CVE-2026-36796 Overview
CVE-2026-36796 is a stack overflow vulnerability in Shenzhen Tenda Technology Co., Ltd Tenda G0 firmware version v15.11.0.5. The flaw resides in the formCropAndSetWewifiPic function, where the picCropName parameter is processed without proper bounds checking. A remote attacker can send a crafted HTTP request to trigger the overflow and cause a Denial of Service (DoS) condition on the affected device. The vulnerability is classified under CWE-120 (Buffer Copy without Checking Size of Input). No authentication or user interaction is required to exploit this issue, making the attack surface accessible to any network-adjacent adversary capable of reaching the device's web management interface.
Critical Impact
Unauthenticated remote attackers can crash the Tenda G0 router by sending a single crafted HTTP request, disrupting network availability for all connected clients.
Affected Products
- Shenzhen Tenda Technology Co., Ltd Tenda G0
- Tenda G0 firmware version v15.11.0.5
- Web management interface exposing the formCropAndSetWewifiPic endpoint
Discovery Timeline
- 2026-06-09 - CVE-2026-36796 published to NVD
- 2026-06-10 - Last updated in NVD database
Technical Details for CVE-2026-36796
Vulnerability Analysis
The vulnerability exists in the formCropAndSetWewifiPic function, which handles HTTP requests related to WiFi picture cropping operations on the Tenda G0 router. The function reads the picCropName parameter from the incoming HTTP request and copies its contents into a fixed-size stack buffer without validating the input length. When an attacker supplies a picCropName value that exceeds the destination buffer size, adjacent stack memory is overwritten, corrupting saved registers and the return address. The result is a process crash that terminates the web service and disrupts router functionality.
The issue is consistent with a classic stack-based buffer overflow pattern frequently observed in embedded MIPS and ARM router firmware. While the CVSS impact metrics indicate availability impact only, stack corruption in embedded targets can sometimes be escalated to code execution depending on memory protections in the firmware build.
Root Cause
The root cause is missing input length validation on the picCropName HTTP parameter before it is copied into a stack-allocated buffer. The function relies on unsafe string copy semantics rather than bounded copy primitives. No size check is performed against the destination buffer length.
Attack Vector
An unauthenticated attacker on the same network as the device sends an HTTP request to the vulnerable endpoint with an oversized picCropName value. The request triggers the stack overflow inside formCropAndSetWewifiPic, crashing the web management process. Proof-of-concept material is referenced in the GitHub PoC Repository. The EPSS score for this vulnerability is reported as 0.254%.
// Synthetic code not provided - see referenced PoC repository
// for technical details on the request structure and overflow trigger.
Detection Methods for CVE-2026-36796
Indicators of Compromise
- Unexpected reboots or crashes of the Tenda G0 router, particularly of the web management daemon.
- HTTP POST requests to endpoints invoking formCropAndSetWewifiPic containing abnormally long picCropName parameter values.
- Loss of network connectivity for clients behind the affected device coinciding with inbound HTTP traffic to the management interface.
Detection Strategies
- Inspect HTTP traffic to the router management interface for requests containing picCropName parameter values exceeding typical filename lengths (for example, more than 128 bytes).
- Deploy network IDS/IPS signatures that flag oversized parameter values targeting Tenda form* endpoints.
- Correlate router availability monitoring alerts with HTTP request logs from upstream proxies or perimeter devices.
Monitoring Recommendations
- Monitor management plane traffic and restrict access to trusted administrative subnets only.
- Log and alert on repeated HTTP requests to formCropAndSetWewifiPic from a single source.
- Track router uptime metrics via SNMP or syslog to identify abnormal restart patterns indicative of crash-and-reboot cycles.
How to Mitigate CVE-2026-36796
Immediate Actions Required
- Restrict access to the Tenda G0 web management interface to trusted internal networks only. Block external exposure on WAN interfaces.
- Disable remote management features if they are not strictly required for operations.
- Place vulnerable devices behind a network firewall that filters unsolicited HTTP requests to the management port.
Patch Information
No vendor advisory or firmware patch is referenced in the NVD entry for CVE-2026-36796 at the time of publication. Affected operators should monitor the Tenda official support site for firmware updates addressing the formCropAndSetWewifiPic function. Until a patched firmware is released, operators must rely on compensating network controls.
Workarounds
- Segment the router management interface onto a dedicated VLAN accessible only to administrative hosts.
- Apply ACLs at upstream switches or firewalls to drop HTTP traffic to the router management port from untrusted sources.
- Replace end-of-life or unsupported Tenda G0 devices with currently maintained hardware where firmware updates are unavailable.
# Example: restrict access to router management interface using iptables
# Replace 192.168.1.1 with the router IP and 10.0.0.0/24 with the admin subnet
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -s 10.0.0.0/24 -j ACCEPT
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
