bughuntoor - Users can front-run calls to change_gauge_weight in order to acquire more weight for their gauge

[sherlock-admin2]

bughuntoor

medium

Users can front-run calls to change_gauge_weight in order to acquire more weight for their gauge

Summary

Users can gain extra weight for their gauge by front-running change_gauge_weight

Vulnerability Detail

It can be expected that in some cases calls will be made to change_gauge_weight to increase or decrease a gauge's weight. The problem is users can be monitoring the mempool expecting such calls. Upon seeing such, any people who have voted for said gauge can just remove their vote prior to change_gauge_weight. Once it executes, they can vote again for their gauge, increasing its weight more than it was expected to be:
Example:

1. Gauge has 1 user who has voted and contributed for 10_000 weight
2. They see an admin calling change_gauge_weight with value 15_000.
3. User front-runs it and removes all their weight. Gauge weight is now 0.
4. Admin function executes. Gauge weight is now 15_000
5. User votes once again for the gauge for the same initial 10_000 weight. Gauge weight is now 25_000.

Gauge weight was supposed to be changed from 10_000 to 15_000, but due to the user front-running, gauge weight is now 25_000

Impact

Accruing extra voting power

Code Snippet

https://github.com/sherlock-audit/2023-11-convergence/blob/main/sherlock-cvg/contracts/Locking/GaugeController.vy#L569

Tool used

Manual Review

Recommendation

Instead of having a set function, use increase/ decrease methods.

Duplicate of #122