Submitted by thekmj, also found by mert_eren, popular00, Eeyore, immeas, bart1e, 0xCiphky, ltyu, 0xbrett8571, deadrxsezzz, 0xDetermination, Tripathi, Team_Rocket, and pep7siup
https://github.com/code-423n4/2023-08-verwa/blob/main/src/GaugeController.sol#L127-L132 
https://github.com/code-423n4/2023-08-verwa/blob/main/src/GaugeController.sol#L213 
https://github.com/code-423n4/2023-08-verwa/blob/main/src/GaugeController.sol#L241
If governance removes a gauge for any (non-malicious) reason, a users voting power for that gauge will be completely lost.
The GaugeController is a solidity port of Curve DAOs Vyper implementation. Users are to vote for channeling incentives by using the vote_for_gauge_weights() function, and each user can fraction their voting power by $10000$ (that is, defined by BPS).
One modification from the original is that governance can now remove gauges, not allowing users to vote on it. However, any existing individual users voting power before removal is not reset. Since vote_for_gauge_weights() does not allow voting for removed gauges, the voting power is then forever lost.
Consider the following scenario:
It is worth noting that, even if Alice does not use 100% of her voting power on that particular gauge, she would still lose whatever percent vote placed in that pool, and her overall voting power was weakened by said percent.
Users can lose their voting power.
We provide the following POC to use on GaugeController tests.
Forge
The simplest way to mitigate this is to allow zero-weight votings on expired pools simply to remove the vote. Modify line 213 as follow:
https://github.com/code-423n4/2023-08-verwa/blob/main/src/GaugeController.sol#L213
The given POC can then be the test case to verify successful mitigation.
As a QA-based recommendation, the sponsor can also provide an external function to remove votes, and/or provide a function to vote for various pools in the same tx. This will allow users to channel their votes directly from removed pools to ongoing pools.
