Submitted by juancito, also found by falconhoof, gkrastenov, memforvik, 0xAsen, jasonxiale, 0x3b, 0xpiken, Ward, Limbooo, israeladelaja, 0xPluto, t0x1c, a3yip6, PENGUN, haxatron, miaowu, Myrault, b0g0, linmiaomiao, nonseodion, 0xAlix2 (1, 2), and y4y
An adversary can prevent the creation of setContract and websiteUpdate proposals by creating a poisonous proposal with the same ballot name + _confirm. This attack can be performed repeatedly every few days (when the voting period ends).
Affected proposals:
This is especially worrisome for the setContract proposals, as it prevents changing the price feed contracts, which are used for USDS borrowing and liquidations.
Note: This Impact fits into the Attack Ideas: Any issue that would prevent the DAO from functioning correctly.
setContract and websiteUpdate proposals are executed in multiple steps.
Heres the process for changing the Price Feed 1, as an example:
The problem is that there is a check in _possiblyCreateProposal() that can be exploited:
Proposals.sol#L103
This check is intended to prevent creating new proposals if there is a pending confirmation proposal being voted for the same change, but an adversary can use it to create a proposal  with a ballot name setContract:priceFeed1_confirm, by setting priceFeed1_confirm as the contract name.
If someone tries to create a legit priceFeed1 proposal later, it will revert, leading to a DOS.
This holds for all proposals mentioned in the Impact section.
Given the current implementation, the most straightforward fix would be to prevent the creation of proposals with ballot names ending in _confirm for proposals that need a confirmation.
This would mean checking the contractName in proposeSetContractAddress(), and the newWebsiteURL in proposeWebsiteUpdate().
But, as a recommendation, I would suggest refactoring createConfirmationProposal()  to pass a confirmation parameter to _possiblyCreateProposal(), so that confirmation proposals dont rely on the ballot name.
othernet-global (Salty.IO) confirmed and commented:
Picodes (Judge) commented:
Note: For full discussion, see here.
Status: Mitigation confirmed. Full details in reports from 0xpiken, zzebra83, and t0x1c.
