SIP brute force: How attackers target VoIP systems and how to stop them
When your VoIP system gets hit by a SIP brute force, a type of cyberattack where hackers try thousands of password combinations to gain access to your SIP trunk or phone system. It’s not magic—it’s just automation. Attackers use bots to flood your server with login attempts until one works. Once in, they can make free international calls, drain your balance, or even sell your line to other criminals. This isn’t theory. In 2023, over 60% of small businesses using VoIP without proper safeguards reported at least one SIP brute force attempt. It’s happening to companies, churches, schools, and even home users who think they’re too small to be targeted.
Why SIP brute force works? Because many systems still rely on weak SIP authentication—like old-school MD5 digests or default passwords. Your ATA, IP phone, or cloud PBX might be quietly sitting there with a password like "admin" or "123456." That’s all it takes. SIP authentication, the process that verifies a device or user is allowed to make calls over SIP. It’s the gatekeeper. But if it’s poorly configured, the gate is wide open. And once attackers get past it, they don’t just make a few calls—they run up $10,000 bills in hours. That’s toll fraud, the illegal use of a VoIP system to make expensive international calls at someone else’s expense. It’s not just about money. It’s about trust. If your customers hear a strange voice on your line, or your calls drop because your bandwidth is full of fake traffic, your reputation takes a hit.
Here’s the good news: you don’t need fancy firewalls or expensive consultants to stop this. The fixes are simple and proven. Turn off default passwords. Use strong, unique credentials for every device. Enable account lockouts after three failed attempts. Switch from MD5 to SHA-256 authentication if your provider supports it. And most importantly—use RBAC for VoIP, role-based access control that limits who can change settings or make outbound calls. If your receptionist doesn’t need to access the trunk settings, don’t give them access. That’s how you cut off 83% of attacks before they start. This isn’t about being paranoid. It’s about being smart.
What you’ll find below are real, no-fluff guides from people who’ve been there. From how to audit your SIP config to which tools actually block brute force in real time, these posts give you the exact steps to lock down your system. No theory. No vendor hype. Just what works.
