Zyxel GS1900 switches: out-of-bounds write in the CGI parameter parser that the exploit behind the CVE-2026-7273 KEV listing targets, fixed in the .3C0 builds

Adversaries may obtain and abuse credentials of a default account as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion. Default accounts are those that are built-into an OS, such as the Guest or Administrator accounts on Windows systems. Default accounts also include default factory/provider set accounts on other types of systems, software, or devices, including the root user account in AWS, the root user account in ESXi, and the default service account in Kubernetes.

Evidence: 2026-09-22/cve-2026-7273-zyxel-gs1900-red-heron-kev-exploited · ATT&CK page ↗

Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network. The weakness in the system can be a software bug, a temporary glitch, or a misconfiguration.

Evidence: 2026-09-22/cve-2026-7273-zyxel-gs1900-red-heron-kev-exploited · ATT&CK page ↗

Adversaries may abuse Unix shell commands and scripts for execution. Unix shells are the primary command prompt on Linux, macOS, and ESXi systems, though many variations of the Unix shell exist (e.g. sh, ash, bash, zsh, etc.) depending on the specific OS or distribution. Unix shells can control every aspect of a system, with certain commands requiring elevated privileges.

Evidence: 2026-09-22/cve-2026-7273-zyxel-gs1900-red-heron-kev-exploited · ATT&CK page ↗

Adversaries may obtain and abuse credentials of a default account as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion. Default accounts are those that are built-into an OS, such as the Guest or Administrator accounts on Windows systems. Default accounts also include default factory/provider set accounts on other types of systems, software, or devices, including the root user account in AWS, the root user account in ESXi, and the default service account in Kubernetes.

Evidence: 2026-09-22/cve-2026-7273-zyxel-gs1900-red-heron-kev-exploited · ATT&CK page ↗

Adversaries may obtain and abuse credentials of a default account as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion. Default accounts are those that are built-into an OS, such as the Guest or Administrator accounts on Windows systems. Default accounts also include default factory/provider set accounts on other types of systems, software, or devices, including the root user account in AWS, the root user account in ESXi, and the default service account in Kubernetes.

Evidence: 2026-09-22/cve-2026-7273-zyxel-gs1900-red-heron-kev-exploited · ATT&CK page ↗

Adversaries may obtain and abuse credentials of a default account as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion. Default accounts are those that are built-into an OS, such as the Guest or Administrator accounts on Windows systems. Default accounts also include default factory/provider set accounts on other types of systems, software, or devices, including the root user account in AWS, the root user account in ESXi, and the default service account in Kubernetes.

Evidence: 2026-09-22/cve-2026-7273-zyxel-gs1900-red-heron-kev-exploited · ATT&CK page ↗

Adversaries may search local system sources, such as file systems, configuration files, local databases, virtual machine files, or process memory, to find files of interest and sensitive data prior to Exfiltration.

Evidence: 2026-09-22/cve-2026-7273-zyxel-gs1900-red-heron-kev-exploited · ATT&CK page ↗

Adversaries may stage collected data in a central location or directory on the local system prior to Exfiltration. Data may be kept in separate files or combined into one file through techniques such as Archive Collected Data. Interactive command shells may be used, and common functionality within cmd and bash may be used to copy data into a staging location.

Evidence: 2026-09-22/cve-2026-7273-zyxel-gs1900-red-heron-kev-exploited · ATT&CK page ↗

Adversaries may transfer tools or other files from an external system into a compromised environment. Tools or files may be copied from an external adversary-controlled system to the victim network through the command and control channel or through alternate protocols such as ftp. Once present, adversaries may also transfer/spread tools between victim devices within a compromised environment (i.e. Lateral Tool Transfer).

Evidence: 2026-09-22/cve-2026-7273-zyxel-gs1900-red-heron-kev-exploited · ATT&CK page ↗