59742 sc high user funds get stucked in the contract when validators exits

Submitted on Nov 15th 2025 at 12:18:00 UTC by @danvinci_20 for Audit Comp | Vechain | Stargate Hayabusa

• Report ID: #59742

• Report Type: Smart Contract

• Report severity: High

• Target: https://github.com/immunefi-team/audit-comp-vechain-stargate-hayabusa/tree/main/packages/contracts/contracts/Stargate.sol

• Impacts:

  • Permanent freezing of funds

Description

Summary

The system decreases a user’s effective stake when they request a delegation exit and then decreases it again when they later call unstake() if the validator has already exited.

Because the validator is already in an exited state, the second decrease is performed using a later period index, causing _updatePeriodEffectiveStake() to underflow during:

updatedValue = currentValue - effectiveStake;

This results in a panic(0x11) arithmetic underflow, reverting unstake(). Since unstake() is the only mechanism for the user to retrieve their staked VET, the user’s funds become permanently stuck in the Stargate contract, with no recovery path.

Vulnerability Details

Relevant Code Paths

• When requestDelegationExit() is called, the contract immediately reduces the user's effective stake:

_updatePeriodEffectiveStake(
    $, 
    delegation.validator, 
    _tokenId, 
    completedPeriods + 2, 
    false
);

• Later, if the validator exits before the user calls unstake(), the unstake() function performs another decrease:

if (
    currentValidatorStatus == VALIDATOR_STATUS_EXITED ||
    delegation.status == DelegationStatus.PENDING
) {
    (, , , uint32 oldCompletedPeriods) =
        $.protocolStakerContract.getValidationPeriodDetails(delegation.validator);

    _updatePeriodEffectiveStake(
        $,
        delegation.validator,
        _tokenId,
        oldCompletedPeriods + 2,
        false // decrease again
    );
}

• Inside _updatePeriodEffectiveStake the underflow occurs:

uint256 updatedValue = _isIncrease
    ? currentValue + effectiveStake
    : currentValue - effectiveStake;  // underflows on second decrease

Because the second decrease subtracts the same effectiveStake from a smaller currentValue, the result becomes negative, causing a panic(0x11). This reverts the unstake() call entirely.

As a result, the user can never unstake or retrieve their VET, leaving their funds permanently stuck inside the Stargate contract.

Recommendation

Guard to ensure effective stake is only decreased once per delegation lifecycle and avoid trying to reduce effective stake for periods when there are no stakers.

Proof of Concept

Test showing the revert (add this test to Delegation.test.ts and run: yarn hardhat test --network vechain_solo test/integration/Delegation.test.ts)

it.only("user funds get stucked in the contract", async () => {
    const paramsKey = "0x00000000000064656c656761746f722d636f6e74726163742d61646472657373";
    const stargateAddress = await protocolParamsContract.get(paramsKey);
    const expectedParamsVal = BigInt(await stargateContract.getAddress());
    expect(stargateAddress).to.equal(expectedParamsVal);

    const validatorAddress = await protocolStakerContract.firstActive();
    expect(compareAddresses(validatorAddress, deployer.address)).to.be.true;

    const [leaderGroupSize, queuedValidators] =
        await protocolStakerContract.getValidationsNum();
    expect(leaderGroupSize).to.equal(1);
    expect(queuedValidators).to.equal(0);


    //staking the token here 
    const levelId = 1;
    const levelSpec = await stargateNFTContract.getLevel(levelId);
    const levelVetAmountRequired = levelSpec.vetAmountRequiredToStake;

    // Stake an NFT of level 1
    const stakeTx = await stargateContract
        .connect(user)
        .stake(levelId, { value: levelVetAmountRequired });
    await stakeTx.wait();
    log("\n🎉 Correctly staked an NFT of level", levelId);

    // Assert that user1 is the owner of the NFT, and the NFT is under the maturity period
    const tokenId = await stargateNFTContract.getCurrentTokenId();
    expect(await stargateNFTContract.ownerOf(tokenId)).to.equal(user.address);
    expect(await stargateNFTContract.isUnderMaturityPeriod(tokenId)).to.be.true;

    // Fast-forward until the NFT is mature
    await mineBlocks(Number(levelSpec.maturityBlocks));
    log("\n🚀 Fast-forwarded", Number(levelSpec.maturityBlocks), "blocks to mature the NFT");

    // Assert that the NFT is mature, so it can be delegated
    expect(await stargateNFTContract.isUnderMaturityPeriod(tokenId)).to.be.false;



    //new validator enters the staker
    const newValidator = (await ethers.getSigners())[5];
    const addValidatorTx = await protocolStakerContract.connect(newValidator).addValidation(newValidator.address, 12, {
            value: ethers.parseEther("25000000"),
        });
    await addValidatorTx.wait();
    log("\n🎉 Correctly added a new validator to the protocol");



    // Stargate <> ProtocolStaker - delegate the NFT to the validator
    const delegateTx = await stargateContract.connect(user).delegate(tokenId, newValidator.address);
    await delegateTx.wait();
    console.log("\n🎉 Correctly delegated the NFT to validator", newValidator.address);

    let delegation = await stargateContract.getDelegationDetails(tokenId);
    let [start,] = await protocolStakerContract.getDelegationPeriodDetails(delegation.delegationId);
    console.log("start period of delegation: ", start);

    let [period,startBlock,,completedPeriods] = await protocolStakerContract.getValidationPeriodDetails(newValidator.address);
    console.log("completedPeriods Before: ", completedPeriods);

    await fastForwardValidatorPeriods(
        Number(period),
        Number(startBlock),
        5
    );

    [,,,completedPeriods] = await protocolStakerContract.getValidationPeriodDetails(newValidator.address);
    console.log("completedPeriods Now: ", completedPeriods);


    const requestExitTx = await stargateContract.connect(user).requestDelegationExit(tokenId);
    await requestExitTx.wait();
    console.log("\n🎉 correctly request exit");

    delegation = await stargateContract.getDelegationDetails(tokenId);
    console.log("end period of delegation: ", delegation.endPeriod)

    await protocolStakerContract.connect(newValidator).signalExit(newValidator.address);


    let [,,exitBlock,] = await protocolStakerContract.getValidationPeriodDetails(newValidator.address);
    console.log("endPeriod of Validator: ", exitBlock);

    await fastForwardValidatorPeriods(
        Number(period),
        Number(startBlock),
        3
    );

     let [,,,,status,] = await protocolStakerContract.getValidation(newValidator.address);
    console.log("status is 3 showing exit: ", status);


    //now the user who delegated wants to exit unstake but gets a revert
    await expect(
        stargateContract.connect(user).unstake(tokenId)
    ).to.be.revertedWithPanic(0x11);
});

Output observed:

🎉 Correctly delegated the NFT to validator 0x61E7d0c2B25706bE3485980F39A3a994A8207aCf
start period of delegation:  1n
completedPeriods Before:  0n
completedPeriods Now:  5n

🎉 correctly request exit
end period of delegation:  6n
endPeriod of Validator:  120n
status is 3 showing exit:  3n
    ✔ user funds get stucked in the contract (6211ms)