diff --git a/builtin/logical/pki/acme_jws.go b/builtin/logical/pki/acme_jws.go
index 3ad5e99846..d7207b7fcc 100644
--- a/builtin/logical/pki/acme_jws.go
+++ b/builtin/logical/pki/acme_jws.go
@@ -190,7 +190,10 @@ func verifyEabPayload(acmeState *acmeState, ac *acmeContext, outer *jwsCtx, expe
 	if !ok {
 		return nil, fmt.Errorf("missing required field 'protected': %w", ErrMalformed)
 	}
-	jwkBase64 := rawProtectedBase64.(string)
+	jwkBase64, ok := rawProtectedBase64.(string)
+	if !ok {
+		return nil, fmt.Errorf("failed to parse 'protected' field: %w", ErrMalformed)
+	}
 
 	jwkBytes, err := base64.RawURLEncoding.DecodeString(jwkBase64)
 	if err != nil {
diff --git a/builtin/logical/pki/acme_state_test.go b/builtin/logical/pki/acme_state_test.go
index 6f93503157..e940bc7565 100644
--- a/builtin/logical/pki/acme_state_test.go
+++ b/builtin/logical/pki/acme_state_test.go
@@ -43,6 +43,103 @@ func TestAcmeNonces(t *testing.T) {
 	}
 }
 
+// TestVerifyEabPayloadProtectedFieldValidation verifies that the verifyEabPayload function
+// properly validates and rejects malformed 'protected' fields in ACME External Account Binding
+// (EAB) payloads. It ensures that only string values are accepted and that various non-string
+// types (object, array, number, boolean) produce appropriate error messages.
+func TestVerifyEabPayloadProtectedFieldValidation(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name          string
+		payload       map[string]interface{}
+		expectError   bool
+		expectMessage string
+	}{
+		{
+			name: "valid string protected field",
+			payload: map[string]interface{}{
+				"protected": "eyJhbGciOiAiSFMyNTYifQ",
+			},
+			expectError: false,
+		},
+		{
+			name: "missing protected field",
+			payload: map[string]interface{}{
+				"payload":   "test",
+				"signature": "test",
+			},
+			expectError:   true,
+			expectMessage: "missing required field 'protected'",
+		},
+		{
+			name: "protected field as object",
+			payload: map[string]interface{}{
+				"protected": map[string]interface{}{ // should be a string, not an object
+					"alg": "HS256",
+				},
+				"payload":   "test",
+				"signature": "test",
+			},
+			expectError:   true,
+			expectMessage: "failed to parse 'protected' field",
+		},
+		{
+			name: "protected field as array",
+			payload: map[string]interface{}{
+				"protected": []interface{}{"test"}, // should be a string, not an array
+				"payload":   "test",
+				"signature": "test",
+			},
+			expectError:   true,
+			expectMessage: "failed to parse 'protected' field",
+		},
+		{
+			name: "protected field as number",
+			payload: map[string]interface{}{
+				"protected": 12345, // should be a string, not a number
+				"payload":   "test",
+				"signature": "test",
+			},
+			expectError:   true,
+			expectMessage: "failed to parse 'protected' field",
+		},
+		{
+			name: "protected field as boolean",
+			payload: map[string]interface{}{
+				"protected": true, // should be a string, not a boolean
+				"payload":   "test",
+				"signature": "test",
+			},
+			expectError:   true,
+			expectMessage: "failed to parse 'protected' field",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			acmeState := NewACMEState()
+			acmeCtx := &acmeContext{}
+			outerJws := &jwsCtx{}
+
+			_, err := verifyEabPayload(acmeState, acmeCtx, outerJws, "/new-account", tc.payload)
+
+			if tc.expectError {
+				require.Error(t, err, "expected error but got none")
+				require.Contains(t, err.Error(), tc.expectMessage, "error message does not match")
+				require.NotEmpty(t, err.Error())
+			} else {
+				// For valid protected field, we expect an error later in the flow
+				// (since we don't have real base64 data), but it should NOT be from parsing the protected field
+				if err != nil {
+					require.NotContains(t, err.Error(), "failed to parse 'protected' field",
+						"should not fail at protected field parsing stage")
+				}
+			}
+		})
+	}
+}
+
 // TestErrorResponseNoSubproblems builds the http body that exists in the header of an ACME error response and checks
 // in a simple case that "type" and "detail" two fields on the body do exist, but that "subproblems" a field which is
 // optional, is omitted because it does not exist in this case (rather than being included with a value null which can
diff --git a/changelog/_12260.txt b/changelog/_12260.txt
new file mode 100644
index 0000000000..b0173b670c
--- /dev/null
+++ b/changelog/_12260.txt
@@ -0,0 +1,3 @@
+```release-note:bug
+secrets/pki: fix panic during acme account creation with malformed protected field.
+``