WA300 5.2cu.7112_B20190227 — CraftedSignal Threat Feed

Totolink WA300 Buffer Overflow Vulnerability (CVE-2026-7719)

hello@craftedsignal.io — Mon, 04 May 2026 02:15:58 +0000

A critical buffer overflow vulnerability, identified as CVE-2026-7719, has been discovered in Totolink WA300 version 5.2cu.7112_B20190227. This vulnerability resides within the loginauth function of the /cgi-bin/cstecgi.cgi file, affecting the POST Request Handler component. The vulnerability is triggered by manipulating the http_host argument in a POST request. The exploit is publicly available, increasing the risk of widespread exploitation. This vulnerability allows for remote code execution, potentially granting attackers full control over the affected device. The affected version was released in February 2019. Defenders should prioritize patching or mitigating this vulnerability to prevent potential compromise.

Attack Chain

The attacker identifies a vulnerable Totolink WA300 device running firmware version 5.2cu.7112_B20190227.
The attacker crafts a malicious HTTP POST request targeting the /cgi-bin/cstecgi.cgi endpoint.
The crafted POST request includes a specially crafted http_host argument designed to overflow the buffer in the loginauth function.
The vulnerable loginauth function processes the http_host argument without proper bounds checking.
The oversized http_host argument overwrites adjacent memory regions, including the return address on the stack.
Upon completion of the loginauth function, the overwritten return address is used, redirecting execution to attacker-controlled code.
The attacker-controlled code executes with elevated privileges, allowing the attacker to execute arbitrary commands on the device.
The attacker gains complete control of the device, potentially using it for malicious purposes such as botnet participation, data theft, or further network penetration.

Impact

Successful exploitation of CVE-2026-7719 allows a remote attacker to execute arbitrary code on the vulnerable Totolink WA300 device. This can lead to complete device compromise, allowing the attacker to steal sensitive information, use the device as a botnet node, or pivot to other devices on the network. Given the public availability of the exploit, widespread exploitation is possible, potentially affecting a large number of home and small business networks using the vulnerable device.

Recommendation

Deploy the Sigma rule Detect Totolink WA300 HTTP Host Buffer Overflow Attempt to identify exploitation attempts in web server logs.
Monitor web server logs for POST requests to /cgi-bin/cstecgi.cgi with unusually long http_host headers.
Consider deploying a web application firewall (WAF) rule to filter out malicious requests targeting CVE-2026-7719.
Upgrade to a patched version of the firmware or replace the affected device to remediate the vulnerability.

Totolink WA300 Buffer Overflow Vulnerability in UploadCustomModule

hello@craftedsignal.io — Mon, 04 May 2026 01:16:05 +0000

A buffer overflow vulnerability has been identified in Totolink WA300 wireless router, specifically version 5.2cu.7112_B20190227. The vulnerability resides within the UploadCustomModule function of the /cgi-bin/cstecgi.cgi file, a component of the POST Request Handler. The identified vulnerability allows a remote attacker to cause a buffer overflow through manipulation of the File argument within a crafted POST request. Public proof-of-concept exploit code is available, increasing the likelihood of exploitation. This vulnerability poses a significant risk, as successful exploitation could lead to arbitrary code execution, potentially allowing attackers to fully compromise affected devices. Defenders should prioritize detection and mitigation strategies to prevent exploitation.

Attack Chain

Attacker identifies a vulnerable Totolink WA300 device running firmware version 5.2cu.7112_B20190227.
Attacker crafts a malicious POST request targeting the /cgi-bin/cstecgi.cgi endpoint.
The POST request includes a File argument with a payload exceeding the buffer size allocated for the UploadCustomModule function.
The UploadCustomModule function processes the POST request without proper bounds checking on the File argument.
The oversized File argument overwrites adjacent memory regions, including potentially critical program data and control flow instructions.
The buffer overflow allows the attacker to inject and execute arbitrary code on the device.
The attacker gains remote shell access to the device with elevated privileges.
The attacker could then use the compromised device to pivot into the internal network or cause a denial-of-service condition.

Impact

Successful exploitation of this buffer overflow vulnerability can lead to complete compromise of the affected Totolink WA300 device. An attacker could gain unauthorized access to the device’s configuration, intercept network traffic, or use the device as a bot in a larger attack. Given the high CVSS score of 8.8, the impact is considered critical. Home and small business networks using the affected router model are at risk. The vulnerability allows for remote code execution, leading to significant potential for damage.

Recommendation

Deploy the Sigma rule Detect Totolink WA300 UploadCustomModule Buffer Overflow Attempt to detect malicious POST requests targeting the vulnerable endpoint.
Monitor web server logs for POST requests to /cgi-bin/cstecgi.cgi with unusually large File parameters, as indicated in the Sigma rule.
Apply any available firmware updates from Totolink to patch CVE-2026-7717 if they become available.
Implement network segmentation to limit the impact of a compromised router on other internal network resources.