When a serial to Ethernet converter (also called a serial device server) is being evaluated for purchase, the usual comparison points are RS232/RS485 port types and counts, baud rate, TCP/UDP working modes, and finally price. Security features rarely make it onto the comparison list. The device sits between serial equipment — PLCs, meters, controllers — and the IP network, which effectively opens one more network-facing entrance on the production data path. Security researchers have publicly disclosed serious vulnerabilities found in serial to ethernet converters, and leaving security out of the purchasing decision usually costs far more after deployment than it does at the specification stage.
Spec sheets document port counts and baud rate in dedicated rows, but security capabilities are rarely listed with the same clarity. Most of them have to be verified from the datasheet notes, the user manual, or the vendor's security documentation — which is exactly why they need to be on the buyer's own checklist.
One group of specifications answers "will the device keep running": metal housing, wide-temperature operation, watchdog, power protection. These ensure the unit survives the site and recovers by itself if it hangs. That is hardware reliability.
A second group answers "will the data stay protected": encrypted links, authentication, credential and port management, firmware updates. Publicly disclosed vulnerabilities are mostly found in this second group. When a device sits on the network with unencrypted links, default credentials, and no firmware update path, the entire serial link is effectively handed to anyone who can reach that network.
Spec sheets are usually quite complete about the first group. The second group has to be checked item by item, because the rows for it are often missing or buried in the fine print. Both groups matter; the second one is the one usually overlooked.
1. Is encryption stated in plain sight?The spec sheet should be checked for SSL/TLS, and the vendor should be asked which operating modes it covers. Encrypting only the web configuration page is not enough; the data path between the serial device and the server needs protection too. Both the USR-TCP232-410s and the USR-N520 state SSL/TLS encryption covering TCP Client, HTTP Client and MQTT modes, together with two-way certificate authentication. Two-way authentication means each side of the connection verifies the other's identity, so a rogue endpoint cannot simply impersonate the server or the device. This kind of detail should be found directly in the specifications, not delivered later as an explanation from the sales team.
2. How large is the exposure by default?Default account credentials need to be changeable, and unused services and protocols need to be disabled. Before a unit is connected to a production line, basic hardening should be done: change the default password, close the ports that are not used, and disable plaintext protocols wherever they are not required. If the device does not allow any of these changes, the exposure stays open for the entire service life.
3. Is there a path after a disclosure?Firmware should be field-upgradable, and the vendor should keep issuing releases. For a device with no firmware update path, the only remedy after its model is named in a public disclosure is full replacement. With upgradeable firmware, a single release can cover every installed site running that model. It is also worth checking whether the vendor publishes firmware release notes and security advisories; that shows the update channel is maintained rather than theoretical.
4. Can the device recover from abnormal states?Consider whether configuration can be restored to factory defaults, whether a watchdog resets the unit after a hang, and whether parameters survive a power cycle. For unattended field equipment, this determines whether a fault costs a site visit or can be resolved remotely.
A disclosure of serious vulnerabilities in serial to ethernet converters has appeared in the technical community. For buyers, the meaningful part is not the vulnerability details but the timing of the remedy. These converters run unattended next to production networks; once one is remotely controlled, the serial equipment behind it is exposed as well. For sites already deployed, the available remedies are usually limited to firmware upgrades or wholesale replacement, and neither is free. By the time a vulnerability is public, the affected models are already known, and the fleet owner is left choosing between an update campaign and swapping hardware.
The purchasing stage is the only point at which a configuration decision can solve the problem cheaply. The same questions that cause expensive rework later — encryption coverage, credential control, update capability — are answered in procurement simply by choosing a model with the right security features in the first place. Writing security items into the acceptance checklist costs less than replacing an entire batch later.
Two typical entry points cover most projects. A site that needs one serial device connected at a time starts with a compact model; a site that concentrates several serial devices into the network starts with a multi-port one.
One RS232 port plus one RS485 port, both working simultaneously, fixed inside a control cabinet for the long term: USR-TCP232-410s.Wide-range DC power, -40 to +85 °C industrial operating temperature, metal housing, hardware plus software watchdog, and a button to restore factory settings if the configuration is lost. SSL/TLS encryption covers TCP Client, HTTP Client and MQTT modes with two-way certificate authentication. The product carries CE, FCC, ROHS, WEEE and RCM certifications and serves well as a security baseline for single-point access.
Multiple ports for centralized access: USR-N520.The vendor positions it as a 2-port secure serial device server with two RS232/485 ports. SSL/TLS encryption covers the same set — TCP Client, HTTP Client and MQTT — with two-way certificate authentication. It also integrates a Modbus RTU/TCP gateway with multi-host polling, accepts DC 5-36 V input with reverse-polarity protection, and is built around an ST Cortex-M7 core. When one port or more ports are needed, the same N series offers 1-port and 4-port models as well.
Adding security items to the evaluation table is part of the purchasing process, just like checking baud rate and port count. The practical steps are straightforward: confirm that serial data travels over an encrypted link, confirm that default credentials and idle services can be changed or disabled, and confirm that the firmware has an update channel. All three answers can be found in the specification sheet and the official documentation. A practical way to close the loop is to treat these items as acceptance criteria: before a batch goes into production, verify the encrypted session, the changed credentials and the latest firmware on a sample unit. A serial to Ethernet converter is expected to run unattended at the site for years; ten minutes of verification at the selection stage saves a lot of rework after go-live.
