhook → send-email"
},
"evidence": "sources [create-webhook, update-webhook] → sinks [send-email, schedule-email, create-webhook, update-webhook, delete-webhook]",
"owasp": "LLM02:2025 Sensitive Information Disclosure",
"references": [],
"data": {
"sources": [
"create-webhook",
"update-webhook"
],
"sinks": [
"send-email",
"schedule-email",
"create-webhook",
"update-webhook",
"delete-webhook"
]
}
},
{
"ruleId": "MTC-CAP-007",
"title": "Unconstrained URL/host parameter \"url\" on \"create-webhook\"",
"category": "network",
"severity": "medium",
"confidence": "heuristic",
"description": "Tool \"create-webhook\" takes a URL/host parameter \"url\" with no allowlist/pattern. An outbound-request tool with an unbounded destination enables SSRF and cloud-metadata access (e.g. 169.254.169.254).",
"remediation": "Allowlist destinations or constrain the parameter; block private/link-local addresses server-side.",
"location": {
"kind": "tool",
"name": "create-webhook",
"field": "inputSchema.properties.url"
},
"owasp": "LLM06:2025 Excessive Agency",
"data": {
"param": "url"
}
},
{
"ruleId": "MTC-CAP-007",
"title": "Unconstrained URL/host parameter \"oauth_token_url\" on \"create-webhook\"",
"category": "network",
"severity": "medium",
"confidence": "heuristic",
"description": "Tool \"create-webhook\" takes a URL/host parameter \"oauth_token_url\" with no allowlist/pattern. An outbound-request tool with an unbounded destination enables SSRF and cloud-metadata access (e.g. 169.254.169.254).",
"remediation": "Allowlist destinations or constrain the parameter; block private/link-local addresses server-side.",
"location": {
"kind": "tool",
"name": "create-webhook",
"field": "inputSchema.properties.oauth_token_url"
},
"owasp": "LLM06:2025 Excessive Agency",
"data": {
"param": "oauth_token_url"
}
},
{
"ruleId": "MTC-CAP-007",
"title": "Unconstrained URL/host parameter \"url\" on \"update-webhook\"",
"category": "network",
"severity": "medium",
"confidence": "heuristic",
"description": "Tool \"update-webhook\" takes a URL/host parameter \"url\" with no allowlist/pattern. An outbound-request tool with an unbounded destination enables SSRF and cloud-metadata access (e.g. 169.254.169.254).",
"remediation": "Allowlist destinations or constrain the parameter; block private/link-local addresses server-side.",
"location": {
"kind": "tool",
"name": "update-webhook",
"field": "inputSchema.properties.url"
},
"owasp": "LLM06:2025 Excessive Agency",
"data": {
"param": "url"
}
},
{
"ruleId": "MTC-CAP-007",
"title": "Unconstrained URL/host parameter \"oauth_token_url\" on \"update-webhook\"",
"category": "network",
"severity": "medium",
"confidence": "heuristic",
"description": "Tool \"update-webhook\" takes a URL/host parameter \"oauth_token_url\" with no allowlist/pattern. An outbound-request tool with an unbounded destination enables SSRF and cloud-metadata access (e.g. 169.254.169.254).",
"remediation": "Allowlist destinations or constrain the parameter; block private/link-local addresses server-side.",
"location": {
"kind": "tool",
"name": "update-webhook",
"field": "inputSchema.properties.oauth_token_url"
},
"owasp": "LLM06:2025 Excessive Agency",
"data": {
"param": "oauth_token_url"
}
}
],
"toxicFlows": [
{
"id": "flow-1",
"severity": "high",
"confidence": "strong",
"untrustedInput": [],
"sensitiveSource": [
"create-webhook"
],
"externalSink": [
"create-webhook"
],
"selfContained": true,
"description": "Tool \"create-webhook\" both reads sensitive data and can send it externally."
},
{
"id": "flow-2",
"severity": "high",
"confidence": "strong",
"untrustedInput": [],
"sensitiveSource": [
"update-webhook"
],
"externalSink": [
"update-webhook"
],
"selfContained": true,
"description": "Tool \"update-webhook\" both reads sensitive data and can send it externally."
},
{
"id": "flow-3",
"severity": "high",
"confidence": "strong",
"untrustedInput": [],
"sensitiveSource": [
"create-webhook",
"update-webhook"
],
"externalSink": [
"send-email",
"schedule-email",
"create-webhook",
"update-webhook",
"delete-webhook"
],
"selfContained": false,
"path": [
"create-webhook",
"delete-webhook"
],
"pathWired": false,
"description": "A sensitive-source → external-sink chain exists: create-webhook → delete-webhook."
