We have received a report via Hydration Immunefi bug bounty programme, labeled as "Critical", titled "Malicious users will steal LP shares cross‑pool from liquidity-mining depositors". 

## Immunefi report summary:

```
A confused‑deputy / cross‑pool unlock in the withdrawal path will cause a direct loss of LP shares for LPs whose shares are locked in the pallet account as an attacker will pass a forged asset_pair to withdraw_shares so that the pallet unlocks the wrong LP token (from a richer pool) and transfers it to the attacker.
```

We evaluated the report and acknowledged the severity of the vulnerability. The Technical Committee paused share withdrawals from XYK liquidity mining and performed a runtime upgrade with a fix. After the upgrade, the Technical Committee unpaused the share withdrawals and restored the full functionality of XYK liquidity mining.

## The vulnerability

The root cause of the vulnerability was the missing validation of the `AssetPair` provided by the user. In XYK liquidity mining, the `AssetPair` is used to derive the `amm_pool_id`, which identifies the AMM pool and determines which LP shares to unlock.

## The fix

We added a cross-check between the `amm_pool_id` derived from the `AssetPair` and the `amm_pool_id` saved in the `deposit`.

```rust
ensure!(amm_pool_id == deposit.amm_pool_id, Error::<T, I>::AmmPoolIdMismatch);
```

https://github.com/galacticcouncil/hydration-node/commit/2fb7430d615c4c50a6905c8218b01649423714f7

### Economic assessment

At the time of the report, there were 2 XYK pools with farms running, this would make this attack possible to perform. The attacker would need to accrue "lower valued shares" from DOT<>MYTH pair and join LM to be able to extract "higher valued shares of DOT<>EWT". By doing so, he would lock these shares forever.

There is roughly 200k$ worth of DOT <> EWT in LM. We have calculated that an attacker would need to accrue roughly 40k$ worth of DOT <> MYTH to empty DOT <> EWT pool not considering the slippage and other problems attacker would face with low liquidity pools, it is safe to say the total NET extracted value would be under 200k$.

As such, minimum payout for “Critical” issue is 20k$ under our Immunefi bug bounty programme paid out in HDX with 7 day EMA price of 0.0088

#27 Immunefi report payout - Malicious users will steal LP shares cross‑pool from liquidity‑mining depositors