> ## Documentation Index > Fetch the complete documentation index at: https://docs.tac.build/llms.txt > Use this file to discover all available pages before exploring further. # TVM (TON) Smart Contacts # Bug Bounty Report Guide The report template below covers vulnerabilities in TAC-related FunC / Tact contracts deployed on TON. Tools: Blueprint, toncli, tonutils-go, @ton/ton (JS SDK). ## Report Template ``` SECURITY VULNERABILITY REPORT — in Date: YYYY-MM-DD Status: =============================== EXECUTIVE SUMMARY =============================== =============================== VULNERABILITY DETAILS =============================== Contract: , , line Deployed: EQ
Class: Root cause: Vulnerable snippet: Fixed version: TON-specific notes: Prerequisites: =============================== EXPLOITATION STEPS =============================== Message body: op: payload: 1. 2. ... Blueprint test / script: =============================== POC RESULTS =============================== Contract: EQ
Exploit TX: Balance table:
before → after delta Scaling: =============================== IMPACT ASSESSMENT =============================== Severity: 1. 2. =============================== RECOMMENDED FIX =============================== Immediate: Long-term: Audit: =============================== PROOF-OF-CONCEPT CODE =============================== =============================== DISCLOSURE TIMELINE =============================== YYYY-MM-DD YYYY-MM-DD ``` ## Report Template Commentary ### 1. Title and Metadata ``` SECURITY VULNERABILITY REPORT — in Date: YYYY-MM-DD Status: ``` Useful classes: `Unprotected Internal Message`, `Bounce Exploit`, `Storage Drain`, `Replay Attack (no op-guard)`, `Incorrect Fees / Forward Gas`, `Cell Overflow`, `Tact Inheritance Access Control`. ### 2. Executive Summary Same four questions: 1. **What is broken?** — which op-code handler / recv\_internal branch. 2. **What does the attacker gain?** — TON drained / token minted / ownership. 3. **How much?** — contract balance or jetton supply at risk. 4. **Is it repeatable?** — per-message / once / needs timing. **Example:** ``` The jetton minter's recv_internal handler does not verify the sender against the admin address before processing op::mint. Any wallet can send a mint message and create arbitrary tokens, inflating the supply without limit. Contract balance at risk: 0 TON (no drain) Token supply at risk: unlimited inflation Attack cost: ~0.05 TON (gas) ``` ### 3. Vulnerability Details #### 3.1 Affected Contract ``` Contract: contracts/JettonMinter.fc (or .tact) Handler: recv_internal — op::mint branch (line ~47) Deployed: EQ
(mainnet / testnet) ``` Provide a Tonviewer / Tonscan link if the contract is verified. #### 3.2 Root Cause > The `op::mint` branch reads `sender_address` from the message slice but > never calls `throw_unless(73, equal_slices(sender_address, storage::admin))` > before executing the mint logic. #### 3.3 Vulnerable Code Snippet ```func theme={null} ;; JettonMinter.fc ~line 47 — VULNERABLE if (op == op::mint) { ;; ← missing: throw_unless(73, equal_slices(sender, admin)); slice to_address = in_msg_body~load_msg_addr(); int amount = in_msg_body~load_coins(); mint_tokens(to_address, amount); ... } ``` #### 3.4 Fixed Version ```func theme={null} if (op == op::mint) { throw_unless(73, equal_slices(sender, admin)); ;; ← added slice to_address = in_msg_body~load_msg_addr(); int amount = in_msg_body~load_coins(); mint_tokens(to_address, amount); ... } ``` #### 3.5 TON-specific Considerations * **Bounce messages:** does the contract handle `op::excesses` / bounced messages safely? A missing bounce handler can leave funds locked. * **Forward gas:** does the contract forward enough gas for sub-messages? Under-forwarding silently fails without reverting the parent tx. * **Storage fees:** contracts with no incoming messages will be frozen and then deleted. Does the attacker benefit from this? * **Replay:** TON has no global nonce — contracts must implement their own seqno or use the `valid_until` trick. ### 4. Exploitation Steps For each step, include the message body layout (op + payload): ``` 1. Build a mint message: op: 0x642b7d07 (op::mint) to_address: attacker_wallet amount: 1_000_000_000_000 (1 000 000 jettons, 6 decimals) 2. Send from any wallet with 0.1 TON attached (covers gas + forward). 3. Check attacker's jetton wallet balance — should increase by 1 000 000. 4. Repeat for unlimited supply inflation. ``` Blueprint test skeleton: ```typescript theme={null} it("mints without admin auth", async () => { const attacker = await blockchain.treasury("attacker"); await minter.sendMint(attacker.getSender(), { toAddress: attacker.address, amount: toNano("1000000"), value: toNano("0.1"), }); const balance = await getJettonBalance(attacker.address); expect(balance).toEqual(toNano("1000000")); // should FAIL if patched }); ``` ### 5. PoC Results Required: * Contract address (`EQ...`). * Transaction hash (lt + hash, or Tonviewer link). * Message trace (Tonviewer shows the full message tree). * Jetton balance / TON balance before and after. **Example:** ``` CONTRACT BALANCE BEFORE BALANCE AFTER DELTA -------- -------------- ------------- ----- JettonMinter 100 000 supply 1 100 000 +1 000 000 minted Attacker jetton wlt 0 1 000 000 +1 000 000 Exploit TX: https://tonviewer.com/transaction/ Gas spent: 0.048 TON ``` #### 5.1 Scaling Economics ``` Calls Amount per call Total minted Gas cost ----- --------------- ------------ -------- 1 1 000 000 1 000 000 0.05 TON 100 1 000 000 100 000 000 5.0 TON ``` ### 6. Impact Assessment ``` Severity: CRITICAL 1. Unlimited token inflation — total supply can be minted to any address. 2. No admin role required — any wallet can exploit. 3. Per-message — repeatable indefinitely. 4. DEX liquidity pools backed by this jetton become worthless. ``` TON-specific severity boosters: * contract holds significant TON balance (storage drain possible), * contract is a bridge or DEX vault, * no upgrade / pause mechanism exists. ### 7. Recommended Fix #### Immediate ``` Add sender verification as the first statement in the op::mint branch: throw_unless(73, equal_slices(sender, storage::admin)); ``` #### Long-term ``` Use Tact's @internal access modifier or a dedicated access-control library. Add Blueprint unit tests that assert every privileged op reverts for non-admin. ``` #### Adjacent Audit ``` Review all other privileged ops in recv_internal: op::change_admin, op::burn_notification, op::set_content. Verify bounce handler is implemented for all outgoing messages carrying value. ``` ### 8. Proof-of-Concept Code Provide a **Blueprint** test or a minimal **@ton/ton** script: ```typescript theme={null} // test/JettonMinterExploit.spec.ts import { Blockchain, SandboxContract } from "@ton/sandbox"; import { JettonMinter } from "../wrappers/JettonMinter"; import { toNano } from "@ton/ton"; describe("Exploit: unrestricted mint", () => { let blockchain: Blockchain; let minter: SandboxContract; beforeEach(async () => { blockchain = await Blockchain.create(); // deploy with 1 TON initial balance minter = ...; // standard deploy }); it("mints 1M tokens without admin", async () => { const attacker = await blockchain.treasury("attacker"); const result = await minter.sendMint(attacker.getSender(), { toAddress: attacker.address, amount: toNano("1000000"), value: toNano("0.1"), }); expect(result.transactions).toHaveTransaction({ success: true }); // if this passes — the bug is confirmed }); }); ```