# CVE-2026-36820: Tenda W20E buffer overflow in formAddWebAuthWhiteUser

Source: https://junglewise.ai/threats/cve-2026-36820-tenda-w20e-buffer-overflow-in-formaddwebauthwhiteuser  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-09. Updated: 2026-06-09  
License: CC BY 4.0 with a link back

CVE-2026-36820 · Severity: info · CVSS 7.5 · Published 2026-06-09

The Tenda W20E is a wireless router used for enterprise and small business networking. A security flaw in how the device handles web authentication settings allows an attacker to crash the router by sending a specially crafted web request. This results in a denial-of-service, cutting off internet access and network connectivity for all connected users until the device is recovered.

Technologies: [Tenda W20E](https://junglewise.ai/threats/technologies/w20e). Vendors: [Tenda](https://junglewise.ai/threats/vendors/tenda).

## Quick answers

**Is CVE-2026-36820 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-36820 being exploited in the wild.

**How severe is CVE-2026-36820?** Informational severity, with a CVSS score of 7.5, published 9 June 2026.

**Which products and versions are affected?** Tenda W20E v15.11.0.6.

**Is there a fix for CVE-2026-36820?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-36820 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2026-36820?** Check whether you run Tenda W20E at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A stack-based buffer overflow exists in the 'formAddWebAuthWhiteUser' function of the Tenda W20E v15.11.0.6 firmware. The vulnerability is triggered when the 'webAuthWhiteUserInfo' HTTP parameter, retrieved via 'websGetVar', is processed using 'strncpy' without adequate bounds checking. Specifically, the code calculates the length of the string to copy based on the position of a newline character ('\n') using 'strchr', allowing an attacker to provide a string longer than the destination buffer 'temp'. A remote attacker can exploit this by sending a crafted HTTP request to the 'addWebAuthWhiteUser' action, resulting in a process crash or device instability (Denial of Service).

## Affected products

- Tenda W20E v15.11.0.6

## Timeline

- 2026-03-19: other: CVE request submitted to MITRE
- 2026-06-06: disclosed: Public disclosure
- 2026-06-09: advisory: NVD published date

## References

- [https://github.com/xhh0124/SemVulLLM/tree/main/W20E/formAddWebAuthWhiteUser](https://github.com/xhh0124/SemVulLLM/tree/main/W20E/formAddWebAuthWhiteUser)

## Related threats

- [Tenda W20E stack buffer overflow in formDelWebAuthWhiteUser](https://junglewise.ai/threats/cve-2026-90689-tenda-w20e-stack-buffer-overflow-in-formdelwebauthwhiteuser)
- [Tenda W20E stack buffer overflow in formIPMacBindAdd](https://junglewise.ai/threats/cve-2026-90688-tenda-w20e-stack-buffer-overflow-in-formipmacbindadd)
- [Tenda W20E buffer overflow in formAddWebAuthUser](https://junglewise.ai/threats/cve-2026-36823-tenda-w20e-buffer-overflow-in-formaddwebauthuser)
- [Tenda W20E buffer overflow in formDelStaState](https://junglewise.ai/threats/cve-2026-36822-tenda-w20e-buffer-overflow-in-formdelstastate)
- [Tenda W20E buffer overflow in formCropAndSetWewifiPic](https://junglewise.ai/threats/cve-2026-36821-tenda-w20e-buffer-overflow-in-formcropandsetwewifipic)