The security audits for the Yo Protocol, conducted by Hunter Security, Offbeat Security, and Spearbit, initially brought good news: no critical or high-severity vulnerabilities were identified in its code. However, a deeper analysis, informed by the protocol's own documentation on docs.yo.xyz and architectural overview on deepwiki.com/yoprotocol/core, reveals significant potential vulnerabilities. These risks are particularly concerning given Yo Protocol's pivotal role as a multi-chain yield optimizer deeply integrated with numerous other DeFi protocols. This widespread integration amplifies the potential impact of any flaw, making a comprehensive understanding of its security posture paramount for the entire blockchain ecosystem. This article, therefore, gains substantial importance, as it sheds light on risks that could have cascading effects across a significant portion of the DeFi landscape. If exploited in real-world use, these hidden risks could lead to substantial financial losses for users and the various integrated protocols alike.

While the Yo Protocol engaged external firms for its security audits, a closer look at the public presence of these auditors offers a point for consideration regarding transparency. Hunter Security, one of the auditing firms, notes in its report that security audit inquiries can be directed to their lead on X (formerly Twitter) at @georgehntr. However, at the time of this analysis, attempts to access this account reveal that "This account doesn't exist." While acknowledging and respecting the work of lead security researcher @deadrosesxyz, the absence of a verifiable public presence for a named founder or key contact of an auditing firm, especially for direct inquiries, can subtly detract from overall public credibility and transparency in the highly trust-dependent DeFi space. For a blockchain ecosystem that thrives on verifiable assurances, the public accessibility and consistent presence of audit teams are increasingly vital for fostering confidence.

Let's now dive into the often-overlooked vulnerabilities within the Yo Protocol itself and explore the crucial solutions needed to fortify its defenses.

Yo Protocol positions itself as a multi-chain yield optimizer, actively integrating with a diverse array of DeFi protocols to source yield, enable rebalancing, looping, lending, liquidity provision, and other critical functionalities. This extensive network of integrations showcases the technological trust placed in Yo Protocol to manage and route capital efficiently across the blockchain ecosystem.

Its integrations span several crucial categories:

• Yield Sources (Protocols Yo Routes Capital To for Optimized Yield): These are core integrations where Yo allocates user deposits to generate risk-adjusted returns, including major players like Aave (Umbrella), Aerodrome, Arcadia, Convex, Curve, Euler, Harvest, IPOR, Morpho, Pendle, Reserve, Tokemak, and Yearn. The inclusion of such prominent protocols underscores the significant trust placed in Yo Protocol's yield-routing capabilities.

With over 55 yield sources across more than 18 protocols, and a focus on non-custodial, automated yield with ERC-4626 standards for composability, Yo Protocol is clearly interwoven into the fabric of the DeFi ecosystem. This extensive web of integrations is precisely why a thorough security analysis of Yo Protocol is critical. Any vulnerability, especially those not immediately apparent from code audits, could have far-reaching implications, affecting not only Yo Protocol's direct users but also all the protocols and users interacting through these integrations.

The most critical overarching vulnerability is the extensive control granted to the vault operator, coupled with an authorization mechanism that doesn't verify if an authorized caller is allowed to send Ether (ETH) value along with a function call. The AuthUpgradeable contract, as described in the DeepWiki, "provides role-based access control throughout the protocol" and "ensures that only authorized addresses can perform privileged operations." This means if an attacker compromises any address that has been granted authorization to call any function through the manage() function (e.g., via phishing, malware, or a private key leak), they could exploit this privilege to drain the vault's entire ETH balance. Spearbit's review further highlighted that an operator can change the share-to-asset exchange rate at their discretion during fulfillRedeem(), reinforcing the significant power vested in these centralized roles. Furthermore, Spearbit identified that inflation griefing attacks are possible for initial depositors due to the default _decimalsOffset() not being overridden. While Yo Protocol acknowledged this primarily affects the very first user and is mitigated by private deployment scripts, it points to a design vulnerability in extreme conditions. The protocol's reliance on highly trusted operators who can "execute arbitrary calls with vault's assets" implies that the security of the entire system ultimately hinges on the impeccable security of these few operators. While the Yo Protocol documentation states it is "fully decentralized, meaning you’re always in control of your assets", this appears to refer to user custody rather than core protocol governance and operational control, which remains centralized in critical aspects.

