fix(axon): reject requests with missing signature in default_verify

bittensor/core/axon.py

@@ -974,9 +974,10 @@ async def default_verify(self, synapse: "Synapse"):
                 ):
                     raise Exception("Nonce is too old, a newer one was last processed")
 
-            if synapse.dendrite.signature and not keypair.verify(
-                message, synapse.dendrite.signature
-            ):
+            if not synapse.dendrite.signature:
+                raise Exception("Missing Signature")
+
+            if not keypair.verify(message, synapse.dendrite.signature):
                 raise Exception(
                     f"Signature mismatch with {message} and {synapse.dendrite.signature}"
                 )

tests/unit_tests/test_axon.py

@@ -21,14 +21,15 @@
 from bittensor.core.errors import RunException
 from bittensor.core.settings import version_as_int
 from bittensor.core.stream import StreamingSynapse
-from bittensor.core.synapse import Synapse
+from bittensor.core.synapse import Synapse, TerminalInfo
 from bittensor.core.threadpool import PriorityThreadPoolExecutor
 from bittensor.utils.axon_utils import (
     allowed_nonce_window_ns,
     calculate_diff_seconds,
     ALLOWED_DELTA,
     NANOSECONDS_IN_SECOND,
 )
+from bittensor_wallet import Keypair
 
 
 def test_attach_initial(mock_get_external_ip):
@@ -755,6 +756,76 @@ def test_nonce_diff_seconds(nonce_offset_seconds):
     )
 
 
+# ---------------------------------------------------------------------------
+# default_verify signature checks
+# ---------------------------------------------------------------------------
+def _make_default_verify_inputs():
+    """Build an (axon, synapse, dendrite_keypair) trio for default_verify.
+
+    The synapse carries a fresh nonce (so the v7.2 freshness check passes) and
+    a valid dendrite hotkey; each test sets `synapse.dendrite.signature` to
+    probe the signature branch.
+    """
+    dendrite_keypair = Keypair.create_from_uri("//Alice")
+    receiver_keypair = Keypair.create_from_uri("//Bob")
+    axon = Axon(
+        ip="192.0.2.1",
+        external_ip="192.0.2.1",
+        wallet=MockWallet(MockHotkey(receiver_keypair.ss58_address)),
+    )
+    synapse = SynapseMock()
+    synapse.dendrite = TerminalInfo(
+        hotkey=dendrite_keypair.ss58_address,
+        nonce=time.time_ns(),
+        uuid="5ecbd69c-1cec-11ee-b0dc-e29ce36fec1a",
+        version=version_as_int,
+    )
+    return axon, synapse, dendrite_keypair
+
+
+def _default_verify_message(axon, synapse):
+    return (
+        f"{synapse.dendrite.nonce}.{synapse.dendrite.hotkey}."
+        f"{axon.wallet.hotkey.ss58_address}.{synapse.dendrite.uuid}."
+        f"{synapse.computed_body_hash}"
+    )
+
+
+@pytest.mark.asyncio
+async def test_default_verify_valid_signature_passes():
+    axon, synapse, dendrite_keypair = _make_default_verify_inputs()
+    message = _default_verify_message(axon, synapse)
+    synapse.dendrite.signature = "0x" + dendrite_keypair.sign(message).hex()
+
+    await axon.default_verify(synapse)
+
+    endpoint_key = f"{synapse.dendrite.hotkey}:{synapse.dendrite.uuid}"
+    assert axon.nonces[endpoint_key] == synapse.dendrite.nonce
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("empty_sig", ["", None])
+async def test_default_verify_missing_signature_raises(empty_sig):
+    # Regression: a falsy signature must NOT skip verification. Previously the
+    # check was `if signature and not verify(...)`, so an empty/None signature
+    # short-circuited and the request was accepted, allowing hotkey spoofing.
+    axon, synapse, _ = _make_default_verify_inputs()
+    synapse.dendrite.signature = empty_sig
+
+    with pytest.raises(Exception, match="Missing Signature"):
+        await axon.default_verify(synapse)
+
+
+@pytest.mark.asyncio
+async def test_default_verify_wrong_signature_raises():
+    # A present-but-invalid signature is still rejected (unchanged behavior).
+    axon, synapse, _ = _make_default_verify_inputs()
+    synapse.dendrite.signature = "0x" + ("00" * 64)
+
+    with pytest.raises(Exception, match="Signature mismatch"):
+        await axon.default_verify(synapse)
+
+
 # Mimicking axon default_verify nonce verification
 # True: Nonce is fresh, False: Nonce is old
 def is_nonce_within_allowed_window(synapse_nonce, allowed_window_ns):