CVE-2026-9428: Tenda F1202 Buffer Overflow Vulnerability

CVE-2026-9428 Overview

CVE-2026-9428 is a stack-based buffer overflow vulnerability in the Tenda F1202 router running firmware version 1.2.0.20(408). The flaw resides in the fromPPTPUserSetting function handling requests to the /goform/PPTPUserSetting endpoint. Attackers can trigger memory corruption by manipulating the delno argument, leading to control over the program's execution flow. The vulnerability is exploitable over the network and a public proof-of-concept has been disclosed, increasing the risk of opportunistic attacks against exposed devices.

Critical Impact

Remote attackers with low privileges can corrupt stack memory on affected Tenda F1202 devices, potentially achieving arbitrary code execution and full device compromise.

Affected Products

• Tenda F1202 router, firmware version 1.2.0.20(408)
• Web management interface endpoint /goform/PPTPUserSetting
• fromPPTPUserSetting function processing the delno parameter

Discovery Timeline

• 2026-05-25 - CVE-2026-9428 published to the National Vulnerability Database (NVD)
• 2026-05-26 - Last updated in NVD database

Technical Details for CVE-2026-9428

Vulnerability Analysis

The vulnerability is classified as a stack-based buffer overflow under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer). It affects the PPTP user configuration handler exposed through the device's web management interface. Attackers send a crafted HTTP request to /goform/PPTPUserSetting containing an oversized or malformed delno value. The fromPPTPUserSetting function copies attacker-supplied data into a fixed-size stack buffer without proper length validation. This overflow overwrites adjacent stack memory, including saved return addresses and function pointers used by the embedded web server.

Root Cause

The root cause is missing bounds checking on the delno argument before it is written into a stack-allocated buffer. Embedded SOHO router firmware frequently relies on unsafe C string operations such as strcpy or sprintf when parsing CGI parameters. Without input length validation, attacker-controlled data extends beyond the buffer boundary and corrupts adjacent stack frames.

Attack Vector

The attack is performed remotely over the network against the device's HTTP management service. An authenticated user with low privileges can submit a malicious POST request to the /goform/PPTPUserSetting endpoint with a crafted delno parameter. Successful exploitation can crash the device, cause denial of service, or hijack execution. A public proof-of-concept is referenced in the GitHub PoC Repository and VulDB #365409.

No verified exploit code is included here. Refer to the published PoC for technical reproduction details.

Detection Methods for CVE-2026-9428

Indicators of Compromise

• Unexpected HTTP POST requests to /goform/PPTPUserSetting containing unusually long delno parameter values
• Repeated reboots, crashes, or unresponsiveness of the Tenda F1202 web management interface
• Outbound connections from the router to unfamiliar IP addresses following PPTP configuration requests
• Unauthorized changes to PPTP user entries or router configuration

Detection Strategies

• Inspect HTTP request bodies destined for /goform/PPTPUserSetting and flag oversized delno parameters that exceed expected lengths
• Monitor the router's syslog or remote logging stream for segmentation faults and httpd restarts correlated with management interface traffic
• Apply network IDS signatures that detect anomalous binary or padded payloads sent to embedded device CGI endpoints

Monitoring Recommendations

• Restrict and log all access to router management interfaces, particularly from untrusted network segments
• Baseline normal administrative traffic patterns and alert on deviations targeting PPTP configuration endpoints
• Forward network telemetry from the gateway segment to a centralized analytics platform for correlation with broader threat activity

How to Mitigate CVE-2026-9428

Immediate Actions Required

• Disable remote (WAN-side) administration on affected Tenda F1202 devices until a vendor patch is verified and applied
• Restrict LAN access to the web management interface to a dedicated administrative VLAN or trusted hosts only
• Rotate administrative credentials and audit existing PPTP user entries for unauthorized modifications
• Monitor the Tenda official website for firmware updates addressing this vulnerability

Patch Information

At the time of publication, no vendor-supplied patch has been confirmed in the NVD record. Users should consult Tenda's support channels directly and apply firmware updates as soon as they are released. Until a patch is available, network-level compensating controls are required.

Workarounds

• Place affected routers behind an upstream firewall and block external access to TCP ports used by the web management service
• Disable the PPTP server feature if it is not in active use to reduce exposure of the vulnerable endpoint
• Segment IoT and SOHO network equipment away from production assets to limit lateral movement following compromise
• Replace end-of-life or unpatched devices with supported hardware where vendor updates are unavailable

# Configuration example: block external access to the router management interface
iptables -A INPUT -i wan0 -p tcp --dport 80 -j DROP
iptables -A INPUT -i wan0 -p tcp --dport 443 -j DROP
iptables -A INPUT -i wan0 -p tcp --dport 8080 -j DROP