fix: filter a fake ETH token from the balance list too (closes #235)

KNOWN_SYMBOLS maps "ETH" to null, and the three surfaces that show tokens
disagreed about what that means. The transaction history and the Send
token selector read it as "no contract may bear this symbol" and filtered
a fake ETH ERC-20; the balance list's guard required a non-null mapping,
so the same token was listed as a holding named ETH next to the user's
real ETH. That is the surface where the user forms their belief about
what they own.

The rule now lives in src/shared/symbolSpoof.js and all three sites call
it, so a fourth reading is not available to a future call site. A symbol
mapped to null belongs to the native asset and may be borne by no
contract at all; the native exemption is "has no contract address", not
"the symbol is ETH", so a second null-mapped entry needs no call-site
change.

The user's real ETH balance is untouched: it is read over RPC in
refreshBalances and never enters fetchTokenBalances, whose loop only
considers explorer rows of type ERC-20.

tests/symbolSpoof.test.js drives the same fake ETH token through all
three surfaces plus refreshBalances, which reports the native balance
unchanged while the fake token is gone. Its two balance-list cases were
watched failing against the unmodified call sites first.

tests/symbolSpoof.test.js

@@ -0,0 +1,296 @@
+// Tests for the known-symbol spoof rule (src/shared/symbolSpoof.js) and for
+// its application on all three surfaces that show tokens: the transaction
+// history, the Send token selector, and the balance list.
+//
+// Issue #235: the three surfaces disagreed about what a `null` entry in
+// KNOWN_SYMBOLS means.  The history and the selector read it as "no contract
+// may bear this symbol" and filtered a fake `ETH` ERC-20; the balance list
+// read it as "no comparison is possible" and listed the fake token next to
+// the user's real ETH, which is where a user forms their belief about what
+// they own.  The rule now lives in one module, so a fourth surface cannot
+// reintroduce a fourth reading, and these tests assert the same attack on
+// each surface.
+//
+// Nothing here touches the network: global.fetch is a throwing stub and the
+// only fetch path in the modules under test (debugFetch, from
+// src/shared/log) is mocked at the module boundary.
+
+// The RPC provider is replaced so that refreshBalances can be driven end to
+// end: the native balance it reports must survive a balance list in which
+// every ERC-20 row is a fake ETH.  Everything else in ethers is the real
+// module, including the formatters the assertions depend on.
+jest.mock("ethers", () => {
+    const actual = jest.requireActual("ethers");
+    class StubProvider {
+        async getBalance() {
+            return 1234500000000000000n;
+        }
+        async lookupAddress() {
+            return null;
+        }
+    }
+    return {
+        ...actual,
+        JsonRpcProvider: StubProvider,
+        Network: { from: () => ({}) },
+    };
+});
+
+jest.mock("../src/shared/log", () => ({
+    log: {
+        debugf: () => {},
+        infof: () => {},
+        warnf: () => {},
+        errorf: () => {},
+    },
+    debugFetch: jest.fn(),
+    setRuntimeDebug: () => {},
+    isDebug: () => false,
+}));
+
+global.fetch = jest.fn(() => {
+    throw new Error("tests must not perform network requests");
+});
+global.chrome = {
+    storage: { local: { get: async () => ({}), set: async () => {} } },
+};
+
+const { isSpoofedSymbol } = require("../src/shared/symbolSpoof");
+const { KNOWN_SYMBOLS } = require("../src/shared/tokenList");
+const { filterTransactions } = require("../src/shared/transactions");
+const {
+    fetchTokenBalances,
+    refreshBalances,
+} = require("../src/shared/balances");
+const { renderSendTokenSelect } = require("../src/popup/views/send");
+const { state } = require("../src/shared/state");
+const { debugFetch } = require("../src/shared/log");
+
+// The fake "Ethereum" token with symbol "ETH" from the attack documented in
+// README.md, given a holder count high enough to clear every other filter so
