CVE-2026-7273: Zyxel GS1900-48HPv2 Stack Buffer Overflow RCE Vulnerability

Technical summary

CVE-2026-7273 is a stack-based buffer overflow (CWE-121) in the CGI application layer of the Zyxel GS1900-48HPv2 managed switch. The vulnerability exists in firmware versions through 2.90(ABTQ.1)C0 and allows stack memory corruption via a malformed HTTP request. Successful exploitation leads to arbitrary OS command execution in the context of the web server process, typically with elevated privileges on the switch. The attack vector is adjacent network (AV:A), requires no user interaction, and bypasses all authentication controls.

Business impact

Compromise of a Zyxel GS1900-48HPv2 switch in your network infrastructure could lead to unauthorized access to all traffic passing through the device, modification of network configurations, deployment of persistent backdoors, and potential lateral movement into connected systems. In environments where these switches manage critical network segments—such as data center core switches or distribution layer switches—the business impact extends to confidentiality breaches, operational downtime, and regulatory exposure if sensitive data transits the compromised device.

Affected systems

Zyxel GS1900-48HPv2 managed switches running firmware versions through 2.90(ABTQ.1)C0 are affected. Only units accessible from the local network are at direct risk; however, if the switch is reachable from a compromised host on that network segment, remote exploitation becomes possible. Organizations should inventory all GS1900-48HPv2 units and verify their current firmware version immediately.

Exploitability

This vulnerability is readily exploitable by attackers with network adjacency—no authentication is required and no user interaction is necessary. The attack is deterministic and likely requires minimal resources to craft. While currently not listed in CISA's Known Exploited Vulnerabilities catalog, the straightforward nature of HTTP-based buffer overflow attacks and the lack of authentication requirements suggest active exploitation risk is high if the vulnerability becomes publicly weaponized.

Remediation

Vendors should release and apply a firmware patch that addresses the stack buffer overflow in the CGI module. Users must upgrade affected switches to a patched firmware version when available from Zyxel. Until patching is possible, implement strong network segmentation to restrict which systems can reach the management interface of these switches, and monitor for anomalous HTTP requests directed at the CGI application. Disable remote management access if not required.

Patch guidance

Verify the current firmware version of each Zyxel GS1900-48HPv2 unit via the administrative web interface (System > Software) and compare against the affected version range (through 2.90(ABTQ.1)C0). Monitor Zyxel's security advisory and product support pages for release of a patched firmware version. Once a patch is available, test it in a non-production environment, then schedule controlled firmware updates during a maintenance window. Ensure automatic factory configuration restore is disabled during the update to preserve existing settings.

Detection guidance

Monitor HTTP access logs on the switch management interface for unusual request patterns, particularly long or malformed HTTP headers and payloads targeting the CGI application. Network-based detection can identify suspicious HTTP requests with abnormal sizes or character sequences directed at the switch's web interface. Endpoint detection on systems with access to the switch can flag unexpected process creation or OS command execution originating from the switch IP. Baseline normal management traffic and alert on deviations.

Why prioritize this

This vulnerability scores 8.8 (HIGH severity) due to the combination of unauthenticated local network access, direct OS command execution capability, and impact on all three security properties (confidentiality, integrity, availability). While KEV listing is not yet confirmed, the lack of authentication barriers and the criticality of network infrastructure make this a top-tier patching priority. Organizations operating these switches in production environments should treat this as urgent.

Risk score, explained

The CVSS 3.1 score of 8.8 reflects Attack Vector: Adjacent (network-local access required), Attack Complexity: Low (straightforward exploitation), Privileges Required: None (unauthenticated), User Interaction: None (automatic). The impact metrics are all set to High, indicating complete compromise of confidentiality, integrity, and availability. The score is elevated by the practical ease of exploitation, absence of authentication, and the trusted role network switches play in infrastructure.

Frequently asked questions