decrypt_attachment
AI agents call decrypt_attachment to retrieve information from Mcp Signal without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
The tool appears to decrypt and retrieve attachment data from Signal messages. While the description is empty (reducing confidence slightly), the name and server purpose—'read via Signal Desktop'—indicate this is a data retrieval operation with no side effects. Decryption is a read operation that extracts existing data without modifying or deleting it.
From the tool's definition Tool name 'decrypt_attachment' and server context (Signal MCP for reading Signal Desktop data) indicate retrieval of encrypted message attachments.
Attacks that exploit this kind of access
decrypt_attachment. It is categorised as a Read tool in the Mcp Signal MCP Server, which means it retrieves data without modifying state.
Register the Mcp Signal MCP server in PolicyLayer and add a rule for decrypt_attachment: 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 Mcp Signal. Nothing to install.
decrypt_attachment is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the decrypt_attachment 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 decrypt_attachment. 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.
decrypt_attachment is provided by the Mcp Signal MCP server (sealjay/mcp-signal). 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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