Critical Grandstream VoIP Bug Highlights SMB Security Blind Spot
Critical Grandstream VoIP Bug Highlights SMB Security Blind Spot
A critical security vulnerability in a Voice over Internet Protocol (VoIP) phone deployed in small and midsized businesses (SMBs), hotels, call centers, and other organizations globally has underscored the risks in treating voice infrastructure as a utility rather than an IT asset. The buffer-overflow flaw, tracked as CVE-2026-2329, affects all six models of Grandstream Networks’ GXP1600 series VoIP phones and carries a severity rating of 9.3 out of 10 on the CVSS scale. The vulnerability allows unauthenticated cyberattackers to take complete control of affected devices and execute remote code. 🚨
A security researcher at Rapid7 discovered the vulnerability during a zero-day research project targeting the GXP1600 series and reported it to Grandstream in early January. The vendor publicly disclosed the issue this week, after Grandstream released a patch for the flaw on Feb. 2. “In the worst-case scenario, an unauthenticated attacker can leverage CVE-2026-2329 to achieve remote code execution (RCE) with root privileges on a target device,” says Stephen Fewer, senior principal security researcher at Rapid7, who discovered the bug. From there, the attacker can extract credentials, such as user accounts and SIP accounts, including plaintext passwords that are stored on the device.
VoIP phones can be attractive targets for attackers because they function as fully networked computers in a business environment, but often with very little security oversight. As Fewer points out, organizations often tend to implicitly trust VoIP phones and leave them mostly unmonitored and untended for years. As Randolph Barr, chief information security officer (CISO) at Cequence Security, notes, “VoIP phones are an attractive but underappreciated attack surface.” Unlike laptops and servers, they often sit outside formal endpoint security, logging, and patch management programs. With root-level access, an attacker can intercept calls, commit toll fraud, and impersonate users, Barr says. More concerning, the device can become a network foothold, used to scan internal systems, attempt lateral movement, or quietly beacon out as a command-and-control node.
All of these issues are particularly relevant for small and medium-sized businesses because they often don’t have good network separation, Barr points out. Instead, they may have flat networks where phones and computers share the same VLAN, and have no firewalls and few access controls. Defenders should view firmware-level RCE as high impact but low frequency, and prioritize strong authentication, segmentation, and timely patching accordingly. Fewer recommended organizations should always keep VoIP device firmware updated to the latest version, harden their SIP infrastructure by using TLS and secure key exchange mechanisms, and ensure that VoIP infrastructure is deployed within isolated network segments or VLANs.