CVE-2026-36794 Overview
CVE-2026-36794 is a stack-based buffer overflow vulnerability affecting the Tenda W3 Wireless Router firmware version v1.0.0.3(2204). The flaw resides in the R7WebsSecurityHandler function, which processes authentication requests on the device's web management interface. Attackers can trigger multiple stack overflows by submitting crafted HTTP requests containing oversized username and password parameters. Successful exploitation causes the router to crash, resulting in a Denial of Service (DoS) condition. The vulnerability is exploitable remotely over the network without authentication or user interaction, classified under [CWE-121] Stack-based Buffer Overflow.
Critical Impact
Unauthenticated remote attackers can crash the Tenda W3 router by sending a single crafted HTTP request to the web management interface, disrupting wireless network connectivity.
Affected Products
- Shenzhen Tenda Technology Co., Ltd Tenda W3 Wireless Router
- Firmware version v1.0.0.3(2204)
- R7WebsSecurityHandler authentication component
Discovery Timeline
- 2026-06-09 - CVE-2026-36794 published to NVD
- 2026-06-10 - Last updated in NVD database
Technical Details for CVE-2026-36794
Vulnerability Analysis
The R7WebsSecurityHandler function in the Tenda W3 router's embedded web server handles security validation for incoming HTTP requests. The function processes the username and password parameters submitted by clients during authentication. The vulnerability stems from improper bounds checking when these parameter values are copied into fixed-size stack buffers.
When an attacker submits a crafted HTTP request containing overly long values for either parameter, the function writes beyond the allocated buffer boundaries on the stack. This corrupts adjacent stack memory, including saved return addresses and frame pointers. The resulting memory corruption causes the embedded web server process to crash, taking down the router's management interface and disrupting wireless services.
The issue affects multiple code paths within the same handler, indicating that both parameter processing routines share the same unsafe copy pattern.
Root Cause
The root cause is missing length validation on attacker-controlled HTTP parameters before copying them into stack-allocated buffers. The R7WebsSecurityHandler function uses unbounded string operations on user-supplied input, a pattern classified as [CWE-121] Stack-based Buffer Overflow. Embedded router firmware commonly exhibits this weakness due to reliance on C string functions without explicit length limits.
Attack Vector
The vulnerability is exploitable over the network with no authentication required. An attacker who can reach the router's web management interface, typically on the local network or via exposed remote administration, can send a single crafted HTTP POST request with oversized username or password field values. No user interaction is needed to trigger the crash.
The vulnerability mechanism is documented in the public proof-of-concept repository. See the GitHub PoC Repository for technical details on the parameter handling flaw.
Detection Methods for CVE-2026-36794
Indicators of Compromise
- Unexpected reboots or service restarts of the Tenda W3 router
- Web management interface becoming unresponsive after HTTP requests
- HTTP POST requests to authentication endpoints containing abnormally long username or password parameter values
- Loss of wireless connectivity correlated with inbound HTTP traffic to the router
Detection Strategies
- Inspect HTTP traffic destined for the router's management interface for requests with parameter lengths exceeding reasonable bounds (typically over 256 bytes for credential fields)
- Deploy network intrusion detection signatures that flag oversized authentication parameters targeting /goform/ endpoints common to Tenda devices
- Correlate router availability monitoring alerts with recent inbound HTTP requests to identify exploitation attempts
Monitoring Recommendations
- Enable logging on upstream firewalls for all traffic to the router's management port
- Monitor router uptime metrics via SNMP or ICMP to detect crash patterns indicating DoS attempts
- Alert on repeated HTTP requests to authentication endpoints from a single source within short time windows
How to Mitigate CVE-2026-36794
Immediate Actions Required
- Restrict access to the router's web management interface to trusted internal hosts only, blocking WAN-side administration
- Disable remote management features if not strictly required for operations
- Place vulnerable Tenda W3 devices behind a network firewall that filters HTTP traffic to management ports
- Monitor vendor channels for firmware updates addressing the R7WebsSecurityHandler flaw
Patch Information
No vendor patch has been published for CVE-2026-36794 at the time of NVD disclosure. Shenzhen Tenda Technology Co., Ltd has not issued a security advisory or firmware update for the Tenda W3 v1.0.0.3(2204) addressing this vulnerability. Organizations should track the vendor's support portal for firmware releases and apply updates as soon as they become available.
Workarounds
- Segment vulnerable routers onto isolated management VLANs accessible only to authorized administrators
- Apply access control lists (ACLs) on upstream switches to restrict HTTP traffic to the router's management interface
- Replace affected Tenda W3 devices with supported hardware if no firmware fix is forthcoming
- Disable the web management interface entirely and use alternative configuration methods where supported
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
