diff --git a/packages/testing/src/consensus_testing/test_fixtures/verify_signatures.py b/packages/testing/src/consensus_testing/test_fixtures/verify_signatures.py
index 29ebe35f9..f7a91839f 100644
--- a/packages/testing/src/consensus_testing/test_fixtures/verify_signatures.py
+++ b/packages/testing/src/consensus_testing/test_fixtures/verify_signatures.py
@@ -62,6 +62,10 @@ class VerifySignaturesTest(BaseConsensusFixture):
       the block's proposer_index field. Use this to exercise the
       validator-bounds check that the builder skips because its round-
       robin selection stays within range by construction.
+    - ``{"operation": "clear_first_attestation_bits"}``: Replace the
+      first body attestation with one whose aggregation_bits carry no
+      set bit. Exercises the empty-participants check inside
+      signature verification.
 
     Tampered blocks bypass the builder's structural invariants. The
     resulting fixture pins the exact rejection a client must raise when
@@ -164,4 +168,24 @@ def _apply_tamper(self, signed_block: SignedBlock) -> SignedBlock:
             )
             return signed_block.model_copy(update={"block": tampered_block})
 
+        if operation == "clear_first_attestation_bits":
+            from lean_spec.subspecs.containers.attestation import AggregatedAttestation
+            from lean_spec.subspecs.containers.attestation.aggregation_bits import (
+                AggregationBits,
+            )
+            from lean_spec.subspecs.containers.block.types import AggregatedAttestations
+            from lean_spec.types import Boolean
+
+            body = signed_block.block.body
+            original = body.attestations.data
+            if not original:
+                raise ValueError("clear_first_attestation_bits requires at least one attestation")
+            first = original[0]
+            empty_bits = AggregationBits(data=[Boolean(False)] * len(first.aggregation_bits.data))
+            cleared = AggregatedAttestation(aggregation_bits=empty_bits, data=first.data)
+            new_attestations = AggregatedAttestations(data=[cleared, *original[1:]])
+            new_body = body.model_copy(update={"attestations": new_attestations})
+            new_block = signed_block.block.model_copy(update={"body": new_body})
+            return signed_block.model_copy(update={"block": new_block})
+
         raise ValueError(f"Unknown tamper operation: {operation!r}")
diff --git a/tests/consensus/devnet/verify_signatures/test_empty_aggregation_bits.py b/tests/consensus/devnet/verify_signatures/test_empty_aggregation_bits.py
new file mode 100644
index 000000000..293570826
--- /dev/null
+++ b/tests/consensus/devnet/verify_signatures/test_empty_aggregation_bits.py
@@ -0,0 +1,58 @@
+"""Signature verification: empty aggregation_bits rejection vector."""
+
+import pytest
+from consensus_testing import (
+    AggregatedAttestationSpec,
+    BlockSpec,
+    VerifySignaturesTestFiller,
+    generate_pre_state,
+)
+
+from lean_spec.subspecs.containers.slot import Slot
+from lean_spec.subspecs.containers.validator import ValidatorIndex
+
+pytestmark = pytest.mark.valid_until("Devnet")
+
+
+def test_empty_aggregation_bits_rejected(
+    verify_signatures_test: VerifySignaturesTestFiller,
+) -> None:
+    """A signed block whose attestation references zero participants is rejected.
+
+    Scenario
+    --------
+    - Anchor state has 3 validators.
+    - Block at slot 1 carries one aggregated attestation.
+    - The tamper hook replaces the first attestation's aggregation_bits
+      with a bitfield where no bit is set.
+
+    Expected Behavior
+    -----------------
+    Signature verification fails with AssertionError:
+    "Aggregated attestation must reference at least one validator"
+
+    Why This Matters
+    ----------------
+    An aggregated attestation with no participants carries no signed
+    message. The block builder never produces one because its
+    aggregation pass starts from a non-empty validator set, but a
+    malicious peer could. Clients must raise before attempting to look
+    up public keys for a zero-participant attestation.
+    """
+    verify_signatures_test(
+        anchor_state=generate_pre_state(num_validators=3),
+        block=BlockSpec(
+            slot=Slot(1),
+            attestations=[
+                AggregatedAttestationSpec(
+                    validator_ids=[ValidatorIndex(0)],
+                    slot=Slot(1),
+                    target_slot=Slot(0),
+                    target_root_label="genesis",
+                    valid_signature=False,
+                ),
+            ],
+        ),
+        tamper={"operation": "clear_first_attestation_bits"},
+        expect_exception=AssertionError,
+    )