Six Grandstream GXP1600-series phones running firmware versions up to and including 1.0.7.80 are affected by CVE-2026-2329, a critical flaw that can let an unauthenticated remote attacker take control of a phone with root privileges. Grandstream firmware 1.0.7.81, released January 31, 2026, is the stated security-fix boundary; upgrade affected phones to that version or later.
What is CVE-2026-2329?
CVE-2026-2329 is a stack-based buffer overflow in the web API of Grandstream GXP1600-series VoIP phones. Rapid7 Labs says an attacker can exploit it without logging in to execute code remotely with root privileges. Rapid7 also reports that the vulnerable interface is reachable in the default configuration it describes.
The National Institute of Standards and Technology (NIST) classifies the weakness as CWE-121 and gives it a CVSS 4.0 base score of 9.3, rated Critical. The combination of remote access and root-level control makes this a serious issue for organizations using affected phones.
Which Grandstream phones are affected?
The affected models are the following six GXP1600-series handsets:
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| Model | Vulnerability status |
|---|---|
| GXP1610 | Affected on firmware up to and including 1.0.7.80 |
| GXP1615 | Affected on firmware up to and including 1.0.7.80 |
| GXP1620 | Affected on firmware up to and including 1.0.7.80 |
| GXP1625 | Affected on firmware up to and including 1.0.7.80 |
| GXP1628 | Affected on firmware up to and including 1.0.7.80 |
| GXP1630 | Affected on firmware up to and including 1.0.7.80 |
NIST lists versions through 1.0.7.80 as affected. Grandstream’s GXP16xx release note identifies version 1.0.7.81, dated January 31, 2026, as the release that fixed security vulnerabilities.
Can someone listen to calls on a vulnerable phone?
The vulnerability creates a credible route to call interception, but that is not the same as evidence that a particular phone was compromised. An attacker with root-level control could tamper with telephony software or SIP settings. That control could expose call audio, SIP signaling, and credentials, and could enable stealthy eavesdropping.
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The sources cited for this issue do not establish that every vulnerable phone was exploited, or give a verified count of affected organizations, devices, or intercepted calls. A vulnerable version indicates risk, not proof that calls were monitored.
How to check and secure a GXP1600 phone
- Identify each handset. Check the model label or your phone inventory for GXP1610, GXP1615, GXP1620, GXP1625, GXP1628, or GXP1630.
- Record its firmware version. Check the phone’s administration interface or your organization’s provisioning or device-management system. Compare the installed version with the affected range above.
- Upgrade affected phones. Obtain firmware through Grandstream’s official firmware source and install version 1.0.7.81 or later. Follow the vendor’s instructions for the model and deployment method.
- Limit management exposure while addressing the issue. Restrict access to phone management interfaces to trusted administrative networks where possible. This reduces exposure but does not replace installing the security fix.
- Review configuration after updating. Check SIP credentials, provisioning settings, call-routing rules, and logs for unauthorized changes. If anything is suspicious, investigate and reset affected credentials and settings.
- Plan for phones that cannot be upgraded. Remove them from exposed networks and arrange replacement with a supported handset.
Grandstream advises customers to deploy the latest available firmware for security patches and performance updates. Keep the fleet on current supported firmware rather than treating this one update as the end of maintenance.
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What to prioritize in a phone fleet
For a business with multiple handsets, prioritize phones still running affected firmware, especially where management interfaces are exposed beyond trusted administrative networks. Track firmware and model centrally so that updates, credential changes, and any replacements can be verified rather than handled as one-off fixes.
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- Firmware support: Confirm that the device can run the security-fix release and remains supported.
- Network exposure: Determine whether its web management interface is reachable from untrusted networks.
- Credential control: Ensure SIP credentials can be rotated if suspicious changes are found.
- Lifecycle and replacement: For an unupgradable phone, consider vendor support status, replacement cost, and how easily the organization can manage the replacement centrally.
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