+// that only the known-symbol rule can catch it.
+const FAKE_ETH_CONTRACT = "0xd05339f9ea5ab9d9f03b9d57f671d2abd1f55c82";
+const HOLDER = "0x66133e8ea0f5d1d612d2502a968757d1048c214a";
+const USDC_CONTRACT = "0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48";
+const WETH_CONTRACT = "0xc02aaa39b223fe8d0a0e5c4f27ead9083c756cc2";
+const BLOCKSCOUT = "https://eth.blockscout.com/api/v2";
+
+describe("the shared rule", () => {
+    test('"ETH" is still the null-mapped symbol these tests assume', () => {
+        expect(KNOWN_SYMBOLS.get("ETH")).toBeNull();
+    });
+
+    test("a contract bearing a null-mapped symbol is a spoof", () => {
+        expect(isSpoofedSymbol("ETH", FAKE_ETH_CONTRACT)).toBe(true);
+    });
+
+    test("even a genuine contract may not bear a null-mapped symbol", () => {
+        expect(isSpoofedSymbol("ETH", WETH_CONTRACT)).toBe(true);
+    });
+
+    test("the native asset carries no contract and is never a spoof", () => {
+        expect(isSpoofedSymbol("ETH", null)).toBe(false);
+        expect(isSpoofedSymbol("ETH", undefined)).toBe(false);
+        expect(isSpoofedSymbol("ETH", "")).toBe(false);
+    });
+
+    // The native exemption is "has no contract address", not "the symbol is
+    // ETH".  A second null-mapped symbol added to the table later inherits
+    // both halves of the rule without any call site being revisited.
+    test("a newly null-mapped symbol behaves the same way", () => {
+        const added = !KNOWN_SYMBOLS.has("XTZTEST");
+        KNOWN_SYMBOLS.set("XTZTEST", null);
+        try {
+            expect(isSpoofedSymbol("XTZTEST", FAKE_ETH_CONTRACT)).toBe(true);
+            expect(isSpoofedSymbol("XTZTEST", null)).toBe(false);
+        } finally {
+            if (added) KNOWN_SYMBOLS.delete("XTZTEST");
+        }
+    });
+
+    test("a known symbol from its own contract is not a spoof", () => {
+        expect(isSpoofedSymbol("USDC", USDC_CONTRACT)).toBe(false);
+        expect(isSpoofedSymbol("usdc", USDC_CONTRACT.toUpperCase())).toBe(
+            false,
+        );
+    });
+
+    test("a known symbol from another contract is a spoof", () => {
+        expect(isSpoofedSymbol("USDC", FAKE_ETH_CONTRACT)).toBe(true);
+    });
+
+    test("a symbol that is not in the table is not judged here", () => {
+        expect(isSpoofedSymbol("SPAMTKN", FAKE_ETH_CONTRACT)).toBe(false);
+    });
+});
+
+describe("surface 1: the transaction history", () => {
+    function fakeEthTransfer() {
+        return {
+            hash: "0x" + "1".repeat(64),
+            symbol: "ETH",
+            contractAddress: FAKE_ETH_CONTRACT,
+            holders: 900000,
+            valueGwei: null,
+            isContractCall: false,
+        };
+    }
+
+    test("a fake ETH token transfer is filtered", () => {
+        const result = filterTransactions([fakeEthTransfer()], {
+            hideSpoofedSymbols: true,
+            hideFraudContracts: true,
+            hideLowHolderTokens: true,
+            hideDustTransactions: true,
+            dustThresholdGwei: 100000,
+        });
+        expect(result.transactions).toEqual([]);
+    });
+
+    test("a real native ETH transfer survives", () => {
+        const native = {
+            hash: "0x" + "2".repeat(64),
+            symbol: "ETH",
+            contractAddress: null,
+            holders: null,
+            valueGwei: 5000000,
+            isContractCall: false,
+        };
+        const result = filterTransactions([native], {
+            hideSpoofedSymbols: true,
+            hideFraudContracts: true,
+            hideLowHolderTokens: true,
+            hideDustTransactions: true,
+            dustThresholdGwei: 100000,
+        });
+        expect(result.transactions).toEqual([native]);
+    });
+});
+
+describe("surface 2: the Send token selector", () => {
+    let select;
+
+    function render(tokenBalances) {
+        select = { innerHTML: "", children: [] };
+        select.appendChild = (child) => select.children.push(child);
+        globalThis.document = {
+            getElementById: (id) => (id === "send-token" ? select : null),
