How Does Euler Finance Work? Permissionless Lending Explained

Euler Finance is a DeFi lending protocol that allows almost any ERC-20 token to be listed as a lending market permissionlessly, using a tiered risk classification system to manage the wide range of asset quality that comes with open listings.

Most major lending markets, like Aave or Compound, list assets only after a governance vote approves specific risk parameters for each one — a deliberately slow, curated process meant to keep low-quality or manipulable tokens out of the pool. Euler took a different approach: let the market list assets permissionlessly, and use a risk-tiering framework to contain the fallout if a lower-quality asset misbehaves.

The permissionless listing model

On Euler, anyone can create a lending market for an ERC-20 token without waiting for a governance proposal, similar in spirit to how anyone can create a trading pair on a permissionless DEX. This dramatically expands the range of assets that can be borrowed or lent compared to curated markets, letting long-tail tokens access lending liquidity that a governance-gated protocol would likely never approve.

The obvious risk is that permissionless listing opens the door to thinly traded, easily manipulated, or outright malicious tokens being used as collateral. Euler's design addresses this primarily through tiering rather than gatekeeping who can list.

Risk-tiered asset classification

Euler groups listed assets into tiers reflecting their risk level, which in turn determines how they can be used within the protocol:

• Isolation tier — newly listed or higher-risk assets can typically only be borrowed in isolation, meaning they can't be combined with other collateral in the same borrowing position, containing the blast radius if that specific asset is compromised or manipulated.
• Cross tier — more established assets can be used more flexibly across positions once they've demonstrated sufficient liquidity and stability.
• Collateral tier — the most reliable, deeply liquid assets can be used as collateral to borrow other assets, reflecting the highest level of trust in the tiering system.

This tiering means a newly listed, thinly traded token can still access lending markets, but any risk it introduces is largely walled off from the rest of the protocol's liquidity rather than threatening the whole system.

Permissionless vs. curated listing models

	Permissionless (Euler-style)	Curated (Aave/Compound-style)
Who can list an asset	Anyone	Requires governance approval
Speed to market	Immediate	Can take weeks to months
Asset quality control	Risk tiers contain exposure	Vetted before listing
Long-tail asset access	Broad	Limited to approved assets
Systemic risk if an asset fails	Contained by isolation tiering	Lower baseline risk, but slower innovation

The 2023 exploit and its lessons

Euler suffered a major exploit in March 2023 involving a flaw in its donation and liquidation logic, resulting in a significant loss of funds before most of it was ultimately recovered through negotiation with the attacker. The episode is a useful reminder that even well-designed risk-tiering frameworks don't eliminate smart contract risk — a permissionless, flexible protocol has more surface area for subtle bugs to hide in, and its safety ultimately depends on the quality of its audits and the maturity of its code, not just its risk model on paper. Euler subsequently relaunched with a rebuilt codebase and additional audits.

What this means for users

Permissionless listing gives users access to a much wider range of borrowable and lendable assets than curated protocols, but it also means the burden of due diligence shifts more toward the individual user — you need to understand which tier an asset sits in and what that implies about its risk, rather than assuming governance has already vetted it for you. Compare Euler's current TVL, supported assets, and audit history against other markets on our DeFi protocol rankings page, and read our broader DeFi lending guide if you're new to how these markets function.

Bottom line

Euler Finance's permissionless listing and risk-tiering model trades the slower, curated safety of protocols like Aave for much broader asset access, containing — but not eliminating — the risk that comes with letting anyone list a lending market. Its 2023 exploit is a reminder that flexible, permissionless design demands even more scrutiny of the underlying code, not less.