A high-severity stack-based buffer overflow vulnerability has been publicly disclosed in the Belkin F9K1122 wireless router, tracked as CVE-2026-5608.
Published on April 6, 2026, the flaw carries a CVSS v2 base score of 9.0 (HIGH) and a CVSS v3.1 score of 8.8 (HIGH), making it one of the more critical consumer router vulnerabilities disclosed this year.
With a working exploit already circulating in the public domain and no response from the vendor, this vulnerability poses a direct and immediate threat to anyone still running the affected firmware.
Belkin F9K1122 Buffer Overflow Flaw
At its core, CVE-2026-5608 is a stack-based buffer overflow (CWE-121) residing in the formWlanSetup function, accessible via the web interface endpoint /goform/formWlanSetup on Belkin F9K1122 devices running firmware version 1.00.33. The vulnerability is triggered by manipulating the webpage argument passed to this function.
When an oversized or specially crafted input is submitted, it overwrites memory on the stack beyond the allocated buffer boundary, a classic CWE-119 memory safety violation. Stack-based buffer overflows of this nature are particularly dangerous because the stack holds return addresses and saved registers.
By overwriting these values with attacker-controlled data, a threat actor can redirect execution flow to arbitrary shellcode or ROP (Return-Oriented Programming) gadgets, ultimately achieving remote code execution (RCE) on the device.
The attack vector is network-based and low-complexity, meaning no special configuration or unusual conditions are required to exploit the flaw.
The attacker does require low-level authentication (a standard user credential). Still, in environments where default credentials remain unchanged, a disturbingly common scenario with consumer-grade routers, this barrier is trivial to bypass.
CVSS Scoring Breakdown
The vulnerability has been assessed across three CVSS versions:
- CVSS v2.0: Base Score 9.0 (HIGH) – AV:N/AC:L/Au:S/C:C/I:C/A:C with an exploitability score of 8.0 and an impact score of 10.0
- CVSS v3.1: Base Score 8.8 (HIGH) – AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CVSS v4.0: Base Score 7.4 (HIGH) – AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H
All three scoring frameworks consistently rate the impact on confidentiality, integrity, and availability as HIGH, reinforcing the severity of successful exploitation.
A compromised router could allow attackers to intercept network traffic, pivot into internal networks, modify DNS settings for phishing campaigns, or deploy persistent backdoors.
Public Exploit and No Vendor Response
One of the most alarming aspects of this disclosure is that a proof-of-concept (PoC) exploit is already publicly available, hosted on GitHub in the repository Litengzheng/vul_db.
The researcher documented their findings under the path /Belkin/vul_80/README.md, providing technical details that significantly lower the bar for less-skilled threat actors, commonly referred to as script kiddies, to attempt exploitation at scale.
The situation is compounded by the fact that Belkin was contacted before public disclosure, but did not respond. This lack of vendor engagement is a significant concern in the security community.
Responsible disclosure practices typically involve a 90-day window for vendors to develop and release patches before public disclosure.
When vendors fail to engage, researchers are left with the difficult choice of either indefinitely suppressing critical findings or releasing information to pressure action. In this case, the vulnerability has been disclosed without a corresponding patch, leaving users in a precarious position.
This vulnerability is also tracked under the alternative identifier EUVD-2026-19146 in the ENISA European Vulnerability Database, signaling that European regulatory and security bodies are monitoring this disclosure.
Affected Products and Scope
The confirmed affected product is the Belkin F9K1122 running firmware version 1.00.33. The F9K1122 is a dual-band N900 wireless router that, while not a current-generation device, remains deployed in homes and small offices, particularly in regions where hardware refresh cycles are infrequent.
The router’s administrative web interface, as an attack surface, means any device with remote management exposed to the internet, or even accessible from within a compromised LAN segment, is at risk.
Users who have not updated or patched their router firmware, or who still rely on Belkin’s legacy device lineup, should treat this disclosure with urgency.
Recommended Mitigations
Given the absence of an official patch, network defenders and home users should take the following precautionary steps immediately:
- Disable remote management on the router’s web interface if it is not strictly necessary, preventing external network access to the vulnerable endpoint
- Restrict LAN access to the admin panel by binding it to specific trusted IP addresses or MAC addresses, where possible
- Change default credentials to strong, unique passwords to raise the authentication barrier for exploitation
- Monitor for anomalous traffic originating from the router, including unexpected DNS changes or outbound connections to unfamiliar IPs
- Consider replacing the device with a currently supported router model that receives active security updates, as legacy firmware without vendor support remains an indefinite liability.
- Check for firmware updates periodically at Belkin’s official support portal, in case a patch is silently released in response to public pressure.
FAQ
Q1: Can this vulnerability be exploited without any authentication?
No CVE-2026-5608 requires low-privilege authentication (CVSS PR:L), meaning the attacker must possess at least a basic valid credential for the router’s web interface.
However, this should not be mistaken for meaningful protection. The vast majority of consumer routers are shipped with factory-default credentials that are never changed, making this prerequisite trivially satisfied in real-world attack scenarios. Enforcing strong, unique passwords significantly reduces the risk of exploitation.
Q2: Is there an official patch available for CVE-2026-5608?
As of April 6, 2026, no official patch or security advisory has been released by Belkin. The vendor did not respond to the researcher’s prior disclosure notification.
Users of the Belkin F9K1122 running firmware 1.00.33 should apply the recommended mitigations above and monitor Belkin’s support channels for any future firmware updates. Given the device’s legacy status, an official fix may not be forthcoming, making device replacement the most reliable long-term remediation.
Site: thecybrdef.com
Reference:
| https://github.com/Litengzheng/vul_db/blob/main/Belkin/vul_80/README.md |
| https://vuldb.com/vuln/355399/cti |
| https://vuldb.com/submit/785315 |
| https://vuldb.com/vuln/355399 |
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