CVE-2025-7796 Overview
CVE-2025-7796 is a stack-based buffer overflow vulnerability in the Tenda FH451 router firmware version 1.0.0.9. The flaw resides in the fromPptpUserAdd function within the /goform/PPTPDClient endpoint. Attackers can trigger memory corruption by supplying an oversized Username argument to the affected handler. The vulnerability is exploitable remotely over the network and requires only low-level privileges. Public disclosure of the issue, including proof-of-concept material, has occurred through third-party vulnerability tracking sources.
Critical Impact
Remote attackers can corrupt the stack of the router's web management process, enabling arbitrary code execution and full compromise of the affected Tenda FH451 device.
Affected Products
- Tenda FH451 router (hardware)
- Tenda FH451 firmware version 1.0.0.9
- Web management interface endpoint /goform/PPTPDClient
Discovery Timeline
- 2025-07-18 - CVE-2025-7796 published to NVD
- 2025-07-23 - Last updated in NVD database
Technical Details for CVE-2025-7796
Vulnerability Analysis
The vulnerability lives in the fromPptpUserAdd function, which handles requests sent to the /goform/PPTPDClient web management endpoint on the Tenda FH451 router. This handler processes PPTP user account additions submitted from the administrative interface. The function copies the attacker-controlled Username parameter into a fixed-size stack buffer without enforcing a proper length check. Supplying a long Username value overflows the buffer and overwrites adjacent stack memory, including saved return addresses. The flaw is classified under [CWE-119] for improper restriction of operations within the bounds of a memory buffer.
Root Cause
The root cause is the absence of bounds validation on the Username HTTP parameter before it is written to a stack-allocated buffer inside fromPptpUserAdd. Embedded MIPS-based Tenda firmware commonly uses unsafe string routines such as strcpy or sprintf for request parsing. Without explicit length checks, any input longer than the destination buffer corrupts the stack frame of the request handler.
Attack Vector
An authenticated attacker with access to the router's web interface can issue a crafted HTTP POST request to /goform/PPTPDClient containing an oversized Username field. Because the management interface is reachable over the local network, and in some deployments over the WAN, exploitation does not require physical access. Successful exploitation can crash the httpd process, causing denial of service, or be developed into arbitrary code execution on the device. Technical analysis and proof-of-concept details are available in the GitHub vulnerability documentation and the VulDB entry.
Detection Methods for CVE-2025-7796
Indicators of Compromise
- HTTP POST requests to /goform/PPTPDClient containing abnormally long Username values, typically exceeding several hundred bytes.
- Unexpected restarts, crashes, or unresponsiveness of the router's web management httpd process.
- New or unauthorized PPTP user accounts appearing in router configuration backups.
- Outbound connections from the router to unfamiliar hosts following suspicious management requests.
Detection Strategies
- Inspect HTTP traffic destined for the Tenda management interface and alert on Username parameters exceeding expected length limits.
- Deploy network IDS signatures that flag requests to /goform/PPTPDClient with non-printable bytes or shellcode patterns in form fields.
- Correlate router syslog events showing httpd crashes with preceding HTTP POST requests for forensic timeline reconstruction.
Monitoring Recommendations
- Forward router syslog and crash events to a centralized logging platform for retention and analysis.
- Monitor administrative access to the FH451 web interface and restrict it to known management subnets.
- Track firmware version 1.0.0.9 across inventory and prioritize replacement or isolation of affected devices.
How to Mitigate CVE-2025-7796
Immediate Actions Required
- Disable WAN-side access to the Tenda FH451 web management interface and limit LAN access to trusted administrative hosts.
- Disable the PPTP server feature if it is not required, removing the attack surface exposed by /goform/PPTPDClient.
- Rotate administrative credentials on the device to limit the value of any low-privilege account an attacker might obtain.
- Place vulnerable FH451 devices behind a segmentation boundary that blocks untrusted hosts from reaching management endpoints.
Patch Information
No vendor patch is referenced in the available advisory data for CVE-2025-7796. The Tenda official website should be checked for firmware updates that supersede version 1.0.0.9. Until a fixed firmware is published, organizations should treat the FH451 as end-of-support for production workloads and plan replacement with a supported device.
Workarounds
- Restrict management interface access using an upstream firewall ACL that permits only specific administrator IP addresses.
- Disable the PPTP service in the router configuration to eliminate the vulnerable code path.
- Place the router behind a reverse proxy or VPN concentrator that authenticates and filters administrative traffic before it reaches /goform/PPTPDClient.
# Configuration example: block external access to the Tenda web interface
# Apply on an upstream firewall in front of the FH451
iptables -A FORWARD -p tcp --dport 80 -d <FH451_IP> -s <ADMIN_SUBNET> -j ACCEPT
iptables -A FORWARD -p tcp --dport 443 -d <FH451_IP> -s <ADMIN_SUBNET> -j ACCEPT
iptables -A FORWARD -p tcp --dport 80 -d <FH451_IP> -j DROP
iptables -A FORWARD -p tcp --dport 443 -d <FH451_IP> -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
