Tenda W20E
CVE-2026-36820
HIGH
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessIdentify Tenda W20E httpd on LAN or exposed WAN
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DeliveryCraft oversized webAuthWhiteUserInfo POST body
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ExploitSend HTTP request to formAddWebAuthWhiteUser endpoint
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ExecutionOverflow stack buffer in httpd handler
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PersistCorrupt saved return address, crash process
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ImpactRouter management plane and routing unavailable until power cycle
Vulnerability Assessment
| Weakness |
CWE
ASVS 5.0
V15 - Secure Coding and Architecture Stack buffer bounds checking
MITRE ATT&CK
1 technique across 1 tactic: Execution The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Exploitation Conditions | Attacker must be able to reach the Tenda W20E HTTP management interface and POST to the formAddWebAuthWhiteUser handler with a crafted webAuthWhiteUserInfo parameter exceeding the expected length on firmware v15.11.0.6. Per CVSS PR:N/UI:N, no authentication or user interaction is required, but the management interface is by default LAN-only on Tenda SOHO/SMB routers, so exploitation realistically requires either LAN access (wired, Wi-Fi, or via a foothold on an internal host) or that the administrator has explicitly enabled WAN-side remote management. Limiting factors: only firmware build 15.11.0.6 is named in the CVE (other versions unverified), impact is currently demonstrated only as DoS rather than code execution, and the device must be running the captive-portal/web-auth feature path for the vulnerable handler to be registered. |
| Impact | Signals are mixed and warrant careful interpretation. CVSS 7.5 with vector AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H indicates a network-reachable, low-complexity, unauthenticated attack with high availability impact only - a classic remote DoS profile rather than RCE. EPSS and CISA KEV data were not provided in the input, so exploitation probability and active-exploitation status are unknown; no public exploit identified at time of analysis, though the referenced GitHub repository (SemVulLLM) suggests an LLM-assisted vulnerability dataset that may contain trigger details. A critical scoping caveat: 'network' in CVSS for a SOHO/enterprise router web UI usually means LAN-adjacent rather than Internet-reachable, unless WAN-side remote management is enabled - this materially lowers real-world risk versus the raw 7.5 score. Buffer overflows in CWE-121 contexts also sometimes turn out to be exploitable for code execution beyond DoS, so the C:N/I:N rating should be treated as the currently demonstrated impact, not a proven upper bound. |
| Exploit ScenarioDerived | An attacker with LAN connectivity (for example, a guest Wi-Fi client, a compromised internal host, or any Internet host if remote management is exposed) sends a single crafted HTTP POST to the formAddWebAuthWhiteUser endpoint with an oversized webAuthWhiteUserInfo parameter. The router's httpd process crashes due to stack corruption, taking down the management plane and frequently network connectivity, requiring a manual power cycle. Because the CVSS vector is AC:L/PR:N/UI:N, the attack is one-shot and scriptable, and could be repeated to keep the device unavailable. |
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Alert meAnalysisAIv1 – Jun 09, 2026
Denial of service in Tenda W20E router firmware v15.11.0.6 allows remote unauthenticated attackers to crash the device by sending a crafted HTTP request that triggers a stack-based buffer overflow in the webAuthWhiteUserInfo parameter of the formAddWebAuthWhiteUser function. No public exploit identified at time of analysis, though a research repository documenting the flaw is referenced. The CVSS 7.5 (High) score reflects pure availability impact with no confidentiality or integrity loss.
RemediationAI
No vendor-released patch identified at time of analysis - no Tenda security advisory or fixed firmware version is referenced in the available data, so users should monitor https://www.tendacn.com for a W20E firmware update superseding 15.11.0.6 and apply it once available. As compensating controls, disable remote (WAN-side) HTTP/HTTPS management entirely to remove Internet exposure (side effect: administrators must be on the LAN or VPN to manage the device), restrict access to the management interface to a dedicated admin VLAN or specific source IPs via ACL (side effect: breaks ad-hoc support workflows), and place the device behind an upstream firewall or IPS with rules that drop oversized or malformed POST bodies to /goform/formAddWebAuthWhiteUser. For high-availability environments, treat the W20E as end-of-support if Tenda does not respond and plan migration to a vendor with an active PSIRT process; the referenced research artifact at https://github.com/xhh0124/SemVulLLM/tree/main/W20E/formAddWebAuthWhiteUser can inform detection signatures.
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Technical ContextAI · show details
The Tenda W20E is an enterprise-grade wireless router whose web management interface exposes a CGI-style handler named formAddWebAuthWhiteUser, used to add users to the captive-portal/web-authentication whitelist. The flaw is classified as CWE-121 (Stack-Based Buffer Overflow), meaning a fixed-size stack buffer is populated from the webAuthWhiteUserInfo HTTP parameter without proper length validation. On embedded MIPS/ARM Tenda firmware lineage, this handler is implemented in the httpd binary and is reachable through the LAN-side management HTTP server, where overflowing the stack frame corrupts the saved return address and crashes the web/management daemon, breaking router administration and frequently the routing data plane that shares the process tree.
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Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Primary rating from Vendor (mitre) · only source for this CVE.
CVSS VectorVendor: mitre
Lifecycle Timeline
2DescriptionCVE.org
Shenzhen Tenda Technology Co., Ltd Tenda W20E v15.11.0.6 was discovered to contain a buffer overflow in the webAuthWhiteUserInfo parameter of the formAddWebAuthWhiteUser function. This vulnerability allows attackers to cause a Denial of Service (DoS) via a crafted HTTP request.
Executive ViewAI
Tenda W20E routers running firmware v15.11.0.6 are vulnerable to remote denial-of-service attacks that can crash the device without user authentication, creating immediate risk of network outages across affected infrastructure. Since no vendor patch is available, organizations must implement interim controls or initiate hardware replacement to prevent potential business disruption.
No vendor-released patch identified at time of analysis. Interim mitigations: (1) Implement firewall rules and network segmentation to restrict external HTTP access to vulnerable routers; (2) Deploy rate limiting on inbound HTTP requests to the device; (3) Monitor network telemetry for anomalous HTTP traffic targeting the webAuthWhiteUserInfo parameter; (4) Evaluate hardware replacement timeline as primary remediation strategy.
Threat Intelligence Overview
NVD
CVE.org
EPSS
Vulnrichment
GitHub
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
A buffer overflow occurs when a program writes more data to a memory buffer than it was allocated to hold, causing the excess data to spill into adjacent memory regions.
A stack-based buffer overflow occurs when a program writes more data to a buffer located on the stack than it was allocated to hold.
Denial of Service attacks render applications or systems unavailable by overwhelming resources or triggering failure conditions.
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