The OWASP Smart Contract Top 10 - 2026
The ten most consequential smart contract risks of 2026, mapped to real 2025 incidents from the SCH hack database. Each category includes vulnerable vs secure code, prevention checklists, detection tools, and a candid AI-vs-human auditor analysis.
The Top 10 (2026)
Ranked by a combination of practitioner survey, 2025 incident frequency, and total dollar loss.
Access Control Vulnerabilities
Improper access control describes any situation where a smart contract does not rigorously enforce who may invoke privileged behavior, under which conditions, and with which parameters.
Business Logic Vulnerabilities
Business logic vulnerabilities describe any situation where a smart contract's intended economic or functional behavior can be subverted even though individual low-level checks are correct. These are design flaws in how system rules, incentives, and state transitions are modeled, distinct from low-level bugs like overflow or reentrancy.
Price Oracle Manipulation
Price oracle manipulation describes any situation where a smart contract relies on price or valuation data that can be directly or indirectly influenced by an attacker, causing the protocol to make decisions based on incorrect values.
Flash Loan-Facilitated Attacks
Flash loan-facilitated attacks describe exploits where an attacker uses uncollateralized, same-transaction borrowing to amplify underlying vulnerabilities (logic, pricing, or arithmetic) into large drains by executing complex multi-step sequences in a single transaction.
Lack of Input Validation
Lack of input validation describes any situation where a smart contract processes external data - function parameters, calldata, cross-chain messages, or signed payloads - without rigorously enforcing that the data is well-formed, within expected bounds, and authorized for the intended operation.
Unchecked External Calls
Unchecked external calls describe any situation where a smart contract invokes another contract or address without fully accounting for the callee's behavior, return value, or reentrancy potential.
Arithmetic Errors (Rounding & Precision)
Arithmetic errors (rounding and precision loss) describe any situation where a smart contract performs integer-based calculations that produce incorrect or exploitable results due to truncation, scaling, or unit conversion.
Reentrancy Attacks
Reentrancy describes any situation where a smart contract performs an external call (to another contract or address), and the callee can call back into the original contract before the first invocation has completed, allowing repeated withdrawals or state changes from outdated views of contract state.
Integer Overflow and Underflow
Integer overflow and underflow describe situations where arithmetic operations produce values outside the representable range of the operand type.
Proxy & Upgradeability Vulnerabilities
Proxy and upgradeability vulnerabilities describe any situation where a smart contract uses an upgradeable architecture (proxy, beacon, or implementation-swapping pattern) and the upgrade path, initialization, or admin controls are misdesigned or misconfigured.
What changed: 2025 → 2026
OWASP made four major changes for 2026. Reentrancy fell three places, Business Logic was promoted to #2, Proxy & Upgradeability is brand new, and Insecure Randomness + DoS were dropped from the top ten.
| # | 2025 | 2026 | Delta |
|---|---|---|---|
| 1 | Access Control | Access Control | held |
| 2 | Price Oracle Manipulation | Business Logic | Business Logic ↑ from #3 |
| 3 | Logic Errors | Price Oracle Manipulation | Oracle ↓ from #2 |
| 4 | Lack of Input Validation | Flash Loan-Facilitated Attacks | Flash Loan ↑ from #7 |
| 5 | Reentrancy Attacks | Lack of Input Validation | Reentrancy ↓ to #8 |
| 6 | Unchecked External Calls | Unchecked External Calls | held |
| 7 | Flash Loan Attacks | Arithmetic Errors (Rounding & Precision) | SC07 reframed |
| 8 | Integer Overflow / Underflow | Reentrancy Attacks | Reentrancy moved here |
| 9 | Insecure Randomness | Integer Overflow / Underflow | Randomness removed |
| 10 | Denial of Service | Proxy & Upgradeability NEW | DoS removed |
AI vs human auditor detection - by category
SCH analysis of how 2026 frontier LLM auditors compare against senior human auditors for each OWASP category. Based on EVMbench, Cecuro, and CredShields benchmarks plus SCH editorial estimates. Not an OWASP-authored table - see methodology below.
| Category | AI auditor | Human auditor | Gap |
|---|---|---|---|
| SC01 Access Control | 17 pts | ||
| SC02 Business Logic | 47 pts | ||
| SC03 Oracle Manipulation | 34 pts | ||
| SC04 Flash Loan Attacks | 38 pts | ||
| SC05 Input Validation | 9 pts | ||
| SC06 External Calls | 13 pts | ||
| SC07 Arithmetic Errors | 22 pts | ||
| SC08 Reentrancy | 2 pts | ||
| SC09 Integer Overflow | 3 pts | ||
| SC10 Proxy & Upgradeability | 21 pts |
Takeaway: AI auditors have effectively closed the gap on reentrancy and integer overflow because tooling is mature and training data is dense. The widest gaps - business logic, oracle manipulation, flash-loan composition - require multi-step economic reasoning, which is still where senior human auditors win.
Methodology & sources
OWASP-authored vs SCH editorial
The category names, ranks, official descriptions, and 2025 incident citations on this hub are sourced from the OWASP Smart Contract Security project under CC BY-NC-SA 4.0. AI-vs-human detection rates, code examples, prevention checklists in the SCH voice, and the cross-references to SCH attack pages are SCH editorial. We mark this distinction explicitly so the page does not misrepresent OWASP as endorsing material we authored.
The $905.4M / 122 incidents number
OWASP's 2026 ranking is built on 122 deduplicated 2025 smart-contract incidents totalling ~$905.4M, sourced from CredShields' Web3HackHub, SlowMist, BlockSec, and DeFiHackLabs. This is the smart-contract-vector total - broader Web3 figures including phishing and CEX breaches are higher ($2.71B-$3.37B depending on aggregation). When other sites quote different totals, this is usually the reason.
No official OWASP PDF for 2026
OWASP publishes the Top 10 only as a MkDocs site. The PDFs referenced in some news coverage are third-party 2025 reports (Beosin, SlowMist, SolidityScan/CredShields, HackenProof, QuillAudits) that OWASP cites as data sources - not an OWASP-published PDF report.
Companion: Top 15 Web3 Attack Vectors
Alongside the Smart Contract Top 10, OWASP also publishes the Top 15 Web3 Attack Vectors (WA01-WA15) covering off-chain risks: multisig hijacking (Bybit $1.5B), supply-chain compromises, phishing, drainers, UI spoofing, and nation-state infiltration. Worth bookmarking separately - these are out of scope for the Top 10 but very much in scope for any audit engagement.
Learn the techniques behind every OWASP 2026 category
The SCH Smart Contract Hacking Course covers the exploit primitives, audit techniques, and tool workflows that map to every category in this list. Start free and see why what AI can't catch yet still defines the senior auditor.