Rapid7 researchers have disclosed a critical vulnerability in Grandstream’s GXP1600 series VoIP desk phones that could allow attackers to remotely eavesdrop on conversations, raising fresh concerns about the security posture of commonly deployed office telephony.
The flaw, tracked as CVE-2026-2329, is described as a stack-based buffer overflow that can be exploited without authentication. According to Rapid7, a remote attacker could gain root access to affected devices, potentially enabling modification of call routing, interception of audio streams, and persistent, covert monitoring of phone activity.
Unlike many endpoint vulnerabilities that require user interaction, this issue is accessible over the network, significantly lowering the barrier to exploitation where devices are exposed. Once compromised, a phone could effectively be converted into a listening device without the knowledge of users.
Rapid7 notes that VoIP desk phones are frequently treated as low-risk infrastructure appliances rather than networked computing devices. In many small and medium-sized businesses (SMBs), they are deployed on internal networks, infrequently patched, and implicitly trusted. That combination — network accessibility, limited monitoring, and inconsistent update cycles — can make them attractive espionage targets.
The GXP1600 series is widely used in SMB environments due to its affordability and ease of deployment. In such settings, VoIP handsets are often integrated into flat internal networks without strict segmentation, meaning compromise of a single device could provide lateral movement opportunities or serve as a foothold for broader intrusion.
According to the technical advisory, exploitation of CVE-2026-2329 could allow an attacker to:
- Execute arbitrary code with root privileges
- Modify SIP configuration and call handling behaviour
- Intercept or redirect voice traffic
- Maintain persistence on the device
While no active exploitation campaigns have been publicly confirmed at the time of disclosure, the severity rating reflects both the lack of authentication requirement and the potential impact on confidentiality.
Grandstream has released a firmware update to address the vulnerability. Organisations using affected models are being urged to apply patches promptly, audit their VoIP exposure, and review network configurations. Security practitioners also recommend verifying whether administrative interfaces are exposed to the internet, restricting management access, and ensuring VoIP devices are isolated through VLAN segmentation or firewall controls.
The disclosure serves as a reminder that IP-based telephony systems are part of the broader enterprise attack surface. As voice traffic increasingly converges with data networks, vulnerabilities in desk phones can present risks comparable to those in servers or workstations.
For SMBs in particular — which may lack dedicated VoIP security oversight — the incident highlights the need to include telephony assets in asset inventories, patch management programs, and vulnerability scanning routines.
Rapid7’s analysis frames the issue as a modern analogue to historical wiretapping: instead of physical access to copper lines, attackers can exploit software flaws in network-connected devices. The technical shift underscores a wider security reality — if a device runs firmware and connects to an IP network, it should be treated as a potential entry point, not a passive appliance.
