CVE-2026-6199 Overview
CVE-2026-6199 is a stack-based buffer overflow vulnerability affecting Tenda F456 firmware version 1.0.0.5. The flaw resides in the fromqossetting function within the /goform/qossetting endpoint. Attackers can trigger the overflow by manipulating the page argument in HTTP requests sent to the device. The vulnerability is remotely exploitable and a public exploit has been disclosed. The weakness is classified under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer).
Critical Impact
Remote attackers can corrupt stack memory on affected Tenda F456 routers, potentially leading to arbitrary code execution or denial of service against the device's web management interface.
Affected Products
- Tenda F456 router firmware version 1.0.0.5
- The /goform/qossetting HTTP endpoint
- The fromqossetting handler function
Discovery Timeline
- 2026-04-13 - CVE-2026-6199 published to NVD
- 2026-04-22 - Last updated in NVD database
Technical Details for CVE-2026-6199
Vulnerability Analysis
The vulnerability exists in the fromqossetting function used to process Quality of Service (QoS) configuration requests submitted to /goform/qossetting. The function copies the user-supplied page parameter into a fixed-size stack buffer without enforcing length validation. When the input exceeds the destination buffer, adjacent stack memory is overwritten, including saved registers and the return address.
This class of flaw is common in embedded MIPS/ARM router firmware where strcpy, sprintf, or memcpy operations process HTTP form parameters without bounds checks. Successful exploitation typically yields control of the program counter, allowing execution of injected shellcode or return-oriented programming (ROP) chains within the httpd process running as root on most consumer routers.
Root Cause
The root cause is improper restriction of operations within the bounds of a memory buffer [CWE-119]. The fromqossetting handler trusts the length of the attacker-controlled page argument and writes it into a stack-allocated buffer of fixed size. No length validation occurs prior to the copy operation.
Attack Vector
The vulnerability is reachable over the network through the router's web management interface. An attacker with access to the management interface and low-privileged credentials can submit a crafted POST request to /goform/qossetting containing an oversized page parameter. Because routers are frequently exposed to LAN clients and occasionally to WAN-facing management, the attack surface is broad. A public proof-of-concept exists, increasing the likelihood of opportunistic exploitation.
The vulnerability mechanism is described in the GitHub Vulnerability Repository and the VulDB #357121 advisory. No verified exploit code is reproduced here.
Detection Methods for CVE-2026-6199
Indicators of Compromise
- HTTP POST requests to /goform/qossetting containing unusually large page parameter values
- Unexpected reboots, watchdog resets, or crashes of the httpd process on Tenda F456 routers
- Outbound connections from the router to unfamiliar hosts following web interface activity
- New or modified firewall, DNS, or QoS configuration entries that were not made by an administrator
Detection Strategies
- Inspect web server and reverse proxy logs for requests targeting /goform/qossetting with oversized parameter lengths
- Deploy network IDS rules to alert on HTTP request bodies exceeding expected sizes for Tenda goform endpoints
- Baseline router management traffic and flag deviations such as repeated POST requests from a single internal host
Monitoring Recommendations
- Forward router syslog data to a centralized logging platform for retention and correlation
- Monitor DNS queries originating from router IP addresses for signs of post-exploitation command-and-control
- Track firmware version inventory across deployed Tenda devices to identify unpatched units
How to Mitigate CVE-2026-6199
Immediate Actions Required
- Restrict access to the Tenda F456 web management interface to trusted management VLANs only
- Disable WAN-side remote administration if it is currently enabled
- Change default and weak administrator credentials, since exploitation requires low-privileged authentication
- Place affected routers behind a network segmentation boundary until a vendor patch is verified
Patch Information
At the time of publication, no fixed firmware release has been identified in the available references. Consult the Tenda Official Website for firmware update notices specific to the F456 product line. Apply any official update that addresses the fromqossetting handler as soon as it becomes available.
Workarounds
- Block external access to /goform/qossetting at an upstream firewall or web application gateway
- Disable the QoS feature in the router configuration to reduce reachability of the vulnerable handler where feasible
- Replace end-of-life or unsupported Tenda F456 devices with a vendor-supported alternative if no patch is released
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
