Insecure Inter-Agent Communication

An inter-agent message travels through channels and intermediate agents the receiver did not originate. If nothing binds the message cryptographically to its source, any intermediate hop can substitute or inject content that the receiving agent will treat as authoritative. Message signing closes that gap: the source agent signs each message payload with its private key, and the receiver verifies the signature against a distributed trust bundle before the content reaches the reasoning layer.

In most deployments, agents authenticate to one another with long-lived bearer tokens or shared secrets. If any one of those credentials is stolen, the attacker has persistent, platform-wide access until someone manually rotates it. SPIFFE replaces that model: each workload is issued a short-lived, cryptographically verifiable identity document, and every connection requires both sides to present one. No long-lived secrets traverse the network, and a compromised credential is worthless within its TTL.

An agent that has been compromised, poisoned, or gone rogue will, in most cases, behave differently from its established baseline. Anomaly isolation acts on that difference: when an agent's behaviour score crosses a configured threshold, it is quarantined automatically, credentials revoked, message-queue access cut, in-flight actions aborted. Manual revocation cannot match the speed that cascading multi-agent failures demand.

An agent that holds a persistent catalog of invokable tools can reach any of them at any point in its session. If its reasoning is manipulated or its identity is compromised, that persistent surface is fully available to an attacker. Just-in-time tool grants remove the standing surface: a policy broker issues a time-bound, task-scoped grant immediately before the tool is needed and revokes it automatically when the task completes or the window expires.

Each tool in an agent's catalog should expose only the methods, resources, and parameter ranges its designated role requires. Over-broad tool surfaces let individually authorised primitives compose into actions no human intended to grant; narrowing the scope at design time reduces both the attack surface and the blast radius of any compromise.

An MCP server response is content the LLM will reason over next. The model cannot distinguish tool output from instruction: that boundary must be enforced at the client, before the payload enters the context window. MCP response sanitisation applies schema validation, Unicode normalisation, control-token stripping, and structural wrapping to every tool result at the response boundary, so adversarial content embedded in a server response cannot redirect the agent's planner.

A single agent's judgment on a high-impact action can be wrong, manipulated, or compromised. Requiring N of M independent peer agents to agree before the action executes means an attacker or a systematic error must affect the quorum majority, not just one agent, before harm results.

In a multi-agent system, each agent routes decisions based on what its peers report. If a peer's behaviour becomes unreliable or adversarial, agents that keep treating it with full authority will propagate whatever errors or manipulations that peer introduces. Per-agent trust scoring addresses this by maintaining a continuously updated reputation score for every peer, derived from observed behaviour, and using that score to determine how much authority each incoming message carries.

An agent identity backed by a long-lived bearer token grants access for as long as that token remains valid. If the token is stolen, logged, or extracted from a running process, the attacker holds working credentials for weeks or months without any further action. Short-lived tokens address this by issuing credentials with a time-to-live measured in minutes or hours, automated and renewed by the platform rather than a human. When a token expires, access ends: the attacker must win the renewal process as well, which requires compromising a harder target than the token itself.

A tool's description field is concatenated directly into the agent's system prompt and shapes which tools the agent selects and how it uses them. An attacker who controls or compromises a tool manifest can plant a description that overstates the tool's scope, suppresses safety scaffolding, or embeds instruction-following language aimed at the agent. Validating descriptions at catalog-load, before the tool enters the runtime, stops that class of manipulation at the registration boundary rather than detecting its effects later at the call seam.