Claiming outstanding utility tokens from `vMaia` vault DoS on `pbHermes<>bHermes` conversion rate > 1

mediumCode4rena

Lines of code

https://github.com/code-423n4/2023-05-maia/blob/54a45beb1428d85999da3f721f923cbf36ee3d35/src/maia/tokens/ERC4626PartnerManager.sol#L215-L229 https://github.com/code-423n4/2023-05-maia/blob/54a45beb1428d85999da3f721f923cbf36ee3d35/src/maia/vMaia.sol#L66-L88

Vulnerability details

Impact

Once a user deposits Maia ERC-20 tokens into the vMaia ERC-4626 vault, he is eligible to claim 3 kinds of utility tokens, bHermes Weight & Governance and Maia Governance (pbHermes, partner governance), via the ERC4626PartnerManager.claimOutstanding() method (ERC4626PartnerManager is base of vMaia contract).
The conversion rate between the utility tokens and vMaia tokens minted on deposit can be increased (and only increased) by the contract owner via the ERC4626PartnerManager.increaseConversionRate(...) method.

However, the checkWeight, checkGovernance & checkPartnerGovernance modifiers in the vMaia contract do not account for this conversion rate and therefore implicity only allow a conversion rate of 1.

As a consequence, as soon as the conversion rate is increased to > 1, a call to ERC4626PartnerManager.claimOutstanding() will inevitably revert due to subsequent calls to the above modifiers. Since the conversion rate can only be increased and the vMaia vault contract is not upgradeable, the claimOutstanding() method is subject to permanent DoS.
Of course, the user can still claim a reduced amount of utility tokens (according to a conversion rate of 1) via the PartnerUtilityManager.claimMultipleAmounts(...) method (PartnerUtilityManager is base of ERC4626PartnerManager contract), but this still implies a loss of assets for the user since not all utility tokens he is eligible for can be claimed. Furthermore, this workaround doesn't help when the user is a contract which implemented a call to the claimOutstanding() method.

Proof of Concept

The following PoC demonstrates the above DoS when trying to claim the utility tokens with increased conversion rate, just apply the diff below and run the test cases with forge test -vv --match-test testDepositMaia:

diff
diff --git a/test/maia/vMaiaTest.t.sol b/test/maia/vMaiaTest.t.sol
index 6efabc5..499abb6 100644
--- a/test/maia/vMaiaTest.t.sol
+++ b/test/maia/vMaiaTest.t.sol
@@ -7,9 +7,11 @@ import {SafeTransferLib} from "solady/utils/SafeTransferLib.sol";

 import {vMaia, PartnerManagerFactory, ERC20} from "@maia/vMaia.sol";
 import {IBaseVault} from "@maia/interfaces/IBaseVault.sol";
+import {IERC4626PartnerManager} from "@maia/interfaces/IERC4626PartnerManager.sol";
 import {MockVault} from "./mock/MockVault.t.sol";

 import {bHermes} from "@hermes/bHermes.sol";
+import {IUtilityManager} from "@hermes/interfaces/IUtilityManager.sol";

 import {DateTimeLib} from "solady/utils/DateTimeLib.sol";

@@ -47,7 +49,7 @@ contract vMaiaTest is DSTestPlus {
             "vMAIA",
             address(bhermes),
             address(vault),
-            address(0)
+            address(this) // set owner to allow call to 'increaseConversionRate'
         );
     }

@@ -86,6 +88,33 @@ contract vMaiaTest is DSTestPlus {
         assertEq(vmaia.balanceOf(address(this)), amount);
     }

+    function testDepositMaiaClaimDoS() public {
+        testDepositMaia();
+
+        // increase 'pbHermes<>bHermes' conversion rate
+        vmaia.increaseConversionRate(bHermesRate * 2);
+
+        // claim utility tokens DoS
+        hevm.expectRevert(IUtilityManager.InsufficientShares.selector);
+        vmaia.claimOutstanding();
+
+        // cannot undo conversion rate -> claimOutstanding() method is broken forever
+        hevm.expectRevert(IERC4626PartnerManager.InvalidRate.selector);
+        vmaia.increaseConversionRate(bHermesRate);
+    }
+
+    function testDepositMaiaClaimSuccess() public {
+        testDepositMaia();
+
+        vmaia.claimOutstanding();
+
+        // got utility tokens as expected
+        assertGt(vmaia.bHermesToken().gaugeWeight().balanceOf(address(this)), 0);
+        assertGt(vmaia.bHermesToken().governance().balanceOf(address(this)), 0);
+        assertGt(vmaia.partnerGovernance().balanceOf(address(this)), 0);
+    }
+
+
     function testDepositMaiaAmountFail() public {
         assertEq(vmaia.bHermesRate(), bHermesRate);

Tools Used

VS Code, Foundry

Recommended Mitigation Steps

Simply remove the incorrect checkWeight, checkGovernance & checkPartnerGovernance modifiers from the vMaia contract, since the correct modifiers, which account for the conversion rate, are already implemented in the ERC4626PartnerManager contract.

diff
diff --git a/src/maia/vMaia.sol b/src/maia/vMaia.sol
index 3aa70cf..5ee6f66 100644
--- a/src/maia/vMaia.sol
+++ b/src/maia/vMaia.sol
@@ -59,34 +59,6 @@ contract vMaia is ERC4626PartnerManager {
         currentMonth = DateTimeLib.getMonth(block.timestamp);
     }

-    /*///////////////////////////////////////////////////////////////
-                            MODIFIERS
-    //////////////////////////////////////////////////////////////*/
-
-    /// @dev Checks available weight allows for the call.
-    modifier checkWeight(uint256 amount) virtual override {
-        if (balanceOf[msg.sender] < amount + userClaimedWeight[msg.sender]) {
-            revert InsufficientShares();
-        }
-        _;
-    }
-
-    /// @dev Checks available governance allows for the call.
-    modifier checkGovernance(uint256 amount) virtual override {
-        if (balanceOf[msg.sender] < amount + userClaimedGovernance[msg.sender]) {
-            revert InsufficientShares();
-        }
-        _;
-    }
-
-    /// @dev Checks available partner governance allows for the call.
-    modifier checkPartnerGovernance(uint256 amount) virtual override {
-        if (balanceOf[msg.sender] < amount + userClaimedPartnerGovernance[msg.sender]) {
-            revert InsufficientShares();
-        }
-        _;
-    }
-
     /// @dev Boost can't be claimed; does not fail. It is all used by the partner vault.
     function claimBoost(uint256 amount) public override {}