50433 sc high validator list griefing unrestricted stakeonbehalf allows user asset freeze permanently

Submitted on Jul 24th 2025 at 15:24:20 UTC by @farman1094 for Attackathon | Plume Network

• Report ID: #50433

• Report Type: Smart Contract

• Report severity: High

• Target: https://github.com/immunefi-team/attackathon-plume-network/blob/main/plume/src/facets/StakingFacet.sol

• Impacts: Permanent freezing of funds

Description

Brief/Intro

The StakingFacet::stakeOnBehalf allows any user to stake on behalf of another user without requiring any form of authorization or consent. A malicious actor can grief victims by associating their accounts with a large number of validators, potentially causing the victim's funds to be locked permanently.

Vulnerability Details

The stakeOnBehalf function in the StakingFacet contract does not check if the staker has authorized the caller to stake on their behalf by any signature verification or delegation verification.

function stakeOnBehalf(uint16 validatorId, address staker) external payable returns (uint256) {
    if (staker == address(0)) {
        revert ZeroRecipientAddress();
    }

    uint256 stakeAmount = msg.value;

    // Perform all common staking setup for the beneficiary
    bool isNewStake = _performStakeSetup(staker, validatorId, stakeAmount);
...
}

As a result, any malicious address can use this function for any user, causing the user's userValidators array to be populated with many validators:

mapping(address => uint16[]) userValidators; // user => list of validators they've staked with

Functions like withdraw, restakeRewards, and restake later iterate over this array within _processMaturedCooldowns and _cleanupValidatorRelationships multiple times. When the victim address attempts to restake or withdraw tokens, the transaction can revert due to a denial-of-service (DoS) caused by exceeding the gas limit.

Impact Details

A malicious attacker can lock a victim’s staked funds and rewards by preventing them from calling withdraw, restakeRewards, or restake, as these functions will revert due to gas/iteration limits when iterating over an inflated userValidators array. This denial-of-service attack can result in permanent loss of access to funds, effectively freezing the victim’s assets within the staking contract.

Proof of Concept

1

Step

The attacker selects any user address ("victim") who has staked significant funds in the contract.

2

Step

The attacker calls the stakeOnBehalf function (which does not require any signature, approval, or explicit permission from the victim), passing the victim's address as the staker parameter and choosing a validator ID.

Relevant code:

function stakeOnBehalf(uint16 validatorId, address staker) external payable returns (uint256) {
    if (staker == address(0)) {
        revert ZeroRecipientAddress();
    }

    uint256 stakeAmount = msg.value;

    // Perform all common staking setup for the beneficiary
    bool isNewStake = _performStakeSetup(staker, validatorId, 
    ....
}

function _performStakeSetup(
  ...
    PlumeValidatorLogic.addStakerToValidator($, user, validatorId);
}

3

Step

Repeat the call many times, each time with a different validator ID. Each call appends that validator to the victim's userValidators mapping array:

mapping(address => uint16[]) userValidators; // user => list of validators they've staked with

4

Step

The victim’s userValidators array becomes bloated with many entries. When the victim later calls withdraw, restakeRewards, or restake, the contract iterates over the entire userValidators array.

Example iteration in _processMaturedCooldowns:

// StakingFacet::_processMaturedCooldowns
uint16[] memory userAssociatedValidators = $.userValidators[user];

for (uint256 i = 0; i < userAssociatedValidators.length; i++) {
    uint16 validatorId = userAssociatedValidators[i];
    PlumeStakingStorage.CooldownEntry memory cooldownEntry = $.userValidatorCooldowns[user][validatorId];
    ...
}

And again in _cleanupValidatorRelationships -> removeStakerFromAllValidators:

// PlumeValidatorLogic::removeStakerFromAllValidators

uint16[] memory userAssociatedValidators = $.userValidators[staker];

for (uint256 i = 0; i < userAssociatedValidators.length; i++) {
    uint16 validatorId = userAssociatedValidators[i];
    if ($.userValidatorStakes[staker][validatorId].staked == 0) {
        removeStakerFromValidator($, staker, validatorId);
    }
}

5

Step

With enough entries, these iterations hit gas limits and cause transactions to revert. As a result, the victim is unable to withdraw or restake their funds.

6

Step

The victim cannot recover or restake their funds, resulting in a permanent denial-of-service unless the contract logic is fixed.