These aren't hypothetical scenarios; platforms like rekt.news frequently report on such incidents. Consider the BTCTurk private key leak, which resulted in $55 million, then $51.7 million, being stolen. Or the Venus Protocol founder falling for a malicious Zoom link, leading to a $13 million loss. The Swissborg $41.5 million loss due to a trusted partner (Kiln) being "API-owned" further underscores the cascading risk when centralized control points are compromised.

It's crucial to document this behavior clearly in the code and external documentation, as highlighted in security reviews. Authorization must only be granted to highly trusted addresses. Furthermore, the protocol should consider implementing additional controls and restrictions to reduce these centralization risks over time as it matures, as recommended by security auditors. This includes potentially implementing multi-signature requirements or time-locks for critical operations, and implementing checks to ensure fulfillRedeem() only processes shares and assets in correct proportions.

The Yo Protocol's mechanism for updating underlying balances creates predictable arbitrage opportunities. This is primarily due to its system of updating the total market value across all chains approximately once per day through the onUnderlyingBalanceUpdate() function. The DeepWiki notes that the vault can "fetch and update underlying balances from an external oracle", and that it has "Pausability" in case of "significant balance discrepancies detected through oracle updates." This creates discrete jumps in asset valuation instead of smooth price changes, a point raised in all audit findings. Spearbit explicitly stated that onUnderlyingBalanceUpdate can be sandwiched, directly confirming earlier reports. Additionally, Spearbit found that depositors can exploit incorrect price ratios from yield gains to get more shares, where yield accrual between a redemption request and fulfillment can skew the total asset-to-share ratio, allowing new depositors to mint more shares than intended.

An attacker (or an MEV bot) can continuously monitor the blockchain mempool for these onUnderlyingBalanceUpdate() transactions. When they see a transaction that will increase the aggregated balance, they can front-run it with a large deposit into the vault at the current, lower price. Once the balance update completes (increasing the price), they can back-run with an instant redemption of their shares at the new, higher price, effectively capturing the yield increase that would have otherwise gone to legitimate long-term holders. While the profit per individual attack might be "bounded by the size of the yield 'jump'," consistent exploitation can significantly erode the yield for legitimate users and make the protocol less attractive over time. Yo Protocol has acknowledged this issue and stated they are using private RPCs to mitigate this specific sandwich attack vector.

This is a classic MEV attack vector. Rekt.news has highlighted how Coinbase lost $550K after an MEV bot exploited ERC-20 approvals to drain tokens, and Odin.Fun hemorrhaged $7 million through "basic AMM manipulation".

A key recommendation from audits is to ensure that the aggregatedUnderlyingBalances is always updated within the same transaction when funds are leaving the vault's balance. Additionally, given the complexity of handling jumps in accumulated rewards, the protocol should consider implementing a more gradual approach to updating underlying asset balances or adding cool-down periods before withdrawals to prevent sandwich attacks. Furthermore, for the specific issue of depositors exploiting incorrect price ratios, auditors recommend updating total shares and total assets to reflect reserved pending redemption amounts, as these assets are essentially locked in a predetermined ratio.

Seemingly minor accounting and rounding errors can lead to significant financial discrepancies.

• Total pending assets not accounting for fees: The totalPendingAssets variable is updated with the net asset amount (assets after fees) instead of the total amount including fees. This leads to an overestimation of the actually available balance, as identified in Hunter Security and Offbeat Security reviews. Spearbit further found that the results of pendingRedeemRequest() are misleading because they store the expected assetsWithFee without subtracting fees, and fees can change. Consequently, if a user initiates a large redemption, the system might believe more funds are available than truly exist, allowing other users to "jump the queue" and withdraw funds meant for the pending redemption, potentially causing a temporary liquidity crunch or a failed redemption for the initial user.

• Precision loss in fee calculations: Fees are calculated twice (once during request, again during withdrawal), which can introduce rounding errors and lead to small, unrecoverable "dust" amounts accumulating within the contract, as noted by Offbeat Security. While individually negligible, this trapped value could either be exploited by a clever attacker or simply represent unrecoverable funds for the protocol.

• Revert on zero totalSupply(): Spearbit also identified that onUnderlyingBalanceUpdate() could revert on totalSupply() of 0, making it impossible to call _pause() in such a scenario. While fixed in PR, it highlights a potential robustness issue related to the vault's underlying state.

The Bunni protocol's $8.4 million loss due to a "basic rounding bug" serves as a stark reminder that even seemingly minor precision issues can have catastrophic financial consequences in DeFi. Similarly, BetterBank lost $5 million due to a "simple incentive flaw" in its reward logic, demonstrating how mathematical miscalculations can quickly turn into catastrophic losses. The Cyfrin Solodit comprehensive database of smart contract vulnerabilities can be an invaluable resource for developers and auditors to study past exploits and prevent similar issues in their own protocols.

