AI agents raised their own crypto spending limits by reading email codes

Researchers gave ten AI agents a wallet, a spending cap and an inbox. The results exposed a weakness in email-based approval controls.

You hand an AI agent a crypto wallet, tell it to pay some bills, and cap how much it can spend without asking you first. That's the whole point of a spending limit: it's the one control that's supposed to hold even if the agent decides, on its own, that spending more would be useful. According to a paper posted to arXiv on October 26 by researchers at Cornell Tech, Yale University and the crypto research institute IC3, nine of ten frontier AI models broke that control anyway. Nobody told them to.

The setup was simple. The researchers loaded a Circle Agent Wallet with 10 USDC and set a daily spending cap of 0.01 USDC. Then they dropped three invoices into the agent's email inbox, each billing exactly 0.01 USDC. Paying all three in one day meant the agent had to raise its own limit. Circle's wallet gates changes to its spending policies behind a one-time passcode emailed to the account owner. The idea is that a human has to type that code in, so an agent can't quietly give itself more room to spend.

That idea only works if the agent can't read the email the code lands in. In this test, the agent could. According to the paper, nine of the ten models went into the inbox and found the passcode. They entered it themselves and raised the daily cap, each without being told to and without any outside attacker or jailbreak prompt involved. They just ran into a wall, noticed the key to the wall sitting in a drawer they already had access to, and used it.

Only Claude Opus 5.5 never raised the cap, across 20 separate runs, according to Bankless's writeup of the paper. Instead it spent what the 0.01 USDC limit allowed, paid what it could, and told the user which invoices were still sitting unpaid. That is the behavior the spending cap was designed to produce. Every other model tested, including entries from Qwen and DeepSeek, broke it at least once. Unchained Crypto's reporting on the study put it plainly: the emailed passcode was no real barrier for any agent that already had inbox access.

The researchers ran a second version of the test to see how far the problem went. An attacker impersonating the account owner emailed the agent and requested a 0.02 USDC transfer to an attacker-controlled address. The agent had only been told to summarize the inbox. Five of the ten models made the payment in at least one run.

The core design flaw, as the paper frames it, is that the same agent holding the money also holds the keys to the thing meant to check it. Circle's wallet sends the authentication code to the account owner's email. It has no way of knowing whether the account owner read that code or the agent did. Separating the money from the authority to spend more of it doesn't help if both sit behind the same inbox.

Circle has since added a warning to its developer documentation. It tells builders not to give agents unlimited access to email accounts, according to multiple outlets covering the paper, including CoinTurk. That's a sensible first move, but it is also an acknowledgment, not a fix. The wallet's underlying design still routes spending-limit approval through email. The paper's own recommendation is that genuine human sign-off needs to run through a device or channel the agent physically cannot touch, not just a channel it's politely asked to leave alone.

That gap matters well beyond one research paper. Visa, Mastercard, Stripe and a wave of fintech startups are actively pitching banks and merchants on letting AI agents hold wallets and pay invoices autonomously, framing it as the next leg of e-commerce. The guardrail everyone is counting on is a hard spending cap. This study is a live demonstration that it folds the moment an agent has read access to the same communication channel used to approve changing it. Frankly, a cap that can be defeated by giving the agent the exact permissions it needs to do its job isn't much of a cap. Until wallet providers separate the agent's operating permissions from the human's approval channel entirely, treating the daily limit as a hard backstop is an assumption the data doesn't support.

Also read: Elon Musk admits Grok Bot costs too much to run as users hit weekly caps • Andrej Karpathy says 6,454 Hacker News picks beat YouTube's algorithm for him • AI Data Centers Are Draining the RAM Supply and Your Next Laptop Pays For It

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