CVE-2026-9430: Tenda F1202 Buffer Overflow Vulnerability

CVE-2026-9430 Overview

CVE-2026-9430 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 formGstDhcpSetSer function handling requests to the /goform/GstDhcpSetSerof endpoint. Attackers can manipulate the dips argument to overflow the fixed-size stack buffer. The vulnerability is exploitable remotely over the network, and a public proof-of-concept has been disclosed.

Critical Impact

Remote attackers with low-privilege access can corrupt stack memory on affected Tenda F1202 devices, potentially leading to denial of service or arbitrary code execution on the router.

Affected Products

• Tenda F1202 router, firmware 1.2.0.20(408)
• Web management interface endpoint /goform/GstDhcpSetSerof
• formGstDhcpSetSer request handler function

Discovery Timeline

• 2026-05-25 - CVE-2026-9430 published to NVD
• 2026-05-26 - Last updated in NVD database

Technical Details for CVE-2026-9430

Vulnerability Analysis

The vulnerability is classified under [CWE-119], improper restriction of operations within the bounds of a memory buffer. The formGstDhcpSetSer function processes guest network DHCP server configuration requests sent to /goform/GstDhcpSetSerof. The handler reads the dips parameter from the HTTP request body without validating its length before copying it into a fixed-size stack buffer.

When an attacker supplies a dips value exceeding the destination buffer size, adjacent stack memory is overwritten. This corruption can clobber saved return addresses and function pointers, redirecting control flow. On MIPS-based Tenda firmware, such conditions are commonly leveraged to achieve arbitrary code execution through return-oriented programming.

Root Cause

The root cause is the absence of bounds checking when handling the dips HTTP parameter inside formGstDhcpSetSer. The firmware uses unsafe string-copy semantics that trust attacker-controlled input length. Memory-corrupting primitives like strcpy or sprintf on stack buffers remain common in Tenda's goform web handlers.

Attack Vector

The attack vector is network-based and requires low privileges, typically authenticated access to the router's web management interface. An attacker sends a crafted HTTP POST request to /goform/GstDhcpSetSerof containing an oversized dips value. No user interaction is required. A public exploit is available in the referenced GitHub PoC Repository, increasing the likelihood of opportunistic exploitation against exposed devices.

For exploit specifics, consult the VulDB #365411 advisory rather than synthesized code.

Detection Methods for CVE-2026-9430

Indicators of Compromise

• HTTP POST requests targeting /goform/GstDhcpSetSerof containing abnormally long dips parameter values
• Unexpected reboots, watchdog resets, or httpd process crashes on Tenda F1202 devices
• Outbound connections from the router to unfamiliar hosts following suspicious management requests
• Unauthorized changes to guest DHCP server configuration in the device administration panel

Detection Strategies

• Inspect web traffic to the router for goform endpoint requests with parameters exceeding expected length thresholds
• Correlate management interface authentication events with subsequent crashes or service restarts on the router
• Monitor for known PoC signatures published in the GitHub PoC Repository

Monitoring Recommendations

• Forward router syslog and web server logs to a centralized log platform for retention and analysis
• Alert on repeated POST requests to /goform/GstDhcpSetSerof from a single source within short time windows
• Track failed login attempts to the Tenda management UI that precede malformed parameter submissions

How to Mitigate CVE-2026-9430

Immediate Actions Required

• Restrict access to the router's web management interface to trusted internal hosts only and disable remote WAN-side administration
• Change default and weak administrative credentials to reduce the chance an attacker reaches the authenticated endpoint
• Segment the Tenda F1202 from sensitive network zones until a vendor patch is verified
• Monitor the Tenda Official Website for firmware updates addressing CVE-2026-9430

Patch Information

As of the last NVD update on 2026-05-26, no vendor patch has been published for Tenda F1202 firmware 1.2.0.20(408). Administrators should track the VulDB #365411 entry and the Tenda Official Website for firmware advisories.

Workarounds

• Place the device behind a network firewall that blocks unsolicited inbound HTTP and HTTPS to the management interface
• Disable the guest network feature if it is not required, reducing exposure of the GstDhcpSetSerof handler
• Replace end-of-support or unpatched SOHO routers with actively maintained hardware where feasible

# Configuration example: restrict management interface access using an upstream firewall
# Allow only the administrative subnet to reach the router web UI
iptables -A FORWARD -s 10.0.0.0/24 -d 192.168.0.1 -p tcp --dport 80 -j ACCEPT
iptables -A FORWARD -d 192.168.0.1 -p tcp --dport 80 -j DROP
iptables -A FORWARD -d 192.168.0.1 -p tcp --dport 443 -j DROP