GXP1600 VoIP Phones Hit by Critical RCE Flaw

Cybersecurity researchers just disclosed a high-severity flaw in Grandstream's GXP1600 series VoIP phones, published today on February 18, 2026. This issue lets attackers remotely execute code without any authentication, putting networked office phones at direct risk of takeover. With remote work still common, devices like these sit on corporate networks, amplifying the threat.

The vulnerability, tracked as CVE-2026-2329, stems from a stack-based buffer overflow in the GXP1600 series. It scores 9.3 on the CVSS scale, marking it as critical. Attackers can trigger it remotely, leading to full device compromise without user interaction or credentials.

What Background Do Readers Need on VoIP Phones?

VoIP phones convert voice calls to digital packets sent over IP networks, replacing traditional analog systems. Grandstream's GXP1600 series targets small businesses and enterprises seeking cost-effective entry-level devices. These phones support SIP, the standard protocol for initiating sessions, and handle features like call forwarding, conferencing, and directory integration.

Devices in this line connect directly to Ethernet switches or routers, often behind firewalls but exposed to internal traffic. They run lightweight firmware on ARM-based processors with limited RAM and storage, typical for embedded systems. Grandstream positions the GXP1600 as reliable for daily use in reception areas or home offices, with HD audio and PoE support.

Back in the early 2010s, VoIP adoption surged as companies ditched PBX hardware for cloud-based or on-premise IP systems. Today in 2026, millions of such phones operate worldwide, integrated with platforms like Microsoft Teams or Asterisk servers. The GXP1600 series fits into this by offering multiple lines and color displays on models like the GXP1625 or GXP1620.

Security has lagged in this space. Phones process constant network traffic for provisioning, firmware updates, and signaling, creating attack surfaces. Past incidents, such as the 2018 Ring doorbell hacks, showed how compromised IoT voice devices enable eavesdropping or pivoting.

Breaking Down CVE-2026-2329 Technically

CVE-2026-2329 exploits a stack-based buffer overflow, a classic memory corruption bug. In C or C++ code—common in phone firmware—a function copies data into a fixed-size stack buffer without bounds checking. Excess input overwrites adjacent memory, including return addresses.

Attackers craft malicious packets targeting the vulnerable service, likely a web server, TR-069 provisioning interface, or SIP parser on the GXP1600. The stack holds local variables and the function's return pointer. Overflowing lets them control execution flow, jumping to shellcode or ROP chains for arbitrary code.

Unauthenticated access means no login required; any network-reachable device responds. CVSS 9.3 reflects high impact: remote attack vector, low complexity, no privileges needed, full system access, and no user interaction. Engineering tradeoffs explain this: embedded devs prioritize low latency and resource use over heavy validation, using strcpy-like functions for speed.

Stack Overflows in Embedded VoIP Firmware

VoIP firmware parses headers from UDP/TCP packets rapidly. SIP messages or HTTP requests for config can exceed buffer sizes if malformed. Grandstream's stack likely uses a small buffer, say for usernames or URIs, vulnerable to long strings.

Mitigations like stack canaries or ASLR exist but falter on resource-constrained hardware. Phones boot with fixed memory maps; randomization adds overhead. Developers face choices: allocate dynamic buffers (risking heap issues) or static ones (buffer risks). Secure coding demands snprintf, but legacy code persists.

Proof-of-concept likely sends oversized payloads via tools like Scapy. Once exploited, attackers gain root on the phone's Linux-based OS, dumping configs, sniffing RTP audio streams, or installing backdoors. From there, lateral movement to VoIP servers or VLANs follows.

How Does GXP1600 Stack Up Against Competitors?

Grandstream competes with Yealink's T4 series, Cisco's 6800/7800 lines, and Poly's VVX models. Yealink emphasizes encrypted provisioning; Cisco integrates with ISE for NAC. Grandstream focuses on affordability, shipping firmware with known vulns fixed slower than pricier rivals.

Cisco phones enforce TLS for all management, reducing unauthenticated exposure. Yealink supports auto-provisioning locks. GXP1600's open ports for HTTP/HTTPS, SNMP, and CDP mirror industry norms but lack default hardening. No source details patches, but Grandstream historically releases firmwares quarterly.

In benchmarks—not from this report—Grandstream scores well on call quality but trails in security certifications. Enterprises pick Cisco for trust, SMBs Grandstream for price. This flaw highlights why: budget devices cut validation corners.

Real-World Implications for Users and Businesses

Enterprises with GXP1600 deployments face immediate risks. Phones in call centers or executive suites process sensitive audio; compromise leaks conversations. Attackers could reroute calls, inject noise, or use devices as DDoS bots.

Most coverage misses pivot potential. A seized phone bridges voice VLANs to data networks, enabling SMB scans or ransomware drops. In 2026 hybrid setups, these integrate with UCaaS like Zoom Phone, escalating breaches.

Developers embedding VoIP should audit SIP stacks like PJSIP or Sofia-SIP for overflows. Businesses: segment networks, disable unused services. End users at home risk ISP pivots, though firewalls block most.

The risk here is widespread exposure. Grandstream sells thousands yearly; unpatched fleets invite scans via Shodan, which indexes web-facing phones. CVSS 9.3 demands priority over routine updates.

What Should Organizations Do Immediately?

Isolate GXP1600 devices on separate VLANs with ACLs blocking inbound management traffic. Monitor for anomalous firmware fetches or SIP floods. Check Grandstream's site for patches—researchers disclosed responsibly, so fixes may drop soon.

Run Nmap scans: open ports like 80, 443, 5060 signal exposure. Tools like Nessus detect CVEs. For devs, fuzz SIP endpoints with Bohrium or SIPVicious. This likely means firmware audits across vendors.

Frequently Asked Questions

What is CVE-2026-2329?

CVE-2026-2329 is a critical stack-based buffer overflow in Grandstream GXP1600 VoIP phones. It enables unauthenticated remote code execution with a CVSS score of 9.3. Disclosed February 18, 2026, by researchers via The Hacker News.

Which devices are affected?

The Grandstream GXP1600 series, including models like GXP1620 and GXP1625. Any firmware version prior to a patch remains vulnerable. Check your device's admin page for series confirmation.

How do attackers exploit this?

By sending crafted network packets to trigger the buffer overflow. No authentication or interaction needed; remote access suffices. Leads to code execution, potentially full compromise.

Is there a patch available?

As of February 18, 2026, no patch details in disclosures. Monitor Grandstream's support portal for firmware updates. Apply promptly once released.

Who should worry most?

Businesses with GXP1600 on corporate networks, especially call centers or remote setups. Home users face lower but real risks from exposed ports.

Grandstream must accelerate secure-by-design firmware, perhaps adopting memory-safe languages like Rust for parsers. Watch for exploit code on GitHub or Metasploit modules in coming weeks. Enterprises should reassess VoIP vendors, prioritizing those with rapid disclosure timelines. If unpatched, expect targeted attacks by Q2 2026.