CONTRACT_UPGRADEABILITY Skill (Soroban)

Trigger Pattern: update_current_contract_wasm detected in codebase Inject Into: Breadth agents, depth-state-trace Finding prefix: [CU-N] Rules referenced: R6, R10, R12, R13

Soroban provides env.deployer().update_current_contract_wasm(new_wasm_hash) for in-place contract upgrades. This is more powerful than EVM proxy patterns — it directly replaces the executing contract's WASM bytecode without changing the contract address or storage. Unrestricted upgrade capability is an absolute control vector; the upgrade gate must be airtight.

1. Upgrade Access Control

Locate every call to update_current_contract_wasm and verify the auth gate:

Minimum requirement: The upgrade function MUST call require_auth() or require_auth_for_args() on a privileged address before calling update_current_contract_wasm.

Patterns to flag as insufficient:

• No auth check at all (anyone can upgrade)
• Auth check on a non-admin address (e.g., any token holder)
• Auth check after update_current_contract_wasm is called (too late — code already replaced)
• The privileged address is stored in Temporary storage (can be deleted/expired, unlocking upgrade for anyone)

Also check:

• Is the admin address itself protected from replacement without auth? (see Section 3)
• Can the upgrade function be called during initialization before admin is set? (init race)

2. Migration Safety

An upgrade replaces WASM but preserves ALL storage. If the new WASM has a different storage layout or new required keys, the upgrade function must handle migration:

Migration pattern check:

pub fn upgrade(env: Env, new_wasm_hash: BytesN<32>) {
    // Step 1: Auth gate
    let admin = env.storage().instance().get::<_, Address>(&DataKey::Admin).unwrap();
    admin.require_auth();
    // Step 2: Replace WASM
    env.deployer().update_current_contract_wasm(new_wasm_hash);
    // Step 3: Migrate storage (if needed)
    // env.storage().instance().set(&DataKey::NewField, &default_value);
}

Absence of migration: If the upgraded WASM accesses storage keys or uses different struct layouts than the currently-stored data, ALL post-upgrade operations will panic. This is effectively a self-inflicted DoS on upgrade.

3. Admin Key Management

The admin address used to gate upgrades is itself a critical piece of state. Trace how it is set, updated, and protected:

Critical checks:

• Admin stored as Temporary: if it expires, the contract becomes permanently non-upgradeable AND the upgrade slot is open to whoever sets themselves as admin via any unguarded init path
• Single-step admin transfer: set_admin(new_admin) without two-step handshake means a mistaken address transfer is irreversible
• Admin key not set on init: if the initialize function does not set the admin, the first caller of any admin function can claim admin
• Admin set to the zero address or contract address by accident

Two-step transfer pattern (recommended):

// Step 1: current admin proposes new admin
pub fn propose_admin(env: Env, new_admin: Address) { ... }
// Step 2: new admin accepts
pub fn accept_admin(env: Env) { ... }

4. Upgrade Event Emission

The Soroban host automatically emits a contract_upgraded system event on WASM replacement. However, the contract should also emit its own application-level event for indexer/monitoring visibility:

Finding threshold: Missing contract-level upgrade event is Low/Informational severity — the host event provides a baseline. Flag as Medium if the protocol's stated design includes monitoring hooks that depend on contract events.

5. Immutability Option

Some protocols intend to make contracts permanently immutable after a stabilization period. Check whether such a mechanism exists and is correctly implemented:

Pattern:

pub fn freeze_upgrades(env: Env) {
    admin.require_auth();
    env.storage().instance().set(&DataKey::Frozen, &true);
}

pub fn upgrade(env: Env, new_wasm_hash: BytesN<32>) {
    // Check frozen BEFORE auth (fail fast)
    let frozen = env.storage().instance().get::<_, bool>(&DataKey::Frozen).unwrap_or(false);
    require!(!frozen, "contract is immutable");
    admin.require_auth();
    env.deployer().update_current_contract_wasm(new_wasm_hash);
}

Finding for incorrect ordering: If the frozen check occurs AFTER require_auth, an admin can bypass the intent by upgrading before freezing. The frozen check must be unconditional and first.

Finding Template

**ID**: [CU-N]
**Severity**: [Critical if unguarded upgrade, High if admin management flaw, Medium if migration risk, Low if event/immutability]
**Step Execution**: ✓1,2,3,4,5 | ✗(reasons) | ?(uncertain)
**Rules Applied**: [R6:✓/✗, R10:✓/✗, R12:✓/✗, R13:✓/✗]
**Location**: src/{contract}.rs:LineN
**Title**: {Missing auth / migration gap / admin flaw} in upgrade path — {impact}
**Description**: [Specific upgradeability issue with code reference]
**Impact**: [Unauthorized upgrade / post-upgrade DoS / admin key loss / irrecoverable state]

Step Execution Checklist (MANDATORY)