Introduction: A Diagnosis Gone Wrong
I was just checking the temperature of my Synology DS1621xs+ hard drives. I’d heard that every additional 10 °C raised a disk’s failure risk by about 23 %. Opening DSM, I thought I was simply monitoring fans. Instead, I uncovered an invisible blight: more than 40 hours of repeated login attempts.
Early Signs of Intrusion
The Log Center displayed a series of identical failure messages, each with a different IP address—a pattern I’d never seen before. Investigation revealed the attempts occurred every 10 to 40 seconds.
1. NAS Technical Context and Default Security
My home lab was behind a CGNAT, and I used Tailscale for secure remote access. I had disabled unnecessary services, updated DSM, and enabled the built‑in firewall.
Despite these precautions, the NAS remained exposed to automated attacks due to an overlooked setting in my own automation script. The issue wasn’t a known Synology vulnerability but a “backdoor” I’d left active.
2. Log Analysis: An Alarming Pattern
Each Log Center entry read something like: User [admin] from [IP] failed to sign in to [DSM] via [password]. Alternate usernames—marketing, muhasebe, melvin, charlene—were brute‑force trials. None used my real username.
The log table shows the first attempt on September 26 at 20:38 and continued until September 28 at 03:17, with a regular cadence of 10–40 seconds. This rhythm indicates an automated script rather than a human.
3. Potential Consequences of a Successful Attack
A successful credential stuffing could grant unauthorized access to all NAS data: photos, sensitive documents, server backups. Additionally, fan control could be hijacked to induce overheating, raising failure probability.
Loss of log integrity and authentication compromise are major threats in a home environment where off‑site backups aren’t always secured.
4. Immediate Corrective Measures
I disabled the malicious script, removed unused accounts, and enabled two‑factor authentication (2FA) via Tailscale. I also set an attempt threshold: after 5 consecutive failures, the IP is blocked for 30 minutes.
- Enable DSM firewall
- Update Synology firmware
- Use complex passwords (12 alphanumeric characters + symbols)
- Monitor logs daily
Setting Up a Notification System
I configured a Slack webhook to receive an alert whenever a login attempt fails, enabling rapid response before the attack escalates.
5. Best Practices to Protect Your NAS
1. Limit exposed services: disable SSH, Telnet, or FTP if not needed.
2. Use a dedicated VPN instead of direct Tailscale access.
3. Implement password rotation policy (at least every 90 days).
4. Enable hardware monitoring: real‑time alerts for temperature and fan speed.
“NAS security isn’t just about firewalls; it also depends on daily vigilance of logs.” — Synology cybersecurity expert
Conclusion: Protect Your NAS Before It’s Too Late
This experience highlighted that even a home device can become a target for automated attacks. By applying the measures above, you dramatically reduce compromise risk and ensure your data’s longevity.
Don’t let your NAS be the next credential‑stuffing victim—implement these best practices today and stay vigilant. Protect your data, secure your NAS.