+            createElement: () => ({ value: "", textContent: "" }),
+        };
+        renderSendTokenSelect({
+            address: "0x" + "a".repeat(40),
+            tokenBalances,
+        });
+    }
+
+    beforeEach(() => {
+        state.fraudContracts = [];
+        state.hideLowHolderTokens = true;
+    });
+
+    test("a fake ETH token is not selectable", () => {
+        render([
+            {
+                address: FAKE_ETH_CONTRACT,
+                symbol: "ETH",
+                decimals: 18,
+                balance: "0.005",
+                holders: 900000,
+            },
+        ]);
+        expect(select.children).toEqual([]);
+    });
+
+    test("native ETH remains the always-present option", () => {
+        render([]);
+        expect(select.innerHTML).toBe('<option value="ETH">ETH</option>');
+    });
+});
+
+describe("surface 3: the balance list", () => {
+    function respondWith(items) {
+        debugFetch.mockImplementation(async () => ({
+            ok: true,
+            status: 200,
+            statusText: "OK",
+            json: async () => items,
+        }));
+    }
+
+    function fakeEthItem(overrides = {}) {
+        return {
+            value: "5000000000000000",
+            token: {
+                type: "ERC-20",
+                address_hash: FAKE_ETH_CONTRACT,
+                symbol: "ETH",
+                name: "Ethereum",
+                decimals: "18",
+                holders_count: "900000",
+                ...overrides,
+            },
+        };
+    }
+
+    beforeEach(() => {
+        debugFetch.mockReset();
+    });
+
+    // The bug in issue #235: this token cleared the balance list's own
+    // 1,000-holder floor and was listed as a holding named ETH.
+    test("a fake ETH token clearing the holder floor is filtered", async () => {
+        respondWith([fakeEthItem()]);
+        expect(await fetchTokenBalances(HOLDER, BLOCKSCOUT, [])).toEqual([]);
+    });
+
+    test("tracking the fake token manually does not admit it either", async () => {
+        respondWith([fakeEthItem({ holders_count: "0" })]);
+        const balances = await fetchTokenBalances(HOLDER, BLOCKSCOUT, [
+            { address: FAKE_ETH_CONTRACT },
+        ]);
+        expect(balances).toEqual([]);
+    });
+
+    test("a genuine token keeps its place in the list", async () => {
+        respondWith([
+            fakeEthItem({
+                address_hash: USDC_CONTRACT,
+                symbol: "USDC",
+                name: "USD Coin",
+                decimals: "6",
+            }),
+        ]);
+        const balances = await fetchTokenBalances(HOLDER, BLOCKSCOUT, []);
+        expect(balances).toHaveLength(1);
+        expect(balances[0].symbol).toBe("USDC");
+    });
+
+    // The trap in this change: the user's real ETH balance is not an ERC-20
+    // and is fetched over RPC in refreshBalances, so it never passes through
+    // this loop at all.  An explorer row that is not an ERC-20 is dropped
+    // before the symbol rule is consulted.
+    test("a non-ERC-20 row claiming ETH never reaches the symbol rule", async () => {
+        respondWith([fakeEthItem({ type: "ERC-721" })]);
+        expect(await fetchTokenBalances(HOLDER, BLOCKSCOUT, [])).toEqual([]);
+    });
+
+    // The money test: the user holds real ETH and has been airdropped a fake
+    // ETH ERC-20.  The fake is gone from the list of tokens; the real balance
+    // is exactly what the node reported.
+    test("the real native ETH balance survives a fake ETH airdrop", async () => {
+        respondWith([fakeEthItem()]);
+        const addr = { address: HOLDER };
+        await refreshBalances(
+            [{ addresses: [addr] }],
+            "https://rpc.example.invalid",
+            BLOCKSCOUT,
+            [],
+        );
+        expect(addr.balance).toBe("1.2345");
+        expect(addr.tokenBalances).toEqual([]);
+    });
+
+    test("no test in this file performed a network request", () => {
+        expect(global.fetch).not.toHaveBeenCalled();
+    });
+});