To address the first issue, totalPendingAssets should be increased by the assetsWithFee instead of just assets in the requestRedeem function, as recommended by auditors. For precision loss, the recommendation is to store the assetsWithFee amount instead of the fee-subtracted assets, and modify _withdraw() to handle fee calculations in a single place, ensuring consistent calculations and preventing dust accumulation. For misleading pendingRedeemRequest() results, auditors recommend either subtracting fees and adding a comment that fees can change, or explicitly locking in fees at the time of request.

Issues related to standard compliance and user control can lead to unexpected financial outcomes or operational friction. The DeepWiki highlights "ERC4626 Compliance" and "Asynchronous Redemption" as key features of the protocol.

• EIP-4626 non-compliance: The requestRedeem function does not fully comply with the EIP-4626 standard for redeem flows and previewWithdraw functions, as it does not support approvals or account for withdrawal fees, a point raised in both Hunter Security and Offbeat Security reports. Spearbit also highlighted that maxDeposit, maxMint, maxWithdraw, and maxRedeem functions should return 0 when the contract is paused to properly comply with ERC4626 paused state expectations.

• Inability to cancel withdrawal requests: Users cannot cancel their own pending redemption requests, as noted in the audit findings. This exposes users to market risk, as they might be forced to redeem at a significant loss if asset prices change unfavorably during the delay before fulfillment.

• Cancelled redemption shares returned to receiver instead of owner: When a redemption request is cancelled, the shares are returned to the receiver address specified in the original request, not necessarily the owner who initiated it. This was an informational finding from Offbeat Security and confirmed as a low-risk issue by Spearbit, noting that tokens may not be going to respective wallets. If the owner and receiver are different, this can lead to unintended transfers or disputes. If the receiver address is compromised or malicious, they could unjustly claim shares intended for the original owner.

• Informational Issues: Other minor but critical issues identified across audits include allowing address(0) as a receiver (which could lead to assets being permanently locked or burned), passing

External dApps or aggregators that integrate with Yo Protocol, expecting full EIP-4626 compliance, might receive incorrect previewWithdraw values (not accounting for fees) or be unable to execute certain approved redemption flows. This can lead to users being misled about the final withdrawal amount, causing financial disappointment, or hindering interoperability, limiting the protocol's adoption. A user stuck with an unfulfillable redemption due to adverse market changes faces direct financial loss, a significant user experience failure.

The protocol should override previewWithdraw() to accurately account for fees, or, if only asynchronous withdrawals are supported, follow EIP-7540 and revert, as recommended by security reviews. To improve user control, consider allowing users to cancel their own redeem requests or introducing a deadline parameter for redemptions. For cancelled redemptions, either implement owner tracking (though this requires significant architectural changes) or, at minimum, update code comments and external documentation to clearly reflect that shares return to the designated receiver. All typographical mistakes, non-critical issues, and centralization vulnerabilities enumerated in the informational findings should be addressed, including preventing address(0) as a receiver and ensuring correct use of msg.sender versus receiver. Additionally, the documentation in the yoprotocol/yield-server GitHub repository should replace the Anchor Protocol example with one from a currently successful and stable protocol to foster greater trust and confidence in the project's adherence to best practices and learning from past industry events. General code quality improvements like adding input validation sanity checks, addressing shadowed state variables, and improving documentation around trust assumptions and operator privileges are also vital, as suggested by Offbeat Security.

Beyond initial code audits, a robust bug bounty program is a cornerstone of continuous security in DeFi. The Yo Protocol has an active bug bounty program hosted on Immunefi, a leading Web3 security platform.

Currently, Yo Protocol offers a maximum bounty of $10,000 for critical smart contract vulnerabilities, with a minimum payout of $5,000. The reward calculation is stated as 10% of the funds directly affected, up to this $10,000 maximum. The program also requires Proof of Concept (PoC) and KYC information for payout processing. Yo Protocol employs a "Primacy of Impact" approach for critical and high-severity issues, encouraging researchers to report any in-scope impact regardless of affected assets.

However, when viewed through the lens of the rekt.news article "Cutting Corners", Yo Protocol's bug bounty structure raises significant concerns regarding incentive alignment. The article vividly describes how "exploitation now pays orders of magnitude more than disclosure" when bounties are capped too low. Protocols are depicted as "pinching pennies on security, then act shocked when someone finds the vulnerabilities they refused to pay for."

