plamentsv / cpi-security
Trigger Pattern CPI flag detected (invoke/invoke_signed/CpiContext usage) - Inject Into Breadth agents, depth agents
CPI_SECURITY Skill
Trigger Pattern: CPI flag detected (invoke/invoke_signed/CpiContext usage)
Inject Into: Breadth agents, depth agents
Finding prefix:[CPI-N]
Rules referenced: S3, S5, R1, R4
For every Cross-Program Invocation (CPI) in the Solana program:
1. CPI Target Inventory
Enumerate ALL CPI calls:
| # | Location | CPI Type | Target Program | Target Instruction | Accounts Forwarded | Signers Forwarded |
|---|---|---|---|---|---|---|
| 1 | {file:line} | invoke/invoke_signed/CpiContext | {program_id} | {instruction} | {list} | {list} |
2. Target Program Validation
For each CPI call, verify the target program ID:
| CPI | Program ID Source | Hardcoded/Validated? | Spoofable? |
|---|---|---|---|
| {cpi} | {where program_id comes from} | Hardcoded constant / Validated against known / FROM USER INPUT | {if from input: CRITICAL finding} |
Attack (S3): If program ID comes from user input without validation, attacker substitutes a malicious program that mimics the expected interface but steals funds.
Defense: Always validate program ID against a hardcoded constant or well-known program address.
3. Signer Privilege Tracing
For each CPI that forwards signers:
| CPI | Signer Source | Privilege Level | Should Forward? | Over-Privileged? |
|---|---|---|---|---|
| {cpi} | {PDA / user wallet / authority} | {what the signer can do in target} | YES/NO | {if forwarding more privilege than needed} |
Attack: Forwarding user's wallet as signer to a CPI target that uses it for unintended operations.
Pattern: PDA signers via invoke_signed are safe (program-controlled). User wallet forwarding needs careful scoping.
4. Account Reload Audit (S5 - CRITICAL)
For each CPI call, check what accounts are read AFTER the CPI returns:
| CPI | Accounts Modified by Target | Read After CPI? | reload() Called? | Owner Re-checked? |
|---|---|---|---|---|
| {cpi} | {list accounts CPI can modify} | YES/NO | YES/NO | YES/NO |
Attack (S5): CPI target modifies account data. Caller reads stale cached data without reload().
CRITICAL: Anchor's reload() refreshes data but does NOT re-verify the account owner. A CPI target could assign the account to a different program. After reload(), the data is fresh but the owner may have changed.
Full defense: After CPI, both reload() AND re-check account.owner.
5. Lamport Balance Conservation
For each CPI that transfers SOL:
| CPI | Expected Lamport Change | Actual Change Verified? | Drain Risk? |
|---|---|---|---|
| {cpi} | {expected delta} | YES/NO | {if NO: CPI could drain more than expected} |
Attack: CPI target drains more lamports than expected from accounts owned by the caller's program.
Defense: Check lamport balances before and after CPI; verify delta matches expected amount.
6. Account Owner Check Post-CPI
For each CPI that could modify account ownership:
| CPI | Can Target Call system_program::assign? | Owner Checked After CPI? | Risk |
|---|---|---|---|
| {cpi} | YES/NO | YES/NO | {if YES and NO: account hijacking} |
Attack: CPI target uses system_program::assign to change account owner to attacker-controlled program. Caller continues using the account assuming it's still owned by its program.
7. CPI Depth Analysis
For each code path with nested CPIs:
| Entry Point | CPI Chain | Max Depth | CU Cost Estimate | Risk |
|---|---|---|---|---|
| {instruction} | {A → B → C} | {depth} | {estimate} | {CU exhaustion?} |
Solana limit: CPI depth capped at 4 levels. Check if deep chains approach this limit.
Finding Template
**ID**: [CPI-N]
**Severity**: [based on impact: fund theft via program spoofing = Critical, stale data = High]
**Step Execution**: ✓1,2,3,4,5,6,7 | ✗(reasons) | ?(uncertain)
**Rules Applied**: [S3:✓, S5:✓, R1:✓, R4:✓/✗]
**Location**: program/src/{file}.rs:LineN
**Title**: [CPI issue type] in [instruction] enables [attack]
**Description**: [Specific CPI vulnerability with call chain trace]
**Impact**: [Fund theft / state corruption / privilege escalation]Step Execution Checklist (MANDATORY)
| Section | Required | Completed? | Notes |
|---|---|---|---|
| 1. CPI Target Inventory | YES | ✓/✗/? | For every CPI |
| 2. Target Program Validation | YES | ✓/✗/? | For every CPI |
| 3. Signer Privilege Tracing | YES | ✓/✗/? | For every CPI with signers |
| 4. Account Reload Audit | YES | ✓/✗/? | CRITICAL - most common CPI bug |
| 5. Lamport Balance Conservation | IF SOL transfers | ✓/✗(N/A)/? | |
| 6. Account Owner Check Post-CPI | YES | ✓/✗/? | assign attack prevention |
| 7. CPI Depth Analysis | IF nested CPIs | ✓/✗(N/A)/? | CU exhaustion risk |