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CVE-2026-7273 is a stack-based buffer overflow vulnerability (CWE-121) that resides in the CGI program of the Zyxel GS1900 series switch firmware. The flaw affects the GS1900-48HPv2 model running firmware versions up to and including 2.90(ABTQ.1)C0. An attacker who is positioned on the same local area network (LAN) as the vulnerable device can exploit this issue without any authentication. The vulnerability is triggered when the CGI program processes a specially crafted HTTP request. Because the program fails to properly validate the length of user-supplied input before copying it into a fixed-size stack buffer, an oversized request can overwrite adjacent memory on the stack. This memory corruption allows the attacker to control the execution flow of the CGI process. Successful exploitation can lead to the execution of arbitrary operating system commands with the privileges of the CGI service. The CVSS v3.1 score for this vulnerability is 8.8, which is rated as HIGH severity. The vector string is CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H, indicating that the attack vector is adjacent (LAN-based), the attack complexity is low, no privileges are required, and no user interaction is needed. The impact to confidentiality, integrity, and availability is high. Zyxel has released firmware updates to address this issue. The patched version for the GS1900-48HPv2 is 2.90(ABTQ.2)C0. Users are strongly advised to upgrade their devices to the fixed firmware as soon as possible. In the absence of a patch, restricting LAN access to the switch management interface can reduce the attack surface. The vulnerability was reported to Zyxel by researchers from ISCAS.
DailyCVE Form:
Platform: Zyxel GS1900
Version: 2.90(ABTQ.1)C0
Vulnerability : Stack overflow
Severity: High
date: 2026-06-16
Prediction: 2026-06-12
What Undercode Say:
Analytics
Check firmware version of a Zyxel GS1900 switch via HTTP curl -s http://<switch-ip>/cgi-bin/luci/ | grep -i "version" Extract the firmware version string from the device response curl -s http://<switch-ip>/cgi-bin/dispatcher.cgi | strings | grep -E "2.90(ABTQ" Verify the patch level by comparing the version suffix Vulnerable: 2.90(ABTQ.1)C0 Patched: 2.90(ABTQ.2)C0
// Simplified representation of the vulnerable CGI buffer handling
void handle_request(char input) {
char buffer[bash]; // fixed-size stack buffer
strcpy(buffer, input); // no bounds check — overflow occurs
}
How Exploit: (Educational Purposes!)
Conceptual demonstration of sending an oversized HTTP request
to a vulnerable CGI endpoint on the GS1900-48HPv2 switch.
This is for educational purposes only.
python3 - <<'EOF'
import requests
target = "http://192.168.1.100/cgi-bin/vulnerable_endpoint.cgi"
payload = b"A" 1024 overflow the stack buffer
try:
r = requests.post(target, data=payload, timeout=5)
print(f"Response status: {r.status_code}")
print(f"Response length: {len(r.content)}")
except Exception as e:
print(f"Request failed: {e}")
EOF
Protection: from this CVE
– Update the GS1900-48HPv2 firmware to version 2.90(ABTQ.2)C0 or later.
– Restrict management interface access to trusted IP addresses using ACLs.
– Isolate the switch management VLAN from general user traffic.
– Monitor network traffic for unusually large HTTP requests to CGI endpoints.
– Apply the official Zyxel security advisory patches for all affected GS1900 models.
Impact:
- Unauthenticated remote code execution on the switch.
- Full compromise of confidentiality, integrity, and availability.
- Potential lateral movement within the local network.
- Device takeover and persistent backdoor installation.
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Sources:
Reported By: www.cve.org
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