CVE-2026-36822 Overview
CVE-2026-36822 is a stack-based buffer overflow [CWE-121] in Shenzhen Tenda Technology Co., Ltd Tenda W20E router firmware version v15.11.0.6. The flaw resides in the formDelStaState function, which fails to validate the length of the macAddr parameter supplied through HTTP requests. Remote, unauthenticated attackers can submit a crafted HTTP request to trigger memory corruption and cause a Denial of Service (DoS) condition on the affected device. The vulnerability requires no privileges and no user interaction, making it reachable across any network path that exposes the router's web management interface.
Critical Impact
Unauthenticated attackers can remotely crash the Tenda W20E router, disrupting network availability for all connected clients.
Affected Products
- Shenzhen Tenda Technology Co., Ltd Tenda W20E
- Firmware version v15.11.0.6
- Devices exposing the HTTP management interface
Discovery Timeline
- 2026-06-09 - CVE-2026-36822 published to NVD
- 2026-06-09 - Last updated in NVD database
Technical Details for CVE-2026-36822
Vulnerability Analysis
The vulnerability is a stack-based buffer overflow [CWE-121] within the formDelStaState handler of the Tenda W20E web management application. The handler processes HTTP requests intended to remove a station's state entry and reads the macAddr parameter from the request body. The function copies the attacker-controlled macAddr value into a fixed-size stack buffer without enforcing a length check. An oversized value overwrites adjacent stack memory, including saved return addresses and frame pointers, corrupting the execution state of the web service process.
Because the affected process runs as part of the router's core management daemon, corruption leads to a process crash and loss of management and routing functions. The CWE-121 classification and the EPSS score of 0.254% indicate that exploitation is straightforward but not yet widely observed in active campaigns.
Root Cause
The root cause is missing input validation on the macAddr parameter. The formDelStaState function does not verify that the supplied MAC address conforms to a fixed length or expected format before copying it into a stack buffer. Standard unsafe string handling on embedded MIPS or ARM platforms compounds the issue by performing the copy without bounds checking.
Attack Vector
Exploitation requires only network access to the router's HTTP management interface. An attacker sends a crafted HTTP POST request to the endpoint that invokes formDelStaState, supplying an overlong macAddr value. The request triggers the overflow, corrupts the stack, and crashes the web service. Successful exploitation produces an availability impact, disrupting routing, DHCP, and management for all downstream clients until the device restarts.
No verified exploit code is published in the NVD record. A proof-of-concept reference is hosted in the GitHub PoC Repository.
Detection Methods for CVE-2026-36822
Indicators of Compromise
- HTTP POST requests targeting the formDelStaState endpoint with abnormally long macAddr parameter values.
- Unexpected reboots or crashes of the Tenda W20E web management service, often correlating with loss of LAN connectivity.
- Repeated inbound HTTP traffic to the router management interface from untrusted sources.
Detection Strategies
- Inspect HTTP request bodies destined for the router management interface and flag macAddr values that exceed standard MAC address length (17 characters).
- Correlate router availability monitoring data with web service crash events to identify exploitation attempts.
- Apply network intrusion detection signatures that match oversized form parameters posted to Tenda management endpoints.
Monitoring Recommendations
- Collect syslog and SNMP traps from the Tenda W20E device and forward them to a centralized logging platform for analysis.
- Track repeated TCP resets or service restarts on the router's HTTP management port as a sign of crash exploitation.
- Alert on any inbound HTTP traffic to the router management interface originating from outside trusted administrative networks.
How to Mitigate CVE-2026-36822
Immediate Actions Required
- Restrict access to the Tenda W20E web management interface to trusted administrative hosts using firewall ACLs.
- Disable remote (WAN-side) management on affected devices until a vendor patch is applied.
- Place affected routers behind a perimeter device that can filter malformed HTTP requests to the management interface.
Patch Information
No vendor advisory or firmware patch is referenced in the NVD record at the time of publication. Monitor the Tenda support portal and the GitHub PoC Repository for updated firmware releases addressing the formDelStaState flaw. Apply firmware updates as soon as they are released by Shenzhen Tenda Technology Co., Ltd.
Workarounds
- Segment the router management VLAN from user networks to reduce the attack surface for the HTTP management interface.
- Replace end-of-life or unpatched Tenda W20E devices with hardware that receives current security updates.
- Deploy an upstream web application firewall to drop HTTP requests containing oversized macAddr parameters.
# Example iptables rule to restrict router management access to a trusted host
iptables -A INPUT -p tcp --dport 80 -s 192.0.2.10 -j ACCEPT
iptables -A INPUT -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.