The "Cutting Corners" article highlights that the Immunefi CEO, Mitchell Amador, advocates for bounties around 10% of funds at risk to make disclosure more profitable than exploitation. For example, protecting $10 million should ideally involve a bounty of up to $1 million. Yo Protocol explicitly acknowledges "substantial financial losses" as a potential outcome from its vulnerabilities, such as a compromised operator key leading to the draining of the "vault's entire ETH balance." If the vault were to hold, for instance, $1 million in ETH, a 10% bounty would be $100,000. Yet, Yo Protocol's $10,000 cap for critical smart contract bugs means that even if a whitehat discovers a vulnerability capable of draining millions, their maximum reward would be fixed at this relatively low amount.

This discrepancy creates a misaligned incentive structure, as argued in the rekt.news article. The article points out that Cork Protocol (audited by Cantina)'s $100,000 bounty cap couldn't prevent a $12 million hack, demonstrating that a cap significantly below the funds at risk is an invitation for exploitation. Similarly, SuperRare's $730,000 loss was attributed to having no public bug bounty program. Given the potential for "substantial financial losses" in the Yo Protocol, a $10,000 maximum bounty might be insufficient to motivate top-tier security researchers to dedicate the extensive time and effort required to uncover complex vulnerabilities, especially when a malicious actor could potentially gain far more by exploiting them. This positions Yo Protocol among the platforms that rekt.news warns are "racing toward the bottom" with "discount security." The current structure, according to the rekt.news thesis, risks creating a "death spiral that benefits no one except malicious actors."

To genuinely align incentives and effectively safeguard user funds, Yo Protocol should significantly increase its maximum bug bounty payout for critical vulnerabilities. The bounty should reflect a more substantial percentage of the actual funds at risk, especially considering the "vault's entire ETH balance" could be compromised. Protocols like LayerZero ($15 million), MakerDAO/Sky ($10 million), and Wormhole ($5 million) set industry benchmarks by offering rewards that make disclosure unambiguously more profitable than exploitation, leading to stronger security outcomes. Revisiting this cap to be commensurate with the potential impact of vulnerabilities, rather than a fixed low amount, is crucial for fostering robust, continuous security. Lessons from GMX and KiloEx, which offered substantial recovery bounties after being hacked, reinforce that the funds are available—the choice lies in proactive prevention versus reactive damage control.

While code audits by reputable firms like Hunter Security, Offbeat Security, and Spearbit are a fundamental step in smart contract security, and the Yo Protocol has transparently shared its design on DeepWiki and official documentation, this case clearly demonstrates that they are just the beginning, especially for a protocol so deeply embedded in the DeFi landscape. The most critical vulnerabilities often lie beyond immediately exploitable code bugs, residing instead in centralized operational control, critical design choices, and subtle logic flaws. For a protocol that acts as a bridge and optimizer for numerous other platforms, ensuring robust measures against these risks is not just about Yo Protocol itself, but about safeguarding a significant segment of the blockchain ecosystem. This makes a comprehensive security strategy, beyond just fixing code bugs, crucial for the long-term security and trustworthiness of the Yo Protocol and, by extension, its many integrated partners.

For protocols seeking to go beyond basic audits and implement comprehensive, continuous security solutions, platforms like Sherlock offer advanced security suites, audit contests, and bug bounties powered by top security researchers. With a track record of finding over 1,500 critical vulnerabilities and securing over $100 billion in TVL, Sherlock provides solutions from early development to scaling, ensuring protocols are prepared for the threats ahead. By embracing a holistic approach to security, including rigorous design reviews, continuous monitoring, and community-driven bug bounties with properly aligned incentives, protocols can build truly resilient and trustworthy systems.

The ultimate goal of analyses like this is to contribute to a safer and more transparent blockchain ecosystem. We urge the Yo Protocol development team to provide regular updates to the community regarding the status of the issues identified in their audit reports and the steps being taken to address them. We wish the Yo Protocol every success in its journey towards achieving truly robust security for its users and its integrated partners.

Endnote from the On-chain Analyst:

This analysis represents a deep dive into the Yo Protocol's architecture and security posture, drawing on multiple sources and highlighting potential risks that extend beyond initial audit findings. The effort involved in synthesizing this information and drawing actionable conclusions is considerable. If you find this kind of detailed on-chain reporting valuable for understanding the true risks in the DeFi ecosystem, please consider supporting my work;

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