CVE-2026-2329 Overview
An unauthenticated stack-based buffer overflow vulnerability exists in the HTTP API endpoint /cgi-bin/api.values.get of Grandstream GXP1600 series VoIP phones. A remote attacker can leverage this vulnerability to achieve unauthenticated remote code execution (RCE) with root privileges on a target device. This critical firmware vulnerability affects all six device models in the GXP1600 series and requires no authentication to exploit.
Critical Impact
Unauthenticated remote attackers can achieve complete device compromise with root-level code execution on vulnerable Grandstream VoIP phones via network-accessible HTTP API.
Affected Products
- Grandstream GXP1610
- Grandstream GXP1615
- Grandstream GXP1620
- Grandstream GXP1625
- Grandstream GXP1628
- Grandstream GXP1630
Discovery Timeline
- 2026-02-18 - CVE-2026-2329 published to NVD
- 2026-02-18 - Last updated in NVD database
Technical Details for CVE-2026-2329
Vulnerability Analysis
This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), a memory corruption flaw that occurs when data written to a stack-allocated buffer exceeds its intended size. In the context of CVE-2026-2329, the vulnerable endpoint /cgi-bin/api.values.get fails to properly validate the length of user-supplied input before copying it to a fixed-size buffer on the stack.
The network-accessible nature of this vulnerability is particularly concerning for enterprise environments where VoIP phones are commonly deployed. Since the HTTP API endpoint requires no authentication, any attacker with network access to the device can craft malicious requests to trigger the overflow condition. Successful exploitation overwrites critical stack data including the return address, allowing attackers to redirect program execution to arbitrary code.
Root Cause
The root cause is insufficient input validation in the HTTP API handler for the /cgi-bin/api.values.get endpoint. The vulnerable code path accepts user-controlled data via HTTP requests and copies this data into a stack-allocated buffer without proper bounds checking. This classic stack buffer overflow pattern allows attackers to write beyond the buffer's boundary, corrupting adjacent stack memory including saved return addresses and other control data.
Attack Vector
The attack vector is network-based with no authentication required. An attacker can exploit this vulnerability by sending a specially crafted HTTP request to the /cgi-bin/api.values.get endpoint containing an oversized payload. The payload overflow corrupts the stack, and by carefully controlling the overflow data, an attacker can achieve arbitrary code execution with root privileges. The low attack complexity and lack of required user interaction make this vulnerability particularly dangerous for internet-exposed or poorly segmented VoIP deployments.
A Metasploit module has been developed for this vulnerability, as indicated by the GitHub Metasploit Pull Request. This significantly lowers the barrier to exploitation, making immediate patching critical for affected organizations.
Detection Methods for CVE-2026-2329
Indicators of Compromise
- Unusual HTTP requests to /cgi-bin/api.values.get with abnormally large parameter values or request bodies
- Unexpected network connections originating from GXP1600 series VoIP phones to external IP addresses
- Device crashes, reboots, or unexpected behavior following HTTP requests to the API endpoint
- Signs of reverse shell connections or unauthorized remote access sessions from VoIP phone IP addresses
Detection Strategies
- Implement network-based intrusion detection rules to monitor for oversized HTTP requests to Grandstream device API endpoints
- Deploy web application firewall (WAF) rules to block requests with excessively long parameters targeting /cgi-bin/api.values.get
- Monitor network traffic for unusual patterns from VoIP phone subnets, including outbound connections on unexpected ports
- Analyze HTTP access logs for repeated requests to vulnerable endpoints from suspicious source addresses
Monitoring Recommendations
- Enable comprehensive logging on network devices monitoring VoIP traffic segments
- Configure SIEM alerts for anomalous HTTP request patterns targeting embedded device management interfaces
- Establish baseline network behavior for VoIP phones and alert on deviations indicating potential compromise
- Monitor for firmware modification attempts or unauthorized configuration changes on GXP1600 devices
How to Mitigate CVE-2026-2329
Immediate Actions Required
- Update all Grandstream GXP1600 series devices to firmware version 1.0.7.81 or later immediately
- Isolate vulnerable VoIP phones on dedicated network segments with restricted internet access
- Implement network access controls to limit which systems can communicate with VoIP phone management interfaces
- Audit network configurations to ensure VoIP devices are not directly exposed to untrusted networks
Patch Information
Grandstream has released a security patch addressing this vulnerability. Organizations should update to firmware version 1.0.7.81 or later as documented in the Grandstream Firmware Release Notes. Additional security advisories and guidance are available through the Grandstream PSIRT Portal. For detailed technical analysis of this vulnerability, refer to the Rapid7 Blog CVE-2026-2329 Analysis.
Workarounds
- Implement strict network segmentation to prevent untrusted systems from accessing VoIP phone management interfaces
- Deploy firewall rules blocking external access to HTTP/HTTPS ports on GXP1600 series devices
- Configure access control lists (ACLs) to restrict management interface access to authorized administrative workstations only
- Consider disabling the HTTP management interface if not required for operational purposes
# Example firewall rule to restrict access to VoIP phone management (iptables)
# Replace 192.168.10.0/24 with your VoIP subnet and 10.0.0.5 with admin workstation IP
iptables -A FORWARD -d 192.168.10.0/24 -p tcp --dport 80 -s ! 10.0.0.5 -j DROP
iptables -A FORWARD -d 192.168.10.0/24 -p tcp --dport 443 -s ! 10.0.0.5 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
