Algorand Vulnerability ScannerCAUTION

Trail of Bits skills for security research, vulnerability detection, and audit workflows

The instruction file, verbatim from the audited commit — this is the text the model reads, and the surface the audit's instruction layer examines. Quoted here so you can judge it without cloning anything.

---
name: algorand-vulnerability-scanner
description: Scans Algorand smart contracts for 11 common vulnerabilities including rekeying attacks, unchecked transaction fees, missing field validations, and access control issues. Use when auditing Algorand projects (TEAL/PyTeal).
---

# Algorand Vulnerability Scanner

## 1. Purpose

Systematically scan Algorand smart contracts (TEAL and PyTeal) for platform-specific security vulnerabilities documented in Trail of Bits' "Not So Smart Contracts" database. This skill encodes 11 critical vulnerability patterns unique to Algorand's transaction model.

## 2. When to Use This Skill

- Auditing Algorand smart contracts (stateful applications or smart signatures)
- Reviewing TEAL assembly or PyTeal code
- Pre-audit security assessment of Algorand projects
- Validating fixes for reported Algorand vulnerabilities
- Training team on Algorand-specific security patterns

## 3. Platform Detection

### File Extensions & Indicators
- **TEAL files**: `.teal`
- **PyTeal files**: `.py` with PyTeal imports

### Language/Framework Markers
```python
# PyTeal indicators
from pyteal import *
from algosdk import *

# Common patterns
Txn, Gtxn, Global, InnerTxnBuilder
OnComplete, ApplicationCall, TxnType
@router.method, @Subroutine
```

### Project Structure
- `approval_program.py` / `clear_program.py`
- `contract.teal` / `signature.teal`
- References to Algorand SDK or Beaker framework

### Tool Support
- **Tealer**: Trail of Bits static analyzer for Algorand
- Installation: `uv tool install tealer` (ensure uv's tool bin dir is on PATH)
- Usage: `tealer contract.teal --detect all`

---

## 4. How This Skill Works

When invoked, I will:

1. **Search your codebase** for TEAL/PyTeal files
2. **Analyze each file** for the 11 vulnerability patterns
3. **Report findings** with file references and severity, above them a coverage table carrying a verdict for every pattern
4. **Provide fixes** for each identified issue
5. **Run Tealer** (if installed) for automated detection

---

## 5. Example Output

When vulnerabilities are found, you'll get a report like this:

```
=== ALGORAND VULNERABILITY SCAN RESULTS ===

Project: my-algorand-dapp
Files Scanned: 3 (.teal, .py)
Vulnerabilities Found: 2

Coverage: 11/11 patterns reported
 1 Rekeying Attack ................... found   approval.py:45
 2 Unchecked Transaction Fee ......... n/a     stateful app, fees paid by sender
 3 Closing Account ................... clear   Assert(Txn.close_remainder_to() == Global.zero_address())
 ... one row per pattern, all 11 present ...

---

[CRITICAL] Rekeying Attack
File: contracts/approval.py:45
Pattern: Missing RekeyTo validation

Code:
    If(Txn.type_enum() == TxnType.Payment,
        Seq([
            # Missing: Assert(Txn.rekey_to() == Global.zero_address())
            App.globalPut(Bytes("balance"), balance + Txn.amount()),
            Approve()
        ])
    )

Issue: The contract doesn't validate the RekeyTo field, allowing attackers
to change account authorization and bypass restrictions.
```

---

## 6. Vulnerability Patterns (11 Patterns)

I check for 11 critical vulnerability patterns unique to Algorand. For detailed detection patterns, code examples, mitigations, and testing strategies, see [VULNERABILITY_PATTERNS.md](resources/VULNERABILITY_PATTERNS.md).

### Pattern Summary:

1. **Rekeying Attack** ⚠️ CRITICAL - Unchecked RekeyTo field
2. **Unchecked Transaction Fee** ⚠️ HIGH - Fee not validated in smart signatures
3. **Closing Account (CloseRemainderTo)** ⚠️ CRITICAL - Unchecked CloseRemainderTo drains the account
4. **Closing Asset (AssetCloseTo)** ⚠️ CRITICAL - Unchecked AssetCloseTo drains the asset holding
5. **Group Size Check** ⚠️ HIGH - No `Global.group_size()` validation on atomic groups
6. **Time-Based Replay Attack** ⚠️ MEDIUM - No lease or round-range bound
7. **Access Controls** ⚠️ CRITICAL - Update/delete and privileged calls unprotected
8. **Asset ID Verification** ⚠️ HIGH - Asset ID not validated in asset operations
9. **Denial of Service (Asset Opt-In)** ⚠️ MEDIUM - Push transfers strand on un-opted accounts
10. **Inner Transaction Fee** ⚠️ MEDIUM - Inner fee not explicitly set to 0
11. **Clear State Transaction** ⚠️ HIGH - Clear state program cannot reject, state left inconsistent

For complete vulnerability patterns with code examples, see [VULNERABILITY_PATTERNS.md](resources/VULNERABILITY_PATTERNS.md).

## 7. Scanning Workflow

### Step 1: Platform Identification
1. Confirm file extensions (`.teal`, `.py`)
2. Identify framework (PyTeal, Beaker, pure TEAL)
3. Determine contract type (stateful application vs smart signature)
4. Locate approval and clear state programs

### Step 2: Static Analysis with Tealer
```bash
# Run Tealer on contract
tealer contract.teal --detect all

# Or specific detectors
tealer contract.teal --detect unprotected-rekey,group-size-check,update-application-check
```

### Step 3: Manual Vulnerability Sweep
For each of the 11 vulnerabilities above:
1. Search for relevant transaction field usage
2. Verify validation logic exists
3. Check for bypass conditions
4. Validate inner transaction handling

### Step 4: Transaction Field Validation Matrix
Create checklist for all transaction types used:

**Payment Transactions**:
- [ ] RekeyTo validated
- [ ] CloseRemainderTo validated
- [ ] Fee validated (if smart signature)

**Asset Transfers**:
- [ ] Asset ID validated
- [ ] AssetCloseTo validated
- [ ] RekeyTo validated

**Application Calls**:
- [ ] OnComplete validated
- [ ] Access controls enforced
- [ ] Group size validated

**Inner Transactions**:
- [ ] Fee explicitly set to 0
- [ ] RekeyTo not user-controlled (Teal v6+)
- [ ] All fields validated

### Step 5: Group Transaction Analysis
For atomic transaction groups:
1. Validate `Global.group_size()` checks
2. Review absolute vs relative indexing
3. Check for replay protection (Lease field)
4. Verify OnComplete fields for ApplicationCalls in group

### Step 6: Access Control Review
- [ ] Cr

CAUTIONgrade B · trust 89/100 Install with care. The audit found things worth knowing before you trust its output.

What the source does

Filesystem

none-observed

Network

none-observed

Shell

none-observed

Dependencies

pinned

Secrets in source

none-found

Findings (2)

plugins/modern-python/hooks/shims/pip3

plugins/modern-python/hooks/shims/python3

Gates applied: no_behavioural_pass.

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