CVE-2025-7854 Overview
CVE-2025-7854 is a stack-based buffer overflow in the Tenda FH451 router running firmware version 1.0.0.9. The flaw resides in the fromVirtualSer function handling requests to /goform/VirtualSer. Attackers manipulate the page argument to overflow a fixed-size stack buffer. The vulnerability is exploitable over the network and has been publicly disclosed, including proof-of-concept details on GitHub and VulDB.
Critical Impact
Remote attackers with low privileges can corrupt stack memory in the FH451 web management interface, leading to denial of service or potential arbitrary code execution on the device.
Affected Products
- Tenda FH451 router (hardware)
- Tenda FH451 firmware version 1.0.0.9
- Web management interface endpoint /goform/VirtualSer
Discovery Timeline
- 2025-07-19 - CVE-2025-7854 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-7854
Vulnerability Analysis
The vulnerability lives in the fromVirtualSer handler within the Tenda FH451 HTTP management daemon. The handler processes the page parameter submitted to /goform/VirtualSer without enforcing length validation before copying it into a fixed-size stack buffer. An attacker who can reach the web interface and authenticate with low privileges can submit an oversized page value to corrupt adjacent stack memory, including saved return addresses. CWE-119 classifies this as improper restriction of operations within the bounds of a memory buffer. Public proof-of-concept material is available, increasing the likelihood of opportunistic exploitation against exposed devices.
Root Cause
The fromVirtualSer function copies the attacker-controlled page query parameter into a stack-allocated buffer using an unbounded string operation. No length check is performed against the destination buffer size, allowing overflow into the saved frame pointer and return address. This pattern is recurrent across Tenda /goform/* endpoints, which historically rely on direct strcpy-style operations against CGI-style request parameters.
Attack Vector
Exploitation requires network access to the device's web management interface and a low-privilege session. The attacker sends a crafted HTTP request to /goform/VirtualSer with an oversized page argument. Successful exploitation can trigger a crash of the management daemon, resulting in denial of service, or in a controlled overflow scenario can redirect execution to attacker-supplied shellcode running with the privileges of the HTTP service. The vulnerability is remotely reachable and does not require user interaction.
The vulnerability manifests as an unchecked copy of the page request parameter into a fixed-size stack buffer within the fromVirtualSer routine. See the GitHub Vulnerability Report and VulDB #316944 Detailed Info for technical analysis and PoC details.
Detection Methods for CVE-2025-7854
Indicators of Compromise
- HTTP POST or GET requests to /goform/VirtualSer containing an unusually long page parameter value.
- Unexpected restarts or crashes of the Tenda FH451 web management service, especially after external requests.
- Repeated connection attempts to the router's HTTP management port from untrusted source addresses.
Detection Strategies
- Inspect web server and router syslog output for malformed requests targeting /goform/VirtualSer endpoints.
- Deploy network IDS signatures that flag HTTP requests with page parameter lengths exceeding expected bounds (typically > 256 bytes).
- Correlate management interface crashes with inbound request patterns to identify probing or exploitation attempts.
Monitoring Recommendations
- Monitor traffic volume and HTTP request anomalies to the router's management interface from both LAN and WAN sources.
- Alert on any access to /goform/VirtualSer originating from external IP ranges if remote management is not in use.
- Capture and review full HTTP request bodies in environments where this device is in scope for compliance monitoring.
How to Mitigate CVE-2025-7854
Immediate Actions Required
- Disable remote (WAN-side) administration on the Tenda FH451 until a vendor patch is available.
- Restrict LAN-side access to the web management interface to a dedicated management VLAN or trusted host list.
- Rotate administrative credentials to limit reuse if low-privilege accounts have been shared or exposed.
- Place the device behind a network firewall or ACL that blocks unsolicited inbound HTTP traffic to the router.
Patch Information
No vendor-supplied patch or security advisory from Tenda is referenced in the public CVE record at the time of writing. Operators should monitor the Tenda Official Website for firmware updates addressing the fromVirtualSer function and consider replacement of end-of-life FH451 hardware if no fix is released.
Workarounds
- Block external access to TCP ports 80 and 443 on the router's WAN interface using upstream filtering.
- Segment the FH451 onto an isolated management network where only authorized administrators can reach /goform/* endpoints.
- Where feasible, replace the FH451 with a currently supported device that receives active security maintenance.
# Example: block external access to the router's HTTP management interface
iptables -A INPUT -i wan0 -p tcp --dport 80 -j DROP
iptables -A INPUT -i wan0 -p tcp --dport 443 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
