CVE-2026-6058: Zyxel WRE6505 v2 DoS Vulnerability

CVE-2026-6058 Overview

CVE-2026-6058 is an improper encoding or escaping vulnerability (CWE-116) affecting the CGI program of the Zyxel WRE6505 v2 wireless range extender. This vulnerability exists in firmware version V1.00(ABDV.3)C0 and allows an adjacent attacker on the WLAN to cause a denial-of-service (DoS) condition in the web management interface. Exploitation requires convincing an authenticated administrator to visit the "AP Select" page while a malformed SSID is present on the network.

Notably, this vulnerability was assigned while the affected product was already unsupported, meaning no official patches will be released by Zyxel.

Critical Impact

An attacker on the same wireless network can render the device's web management interface unavailable, preventing administrators from configuring or managing the range extender.

Affected Products

• Zyxel WRE6505 v2 firmware version V1.00(ABDV.3)C0
• Other firmware versions of the WRE6505 v2 may also be affected

Discovery Timeline

• 2026-04-21 - CVE CVE-2026-6058 published to NVD
• 2026-04-21 - Last updated in NVD database

Technical Details for CVE-2026-6058

Vulnerability Analysis

This vulnerability stems from improper encoding or escaping of output in the CGI program that handles the "AP Select" functionality within the Zyxel WRE6505 v2 web management interface. When the CGI program processes SSID data for display, it fails to properly sanitize or encode special characters that may be present in malformed SSIDs broadcast by nearby access points.

The attack requires adjacent network access, meaning the attacker must be within wireless range of the target device. While the vulnerability requires high privileges (an authenticated administrator must be active), no user interaction is needed from the administrator beyond normal device management activities.

Root Cause

The root cause is classified as CWE-116 (Improper Encoding or Escaping of Output). The CGI program responsible for rendering the "AP Select" page does not properly encode or escape SSID values before incorporating them into the web interface output. When a malformed SSID containing unexpected characters or sequences is encountered, the improper handling causes the web management interface to crash or become unresponsive.

Attack Vector

The attack vector requires the adversary to be on the adjacent network (WLAN). An attacker would broadcast a maliciously crafted SSID from an access point within wireless range of the target Zyxel WRE6505 v2 device. When an authenticated administrator navigates to the "AP Select" page—which enumerates available wireless networks—the malformed SSID data is processed by the vulnerable CGI program.

The improper encoding handling triggers the denial-of-service condition. The attacker does not need to authenticate to the target device; they only need to ensure their malicious SSID is visible during the network scan. This makes the attack relatively straightforward to execute for anyone within wireless range, though the impact is limited to availability of the management interface rather than data compromise or code execution.

Detection Methods for CVE-2026-6058

Indicators of Compromise

• Unusual SSIDs containing special characters, escape sequences, or malformed Unicode appearing in wireless scan results
• Web management interface becoming unresponsive or crashing when accessing the "AP Select" page
• Repeated administrator authentication attempts followed by immediate session termination

Detection Strategies

• Monitor for rogue access points broadcasting SSIDs with non-standard characters or excessive lengths
• Implement wireless intrusion detection systems (WIDS) to identify anomalous SSID broadcasts in the vicinity
• Log and analyze web management interface access patterns for anomalies in the "AP Select" functionality

Monitoring Recommendations

• Deploy network monitoring to detect unauthorized wireless access points within range of Zyxel devices
• Enable logging on the Zyxel WRE6505 v2 if available and review logs for CGI program errors
• Consider segmenting management access to limit exposure to adjacent network attacks

How to Mitigate CVE-2026-6058

Immediate Actions Required

• Replace the Zyxel WRE6505 v2 with a currently supported wireless range extender, as this product is end-of-life
• Restrict physical access to the wireless network environment to limit adjacent network attack exposure
• Disable the web management interface if remote management is not required
• Use wired management access where possible to reduce wireless attack surface

Patch Information

No patch is available. The Zyxel WRE6505 v2 was unsupported at the time this vulnerability was assigned. According to the Zyxel End of Life Policy, products that have reached end-of-life status do not receive security updates. Organizations using this device should plan for immediate replacement with a supported alternative.

Workarounds

• Deploy additional wireless access controls to prevent unauthorized devices from broadcasting malicious SSIDs
• Limit administrator access to the web management interface to trusted, wired connections only
• Implement network segmentation to isolate the range extender's management interface from untrusted wireless clients
• Consider deploying a firewall or access control list to restrict management interface access

# Example: Disable web management on alternate ports if supported
# Note: Consult device documentation for available options
# The most effective mitigation is device replacement

# Monitor for rogue SSIDs in your environment
# Linux example using iwlist
iwlist wlan0 scan | grep -E "ESSID:.*(\\x|%|<|>)"