# CVE-2026-36778: Tenda O3 Wireless Router stack overflow in R7WebsSecurityHandler

Source: https://junglewise.ai/threats/cve-2026-36778-tenda-o3-wireless-router-stack-overflow-in-r7webssecurityhandler  
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-2026-36778 · Severity: info · CVSS 7.5 · Published 2026-06-09

The Tenda O3 is a wireless router used for long-range outdoor networking. A security flaw in how the device handles login requests allows an attacker to send a specially crafted web request that crashes the device. This results in a denial-of-service, cutting off network connectivity for users and potentially requiring a manual reboot to restore operations.

Technologies: [Tenda O3 Wireless Router](https://junglewise.ai/threats/technologies/o3). Vendors: [Tenda](https://junglewise.ai/threats/vendors/tenda).

## Quick answers

**Is CVE-2026-36778 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-36778 being exploited in the wild.

**How severe is CVE-2026-36778?** Informational severity, with a CVSS score of 7.5, published 9 June 2026.

**Which products and versions are affected?** Tenda O3 Wireless Router v1.0.0.5(4180).

**Is there a fix for CVE-2026-36778?** 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-2026-36778 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2026-36778?** Check whether you run Tenda O3 Wireless Router 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 R7WebsSecurityHandler function of the Tenda O3 router (firmware v1.0.0.5). The vulnerability is located in the CGI handler where the 'username' and 'password' parameters are retrieved via websGetVar without length validation. Specifically, the 'username' input is passed to an unbounded strcpy call into a fixed-size stack buffer (aiStack_238). An unauthenticated remote attacker can exploit this by sending a crafted HTTP request with an overly long username string, leading to a device crash (Denial of Service) or potentially arbitrary code execution. The vulnerability is reachable via the default web interface.

## Affected products

- Tenda O3 Wireless Router v1.0.0.5(4180)

## Timeline

- 2026-03-10: 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/O3/R7WebsSecurityHandler](https://github.com/xhh0124/SemVulLLM/tree/main/O3/R7WebsSecurityHandler)

## Related threats

- [Tenda O3 Wireless Router stack overflow in fromNetToolGet](https://junglewise.ai/threats/cve-2026-36784-tenda-o3-wireless-router-stack-overflow-in-fromnettoolget)
- [Tenda O3 Wireless Router stack overflow in fromNetToolGet](https://junglewise.ai/threats/cve-2026-36783-tenda-o3-wireless-router-stack-overflow-in-fromnettoolget)
- [Tenda O3 Wireless Router stack overflow in fromVirtualSer](https://junglewise.ai/threats/cve-2026-36779-tenda-o3-wireless-router-stack-overflow-in-fromvirtualser)