}
],
"capabilities": [
{
"tool": "list-audience-contacts",
"tags": [],
"reasons": {}
},
{
"tool": "get-audience-contact",
"tags": [],
"reasons": {}
},
{
"tool": "create-audience-contact",
"tags": [],
"reasons": {}
},
{
"tool": "bulk-create-audience-contacts",
"tags": [],
"reasons": {}
},
{
"tool": "update-audience-contact",
"tags": [],
"reasons": {}
},
{
"tool": "delete-audience-contact",
"tags": [],
"reasons": {}
},
{
"tool": "list-audience-lists",
"tags": [],
"reasons": {}
},
{
"tool": "create-audience-list",
"tags": [],
"reasons": {}
},
{
"tool": "get-audience-list",
"tags": [],
"reasons": {}
},
{
"tool": "update-audience-list",
"tags": [],
"reasons": {}
},
{
"tool": "delete-audience-list",
"tags": [],
"reasons": {}
},
{
"tool": "bulk-delete-audience-lists",
"tags": [],
"reasons": {}
},
{
"tool": "attach-contact-to-list",
"tags": [],
"reasons": {}
},
{
"tool": "detach-contact-from-list",
"tags": [],
"reasons": {}
},
{
"tool": "subscribe-contact-to-topic",
"tags": [],
"reasons": {}
},
{
"tool": "unsubscribe-contact-from-topic",
"tags": [],
"reasons": {}
},
{
"tool": "bulk-attach-contacts-to-lists",
"tags": [],
"reasons": {}
},
{
"tool": "bulk-detach-contacts-from-lists",
"tags": [],
"reasons": {}
},
{
"tool": "bulk-subscribe-contacts-to-topics",
"tags": [],
"reasons": {}
},
{
"tool": "bulk-unsubscribe-contacts-from-topics",
"tags": [],
"reasons": {}
},
{
"tool": "list-audience-properties",
"tags": [],
"reasons": {}
},
{
"tool": "create-audience-property",
"tags": [],
"reasons": {}
},
{
"tool": "get-audience-property",
"tags": [],
"reasons": {}
},
{
"tool": "update-audience-property",
"tags": [],
"reasons": {}
},
{
"tool": "delete-audience-property",
"tags": [],
"reasons": {}
},
{
"tool": "list-audience-segments",
"tags": [],
"reasons": {}
},
{
"tool": "create-audience-segment",
"tags": [],
"reasons": {}
},
{
"tool": "get-audience-segment",
"tags": [],
"reasons": {}
},
{
"tool": "update-audience-segment",
"tags": [],
"reasons": {}
},
{
"tool": "delete-audience-segment",
"tags": [],
"reasons": {}
},
{
"tool": "list-audience-topics",
"tags": [],
"reasons": {}
},
{
"tool": "create-audience-topic",
"tags": [],
"reasons": {}
},
{
"tool": "get-audience-topic",
"tags": [],
"reasons": {}
},
{
"tool": "update-audience-topic",
"tags": [],
"reasons": {}
},
{
"tool": "delete-audience-topic",
"tags": [],
"reasons": {}
},
{
"tool": "list-campaigns",
"tags": [],
"reasons": {}
},
{
"tool": "get-campaign",
"tags": [],
"reasons": {}
},
{
"tool": "list-campaign-events",
"tags": [],
"reasons": {}
},
{
"tool": "send-campaign",
"tags": [],
"reasons": {}
},
{
"tool": "schedule-campaign",
"tags": [],
"reasons": {}
},
{
"tool": "unschedule-campaign",
"tags": [],
"reasons": {}
},
{
"tool": "list-domains",
"tags": [],
"reasons": {}
},
{
"tool": "create-domain",
"tags": [],
"reasons": {}
},
{
"tool": "get-domain",
"tags": [],
"reasons": {}
},
{
"tool": "delete-domain",
"tags": [],
"reasons": {}
},
{
"tool": "verify-domain",
"tags": [],
"reasons": {}
},
{
"tool": "send-email",
"tags": [
"external-sink"
],
"reasons": {
"external-sink": [
"keyword \"send_email\""
]
}
},
{
"tool": "list-emails",
"tags": [],
"reasons": {}
},
{
"tool": "list-email-events",
"tags": [],
"reasons": {}
},
{
"tool": "get-email-detail",
"tags": [],
"reasons": {}
},
{
"tool": "schedule-email",
"tags": [
"external-sink"
],
"reasons": {
"external-sink": [
"keyword \"send_email\""
]
}
},
{
"tool": "get-scheduled-email",
"tags": [],
"reasons": {}
},
{
"tool": "cancel-scheduled-email",
"tags": [],
"reasons": {}
},
{
"tool": "list-projects",
"tags": [],
"reasons": {}
},
{
"tool": "health-check",
"tags": [],
"reasons": {}
},
{
"tool": "auth-check",
"tags": [],
"reasons": {}
},
{
"tool": "list-templates",
"tags": [],
"reasons": {}
},
{
"tool": "get-template",
"tags": [],
"reasons": {}
},
{
"tool": "create-template",
"tags": [],
"reasons": {}
},
{
"tool": "update-template",
"tags": [],
"reasons": {}
},
{
"tool": "delete-template",
"tags": [],
"reasons": {}
},
{
"tool": "get-merge-tags",
"tags": [],
"reasons": {}
},
{
"tool": "get-template-html",
"tags": [],
"reasons": {}
},
{
"tool": "list-webhooks",
"tags": [],
"reasons": {}
},
{
"tool": "get-webhook",
"tags": [],
"reasons": {}
},
{
"tool": "create-webhook",
"tags": [
"external-sink",
"sensitive-source"
],
"reasons": {
"external-sink": [
"keyword \"webhook\""
],
"sensitive-source": [
"parameter \"secret\""
]
}
},
{
"tool": "update-webhook",
"tags": [
"external-sink",
"sensitive-source"
],
"reasons": {
"external-sink": [
"keyword \"webhook\""
],
"sensitive-source": [
"parameter \"secret\""
]
}
},
{
"tool": "delete-webhook",
"tags": [
"external-sink"
],
"reasons": {
"external-sink": [
"keyword \"webhook\""
]
}
}
],
"surfaceDigest": "f3303b1fa433c798d82c18e32b71624b71b5d4c6b2988b087f9a3f4b5714d413",
"stats": {
"tools": 68,
"prompts": 0,
"resources": 0,
"findingsBySeverity": {
"critical": 0,
"high": 3,
"medium": 4,
"low": 0,
"info": 0
}
}
}