CVE-2026-27512: Tenda F3 Firmware XSS Vulnerability

CVE-2026-27512 Overview

CVE-2026-27512 is a content-type confusion vulnerability affecting the Shenzhen Tenda F3 Wireless Router firmware V12.01.01.55_multi. The administrative interface fails to include the X-Content-Type-Options: nosniff security header, and reflects attacker-influenced content into response bodies. When combined with browser MIME sniffing behavior, this can result in responses being interpreted as active HTML, enabling script execution within the context of the administrative interface.

This vulnerability is classified as Cross-Site Scripting (XSS) under CWE-79, allowing attackers to potentially execute malicious scripts when an authenticated administrator interacts with crafted content.

Critical Impact
Attackers can execute arbitrary JavaScript in the context of the router's administrative interface, potentially leading to session hijacking, credential theft, or unauthorized configuration changes on the affected Tenda F3 router.

Affected Products

Tenda F3 Firmware V12.01.01.55_multi
Tenda F3 Wireless Router (Hardware)

Discovery Timeline

February 23, 2026 - CVE-2026-27512 published to NVD
February 23, 2026 - Last updated in NVD database

Technical Details for CVE-2026-27512

Vulnerability Analysis

The vulnerability stems from improper response header configuration in the Tenda F3 administrative web interface. The router firmware fails to implement the X-Content-Type-Options: nosniff security header, which is designed to prevent browsers from MIME-sniffing a response away from the declared content-type.

When attacker-controlled input is reflected into HTTP responses without proper sanitization, and the browser performs MIME sniffing on the response, the content may be interpreted as executable HTML/JavaScript. This enables Cross-Site Scripting attacks where malicious scripts execute within the trusted context of the router's administrative interface.

The network-accessible attack vector means any attacker who can reach the router's web interface—either from the local network or potentially from the internet if remote administration is enabled—can attempt exploitation. User interaction is required, as an administrator must access a crafted URL or malicious content for the attack to succeed.

Root Cause

The root cause is twofold: First, the administrative interface omits the X-Content-Type-Options: nosniff HTTP response header, which would instruct browsers to strictly follow the declared MIME type. Second, user-supplied input is reflected into response content without adequate sanitization or encoding. Together, these issues allow attackers to craft requests that result in responses being interpreted as active content by vulnerable browsers.

Attack Vector

The attack is network-based and requires user interaction from an authenticated administrator. An attacker crafts a malicious URL or request containing script content that gets reflected in the router's HTTP response. Due to the missing nosniff header, browsers may sniff the content type and interpret the response as HTML, executing any embedded scripts.

A typical attack scenario involves:

Attacker identifies a reflection point in the Tenda F3 administrative interface
Attacker crafts a URL containing malicious JavaScript payload
Attacker delivers the URL to an authenticated administrator (via phishing, social engineering, etc.)
When the administrator accesses the URL, the router reflects the attacker's payload
The browser, performing MIME sniffing, interprets the response as HTML and executes the script
The script runs with the administrator's session privileges, enabling account compromise or configuration changes

For detailed technical information, refer to the VulnCheck Advisory on Tenda F3.

Detection Methods for CVE-2026-27512

Indicators of Compromise

Suspicious HTTP requests to the Tenda F3 administrative interface containing encoded script tags or JavaScript payloads in URL parameters
Unusual administrator session activity following access to external links
Unexpected router configuration changes without administrator action
HTTP access logs showing URLs with unusual encoded characters or script fragments

Detection Strategies

Monitor web server logs for requests containing common XSS payload patterns such as <script>, javascript:, or event handlers like onerror
Implement network intrusion detection rules to identify reflected XSS attack patterns targeting the router interface
Review HTTP response headers from the Tenda F3 interface to confirm the absence of X-Content-Type-Options: nosniff
Deploy browser-based security extensions that detect and block XSS attempts

Monitoring Recommendations

Enable detailed logging on the Tenda F3 router administrative interface if available
Monitor network traffic to the router management port for suspicious patterns
Implement egress monitoring to detect potential data exfiltration following successful exploitation
Consider placing the router management interface behind additional network access controls

How to Mitigate CVE-2026-27512

Immediate Actions Required

Restrict access to the Tenda F3 administrative interface to trusted IP addresses only
Disable remote administration features if not required
Ensure administrators do not access untrusted links while logged into the router interface
Consider placing the router behind a firewall with strict access controls to the management interface
Use dedicated browser sessions (or incognito mode) when administering the router

Patch Information

At the time of publication, no official patch from Tenda has been identified in the available CVE data. Organizations should monitor the Tenda F3 Product Page for firmware updates addressing this vulnerability. Contact Tenda support for information regarding security patches for firmware version V12.01.01.55_multi.

Workarounds

Implement network-level access controls to restrict administrative interface access to specific trusted hosts or VLANs
Deploy a reverse proxy in front of the administrative interface that adds the X-Content-Type-Options: nosniff header to all responses
Use browser security features such as Content Security Policy headers at the network level if possible
Consider replacing the affected device with a router that receives regular security updates
Educate administrators about the risks of clicking untrusted links while authenticated to network devices

bash

# Example: Restrict router admin access via firewall rules (iptables)
# Allow admin interface access only from management workstation
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.100 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP

# Example: Restrict via network ACL on upstream switch/firewall
# permit tcp host 192.168.1.100 host 192.168.1.1 eq 80
# deny tcp any host 192.168.1.1 eq 80