$50M Token Swap Loss: Aave Blames the User While CoW Swap Points to Technical Failures

Two Investigations, Two Contradicting Narratives

On March 14, both Aave and CoW Swap published their own post-mortem analyses of an incident in which a single user lost more than $50 million during a token swap. The two protocols reached starkly different conclusions: CoW Swap attributes the loss to a cascade of technical failures, while Aave places responsibility on the user's decision-making and the illiquidity of the trading pair.

Why This Matters

A $50 million loss from a single swap operation ranks among the largest such incidents in DeFi history. The event exposed multiple systemic vulnerabilities — from outdated code in aggregator infrastructure to the ineffectiveness of anti-MEV protections. The fact that two major protocols arrived at fundamentally different explanations raises critical questions about who bears responsibility for user safety in decentralized finance.

CoW Swap's Account: A Perfect Storm of Technical Failures

The CoW Swap team described the incident as the convergence of several simultaneous failures: a fill-or-kill order on an illiquid pair with massive volume, an outdated gas limit in the verification system, a solver that failed to execute, and a potential data leak from the private mempool.

"https://t.co/1JJhoyi3Pd" — CoW DAO (@CoWSwap), original post

During the quote-gathering phase, three solvers submitted prices. The best of these offered roughly $5 million worth of AAVE for $50 million — representing approximately a 90% loss. However, the verification system, hardcoded with a 12 million gas limit (legacy code, as CoW acknowledged), rejected these quotes. The only quote that passed verification came from Solver A, offering approximately 329 AAVE — 150 to 200 times worse than the rejected alternatives. This became the basis for the order's limit price.

Execution made things worse. Solver E found a more favorable route and won two consecutive auctions, but neither transaction was included in a block. After two failed attempts, Solver E stopped competing, leaving only the weakest solver with the worst price. CoW acknowledged that the auction mechanism has no safeguard to detect such scenarios.

The team also flagged signs of a mempool leak. The transaction was submitted through a private RPC, yet it received a "confirmed within 30 seconds" label — a pattern consistent with the transaction appearing in the public queue before block inclusion. The investigation remains ongoing.

Aave's Account: User Error and Illiquidity

Aave reconstructed the trade route: the solver converted aEthUSDT to USDT via Aave V3, swapped it to WETH on Uniswap V3, and finalized the transaction through a SushiSwap pool holding just $73,000 in liquidity.

"https://t.co/UmXulxU7NS" — Aave (@aave), original post

Aave emphasized that the swap widget displayed a warning about "high price impact (99.9%)" and required the user to check an acknowledgment box. The trader confirmed the operation from a mobile device. The funds remain accessible at the user's address, but the individual has not made contact.

In response to the incident, Aave launched Aave Shield, a new feature that blocks all swap operations with price impact exceeding 25% by default. Users can only disable this protection manually through settings.

Project founder Stani Kulechov had previously mentioned plans to return approximately $600,000 in fees. The latest publication revised this figure to $110,368 (25 basis points), a number confirmed by CoW Swap aggregator metadata. The distribution of these funds has become a governance dispute: since December 2025, Aave DAO participants have been unable to agree on whether to send the money to the DAO treasury or to Aave Labs developers.

The MEV Elephant in the Room

Neither official report meaningfully addresses the MEV bots that captured the lion's share of value from the trader's mistake. According to Arkham data, the Titan Builder algorithm extracted approximately $34 million in ETH. A separate bot netted $9.9 million through a successful sandwich attack.

"Titan Builder extracted $34M worth of ETH out of this debacle. They immediately sent all proceeds to Coinbase" — Emmett Gallic (@emmettgallic), original post

CoW Swap only referenced "significant backrun" and listed wallet addresses, but avoided using the term "sandwich attack" and did not explain the mechanics. This omission is particularly notable given that CoW Swap's integration with Aave was specifically marketed as MEV protection.

For context, just days earlier on March 10, Aave had already dealt with a separate incident — an oracle malfunction that triggered erroneous liquidations of wstETH positions totaling approximately $26 million.