CVE-2025-7855: Tenda FH451 Buffer Overflow Vulnerability

CVE-2025-7855 Overview

CVE-2025-7855 is a stack-based buffer overflow in the Tenda FH451 router firmware version 1.0.0.9. The flaw resides in the fromqossetting function handling requests to /goform/qossetting. Manipulating the page argument triggers memory corruption on the stack. The attack can be launched remotely over the network and requires low-level privileges according to the published CVSS 4.0 vector. The vulnerability is tracked under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer). A public proof-of-concept is referenced in the GitHub PoC Repository, increasing the risk of opportunistic exploitation against exposed devices.

Critical Impact
Successful exploitation can corrupt the router's stack memory, enabling arbitrary code execution or full device compromise with impact on confidentiality, integrity, and availability.

Affected Products

Tenda FH451 router (hardware)
Tenda FH451 firmware version 1.0.0.9
Web management interface endpoint /goform/qossetting

Discovery Timeline

2025-07-19 - CVE-2025-7855 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-7855

Vulnerability Analysis

The vulnerability exists in the fromqossetting function exposed through the web management interface at /goform/qossetting. The handler processes the page HTTP parameter without enforcing length validation before copying it into a fixed-size stack buffer. An attacker who can reach the device's HTTP service and authenticate at a low privilege level can supply an oversized page value to overflow the stack frame. Overflowing the buffer overwrites adjacent stack data, including saved return addresses, allowing the attacker to redirect execution. Because the FH451 firmware runs without modern memory protections typical of embedded MIPS or ARM router targets, exploitation can lead to arbitrary code execution within the router's privileged context.

Root Cause

The root cause is the absence of bounds checking on user-supplied input before performing a memory copy into a stack-allocated buffer inside fromqossetting. The function trusts the size of the page parameter, violating [CWE-119] memory safety expectations. Embedded firmware of this class often relies on unsafe string handling routines such as strcpy or sprintf, which propagate attacker-controlled data directly into bounded buffers.

Attack Vector

Exploitation is performed remotely by sending a crafted HTTP POST request to /goform/qossetting with an oversized page argument. The attacker must reach the management interface, which on many SMB deployments is exposed on the LAN side and occasionally on the WAN side through misconfiguration. Once the stack is corrupted, the attacker can pivot to denial of service, persistent backdoor installation, or use the router as a foothold into adjacent network segments. Refer to the GitHub PoC Repository and VulDB entry #316945 for additional technical context.

Detection Methods for CVE-2025-7855

Indicators of Compromise

HTTP POST requests to /goform/qossetting containing abnormally long page parameter values, typically exceeding several hundred bytes.
Unexpected reboots, watchdog resets, or web service crashes on Tenda FH451 devices following inbound HTTP traffic.
Outbound connections from the router to unknown infrastructure following web management interface activity.
New or modified configuration entries on the device that do not match administrator change records.

Detection Strategies

Inspect web server and reverse proxy logs in front of the router for requests to /goform/qossetting with oversized parameters.
Deploy network intrusion detection signatures that flag HTTP requests targeting fromqossetting with page payloads beyond expected length.
Correlate device reboot events with preceding HTTP requests to identify exploitation attempts producing service crashes.

Monitoring Recommendations

Forward router syslog and HTTP access logs to a centralized SIEM for length-based anomaly analysis of management URIs.
Alert on any access to the FH451 web administration interface originating from untrusted network segments or external IP ranges.
Track device firmware versions across the fleet to identify hosts running the vulnerable 1.0.0.9 build.

How to Mitigate CVE-2025-7855

Immediate Actions Required

Restrict access to the FH451 web management interface to trusted management VLANs and block WAN-side exposure.
Disable remote management on the router until a vendor patch is applied.
Rotate administrative credentials and audit existing accounts on affected devices.
Inventory Tenda FH451 devices running firmware 1.0.0.9 and prioritize them for remediation.

Patch Information

No vendor security advisory or patched firmware release has been published at the time of writing. Monitor the Tenda Official Website for updated firmware addressing CVE-2025-7855. Until a fix is available, rely on network-level controls to reduce exposure.

Workarounds

Place the router behind a network firewall and permit HTTP/HTTPS access to the management interface only from designated administrative hosts.
Use ACLs on upstream switches to block traffic to /goform/qossetting from untrusted segments where feasible.
Consider replacing end-of-support or unpatched devices with hardware that receives active vendor security maintenance.

bash

# Configuration example: restrict management interface access with iptables on an upstream Linux gateway
iptables -A FORWARD -p tcp -d <ROUTER_IP> --dport 80 -s <ADMIN_SUBNET> -j ACCEPT
iptables -A FORWARD -p tcp -d <ROUTER_IP> --dport 80 -j DROP
iptables -A FORWARD -p tcp -d <ROUTER_IP> --dport 443 -s <ADMIN_SUBNET> -j ACCEPT
iptables -A FORWARD -p tcp -d <ROUTER_IP> --dport 443 -j DROP