Swaprum Backdoor Rug Pull

On May 19, 2023, the Arbitrum DEX Swaprum — a fork of Arbiswap — executed a $3 million rug pull by exploiting a hidden backdoor in an upgradeable proxy contract. The contracts had been audited; the backdoor was introduced through the proxy's upgrade mechanism after the audit. The team drained LP staking deposits and laundered the proceeds through Tornado Cash before deleting their social presence.

What happened

Swaprum presented as a legitimate DEX with staking rewards for liquidity providers. It had an audit and the usual trust signals. The technical structure of the rug:

1. Swaprum's staking contracts were behind an upgradeable proxy.
2. The audited version of the contracts was clean — which is what users and the audit reviewed.
3. After the audit, the team used the proxy's upgrade mechanism to deploy a new implementation containing a hidden backdoor: an add() function that, despite its innocuous name, allowed the contract owner to drain staked LP tokens from the protocol.
4. On May 19, the team called the backdoor function, draining approximately $3M in staked LP positions.
5. Removed liquidity, swapped to ETH, bridged off Arbitrum, and deposited into Tornado Cash.
6. Deleted the website, Twitter, Telegram, and GitHub — the standard exit-scam finishing move.

Aftermath

• No recovery — the rug was structured so the team controlled every exit path.
• The "audited" status drew renewed attention to the gap between "the audited contract is safe" and "the deployed-and-then-upgraded contract is safe."
• Swaprum joined the long 2022-2023 list of audited Arbitrum-ecosystem rug pulls.

Why it matters

Swaprum is one of the cleanest demonstrations of the upgradeable-proxy rug pattern — distinct from the simpler "team had privileged mint authority" rug (Arbix Finance) because the malicious code did not exist at audit time. The audit was, in a narrow sense, accurate: the contracts it reviewed were clean. The backdoor was introduced afterward, through the legitimate proxy-upgrade mechanism, which the audit had no way to anticipate.

The structural lessons:

1. An audit is a point-in-time assessment of specific code. If the contract is upgradeable, the audit certifies only the version reviewed — not whatever the proxy points to after the next upgrade. Users checking "is this audited?" need to also check "is this upgradeable, and who controls the upgrade key?"

2. Upgradeability is itself a risk factor that users systematically under-weight. A non-upgradeable contract that passes audit is meaningfully safer than an upgradeable one with the same audit, because the latter can become arbitrary code at the upgrade-controller's discretion.

3. Backdoor functions are often disguised with innocuous names. Swaprum's was called add(). The defensive practice — for users who can read Solidity, and for the tools that serve those who can't — is to enumerate every function callable by the contract owner/upgrader and reason about worst-case use, not to trust function names.

The post-Swaprum (and post-Hope Finance, post-Arbix) industry response has pushed toward:

• Audit reports that explicitly state the deployed bytecode hash and whether the contract is upgradeable.
• On-chain verification tools (e.g. via block explorers) that flag upgradeable proxies and identify the upgrade controller.
• Time-locked, multi-sig-gated, or renounced upgrade authority as a baseline expectation for any protocol soliciting deposits.

Swaprum remains a representative entry in the 2022-2023 wave of audited rug pulls that collectively forced the market to internalise: "audited" answers a narrow question, and the question users actually care about — "will this team take my money?" — is mostly outside an audit's scope.