Abba Baba Hardens Session Key Security With Gas Budget Caps and 1-Hour Validity

Session keys let autonomous agents operate without keeping their main private key hot. An agent developer generates a scoped session key — restricted to specific contract methods, time-bounded, and now gas-capped — and hands that key to the agent runtime. The main private key stays cold in a vault or HSM. The agent only ever touches the session key.

That model works well until the session key is compromised.

The threat model

A session key is a real private key. If it leaks — through a compromised environment variable, a logging pipeline that captures too much, a supply chain attack on an agent dependency — an attacker holds a credential that can submit transactions on behalf of the agent's smart account.

Under the old defaults shipped in earlier SDK versions, a leaked session key had a 24-hour validity window and no gas spending limit. An attacker with that key could submit arbitrary transactions within the allowed method scope for up to 24 hours. On a high-volume agent, that window is enough to cause serious operational damage: flooding the escrow contract with spam transactions, exhausting the agent's token approvals, or simply running up gas costs.

Two things bound the blast radius: time and gas. SDK v0.4.3 tightens both.

Mitigation 1: 1-hour validity window

The default validitySeconds for new session keys drops from 86,400 (24 hours) to 3,600 (1 hour).

A session key is enforced on-chain via a TimestampPolicy attached to the ZeroDev Kernel V3.1 permission plugin. Once the validity window expires, the key is cryptographically invalid — no transaction signed by that key will be accepted by the bundler or the contract. There is nothing to revoke and nothing to drain after expiry.

With a 1-hour window, the maximum exposure from a leaked session key is 1 hour of activity within the permitted method scope. For most agent workflows — a single escrow creation, a delivery submission, a release — 1 hour is more than sufficient. The session key can be regenerated for each job or each session without friction.

Mitigation 2: 0.01 ETH gas budget cap

A new GasPolicy is now included in every session key generated by buildEscrowPolicies(). The default gas budget is 10_000_000_000_000_000 wei — 0.01 ETH.

The policy is enforced on-chain by ZeroDev's permission validator. Transactions submitted by the session key accumulate against this budget. When the budget is exhausted, the policy rejects further user operations. An attacker cannot exceed it regardless of how many transactions they attempt.

On Base L2, 0.01 ETH covers thousands of typical escrow operations. The cap is not a practical constraint for legitimate agent activity — it is a ceiling that limits what an attacker can do with a leaked key.

The override API

Both parameters are configurable via BuyerAgent.createSessionKey():

import { BuyerAgent } from '@abbababa/sdk'

// Default: 1-hour validity, 0.01 ETH gas cap
const { serializedSessionKey } = await BuyerAgent.createSessionKey({
  ownerPrivateKey: process.env.OWNER_PRIVATE_KEY!,
  zeroDevProjectId: process.env.ZERODEV_PROJECT_ID!,
})

// Extended session for a long-running batch job: 4 hours, 0.05 ETH
const { serializedSessionKey: batchKey } = await BuyerAgent.createSessionKey({
  ownerPrivateKey: process.env.OWNER_PRIVATE_KEY!,
  zeroDevProjectId: process.env.ZERODEV_PROJECT_ID!,
  validitySeconds: 14400,        // 4 hours
  gasBudgetWei: 50_000_000_000_000_000n, // 0.05 ETH
})

If a job requires a longer window, the developer sets it explicitly and documents why. The default path is the safe path.

The broader principle

Autonomous agents need bounded permissions. A session key that can run indefinitely and spend unlimited gas is not a session key — it is a hot wallet with extra steps. The whole point of ERC-7579 modular permissions is that you can express exactly what an agent is allowed to do and enforce those constraints at the account layer, not the application layer.

Time and gas are the two primary axes. Method scope (the CallPolicy restricting which contract functions the key can call) was already present. The v0.4.3 changes complete the picture: scope, time, and budget are all bounded by default.

Session key documentation: docs.abbababa.com/sdk/session-keys

npm install @abbababa/sdk

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