CVE-2026-67822 Overview
CVE-2026-67822 is a stack-based buffer overflow vulnerability affecting the Tenda W6-S wireless router, firmware version 1.0.0.4(510). The flaw resides in the formwrlSSIDset function, which handles requests to the /goform/wifiSSIDset endpoint. The function uses sprintf to concatenate the attacker-controlled GO and index parameters into a fixed 64-byte stack buffer without any length validation. An unauthenticated remote attacker can send a crafted HTTP request to corrupt the stack and potentially achieve arbitrary code execution on the device.
Critical Impact
Unauthenticated network attackers can trigger a stack overflow in the router's web management interface, enabling denial of service or remote code execution with full device compromise.
Affected Products
- Tenda W6-S wireless router
- Firmware version 1.0.0.4(510)
- /goform/wifiSSIDset web management endpoint
Discovery Timeline
- 2026-07-31 - CVE-2026-67822 published to the National Vulnerability Database (NVD)
- 2026-07-31 - Last updated in NVD database
Technical Details for CVE-2026-67822
Vulnerability Analysis
The vulnerability is classified as a stack-based buffer overflow [CWE-121]. The affected code path lives in the formwrlSSIDset handler, which processes HTTP POST requests to /goform/wifiSSIDset. This endpoint is exposed by the router's embedded HTTP server for wireless SSID configuration.
The handler retrieves two request parameters, GO and index, directly from the attacker's HTTP request. It then passes both values to sprintf and writes the formatted result into a 64-byte stack-allocated buffer. Because sprintf performs no bounds checking, oversized GO or index values overflow the destination buffer and overwrite adjacent stack memory, including the saved return address.
Root Cause
The root cause is the unsafe use of sprintf with unvalidated, attacker-controlled input written into a fixed-size stack buffer. Safer alternatives such as snprintf with an explicit size limit, or explicit length checks on the GO and index parameters prior to formatting, would prevent the overflow. The parameters lack both length validation and character filtering before being consumed by the format function.
Attack Vector
Exploitation requires only network access to the router's HTTP management interface. No authentication or user interaction is needed. An attacker sends a crafted HTTP request to /goform/wifiSSIDset containing an oversized GO or index parameter. The resulting stack corruption can crash the device, causing denial of service, or hijack control flow to execute arbitrary code in the context of the router's HTTP daemon, typically running with elevated privileges on embedded Linux firmware.
The vulnerability mechanism is documented in the public proof-of-concept writeup. See the GitHub PoC Repository for technical details on the vulnerable code path and request structure.
Detection Methods for CVE-2026-67822
Indicators of Compromise
- HTTP POST requests to /goform/wifiSSIDset containing abnormally long GO or index parameter values exceeding 64 bytes.
- Unexpected reboots, crashes, or restarts of the router's HTTP management daemon.
- Unusual outbound traffic from the router following a suspicious inbound HTTP request, indicating possible post-exploitation activity.
Detection Strategies
- Deploy network intrusion detection signatures that inspect HTTP request bodies to /goform/wifiSSIDset and alert on parameter values exceeding safe length thresholds.
- Correlate router syslog events reporting HTTP daemon crashes with preceding inbound requests to the wifiSSIDset endpoint.
- Monitor for repeated requests to /goform/ administrative endpoints originating from untrusted network segments.
Monitoring Recommendations
- Forward router management-plane logs to a centralized log analytics platform for anomaly detection.
- Baseline normal administrative traffic to /goform/* endpoints and alert on deviations in request size or frequency.
- Track device availability and unexpected configuration changes to the wireless SSID as potential exploitation indicators.
How to Mitigate CVE-2026-67822
Immediate Actions Required
- Restrict access to the router's web management interface to trusted LAN segments only, and disable WAN-side administration.
- Place the device behind a network firewall that blocks unsolicited inbound HTTP requests to the router.
- Segment vulnerable Tenda W6-S devices away from sensitive assets pending a vendor firmware update.
Patch Information
At the time of publication, no vendor advisory or patched firmware has been published for CVE-2026-67822. Monitor Tenda's official support channels for a firmware release addressing the formwrlSSIDset handler in versions succeeding 1.0.0.4(510).
Workarounds
- Disable remote (WAN-side) HTTP management on the router configuration page.
- Enforce ACLs on upstream network devices to permit management access only from designated administrative hosts.
- Change default administrative credentials and use a strong password to raise the bar against chained attacks, even though this vulnerability is pre-authentication.
- Consider replacing the affected model with a supported device if a vendor patch is not released in a reasonable timeframe.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
