diff --git a/src/CertManager.sol b/src/CertManager.sol
index 79852a0..ef6be5a 100644
--- a/src/CertManager.sol
+++ b/src/CertManager.sol
@@ -589,8 +589,15 @@ contract CertManager is ICertManager {
     function _certSignature(bytes memory certificate, Asn1Ptr sigPtr) internal pure returns (bytes memory sigPacked) {
         Asn1Ptr sigBPtr = certificate.bitstring(sigPtr);
         Asn1Ptr sigRoot = certificate.rootOf(sigBPtr);
+        _requireAsn1Tag(certificate, sigRoot, 0x30);
         Asn1Ptr sigRPtr = certificate.firstChildOf(sigRoot);
         Asn1Ptr sigSPtr = certificate.nextSiblingOf(sigRPtr);
+        if (
+            sigRoot.header() + sigRoot.totalLength() != sigBPtr.content() + sigBPtr.length()
+                || sigSPtr.header() + sigSPtr.totalLength() != sigRoot.content() + sigRoot.length()
+        ) {
+            revert InvalidAsn1Tag();
+        }
         (uint128 rhi, uint256 rlo) = certificate.uint384At(sigRPtr);
         (uint128 shi, uint256 slo) = certificate.uint384At(sigSPtr);
         sigPacked = abi.encodePacked(rhi, rlo, shi, slo);
diff --git a/test/CertManager.t.sol b/test/CertManager.t.sol
index 5c1bd3e..eedc5c3 100644
--- a/test/CertManager.t.sol
+++ b/test/CertManager.t.sol
@@ -263,6 +263,38 @@ contract CertManagerTest is Test {
         cm.verifyCACertWithHints(rootTwin, rootHash, hints);
     }
 
+    function test_VerifyCACertWithHints_RejectsSignatureWrapperTagSubstitution() public {
+        vm.warp(1775145600);
+        CertManager cm = new CertManager(new P384Verifier());
+        P384HintCollector collector = new P384HintCollector();
+
+        bytes32 rootHash = keccak256(CB0);
+        bytes memory parentPubKey = cm.loadVerified(rootHash).pubKey;
+        bytes memory hints = collector.collectCertSignatureHints(CB1, parentPubKey);
+
+        bytes memory mutated = bytes.concat(CB1);
+        (,, Asn1Ptr sigRoot,) = _certSignaturePtrs(mutated);
+        mutated[sigRoot.header()] = 0x31; // constructed SET with the same r/s children.
+
+        vm.expectRevert(CertManager.InvalidAsn1Tag.selector);
+        cm.verifyCACertWithHints(mutated, rootHash, hints);
+    }
+
+    function test_VerifyCACertWithHints_RejectsTrailingSignatureFields() public {
+        vm.warp(1775145600);
+        CertManager cm = new CertManager(new P384Verifier());
+        P384HintCollector collector = new P384HintCollector();
+
+        bytes32 rootHash = keccak256(CB0);
+        bytes memory parentPubKey = cm.loadVerified(rootHash).pubKey;
+        bytes memory hints = collector.collectCertSignatureHints(CB1, parentPubKey);
+
+        bytes memory mutated = _appendSignatureTrailingField(CB1);
+
+        vm.expectRevert(CertManager.InvalidAsn1Tag.selector);
+        cm.verifyCACertWithHints(mutated, rootHash, hints);
+    }
+
     function test_VerifyCACertWithHints_RejectsOuterTagSubstitution() public {
         vm.warp(1775145600);
         CertManager cm = new CertManager(new P384Verifier());
@@ -338,6 +370,34 @@ contract CertManagerTest is Test {
         _writeDerLength(result, sigRoot, _addDelta(sigRoot.length(), delta));
     }
 
+    function _appendSignatureTrailingField(bytes memory certificate) internal pure returns (bytes memory result) {
+        (Asn1Ptr root, Asn1Ptr sigPtr, Asn1Ptr sigRoot,) = _certSignaturePtrs(certificate);
+        bytes memory extraInteger = hex"020100";
+        int256 delta = int256(extraInteger.length);
+        result = _insertBytes(certificate, sigRoot.content() + sigRoot.length(), extraInteger);
+
+        _writeDerLength(result, root, _addDelta(root.length(), delta));
+        _writeDerLength(result, sigPtr, _addDelta(sigPtr.length(), delta));
+        _writeDerLength(result, sigRoot, _addDelta(sigRoot.length(), delta));
+    }
+
+    function _insertBytes(bytes memory input, uint256 offset, bytes memory inserted)
+        internal
+        pure
+        returns (bytes memory result)
+    {
+        result = new bytes(input.length + inserted.length);
+        for (uint256 i = 0; i < offset; ++i) {
+            result[i] = input[i];
+        }
+        for (uint256 i = 0; i < inserted.length; ++i) {
+            result[offset + i] = inserted[i];
+        }
+        for (uint256 i = offset; i < input.length; ++i) {
+            result[i + inserted.length] = input[i];
+        }
+    }
+
     function _certSignaturePtrs(bytes memory certificate)
         internal
         pure