CVE-2026-11405: Web Server httpd Auth Bypass Vulnerability

CVE-2026-11405 Overview

CVE-2026-11405 is a hidden backdoor authentication vulnerability in the /bin/httpd web server binary. The login() function at offset 004c88b8 contains a secondary authentication path that bypasses the standard MD5/hash-based verification routine. When normal authentication fails, the function reads a plaintext backdoor password from the device configuration key sys.rzadmin.password and compares it directly with strcmp() against user input. A successful match grants role=2 (administrator) and establishes a valid session. The rzadmin username is never validated, so any username paired with the backdoor password produces administrative access over the network.

Critical Impact
Unauthenticated remote attackers can obtain administrator sessions on affected devices with a single HTTP request, fully compromising confidentiality, integrity, and availability.

Affected Products

Devices running the /bin/httpd web server binary containing the rzadmin backdoor code path
Firmware images exposing the sys.rzadmin.password configuration key
Refer to CERT Vulnerability Note VU#213560 for the vendor and product list

Discovery Timeline

2026-07-06 - CVE-2026-11405 published to the National Vulnerability Database (NVD)
2026-07-08 - Last updated in the NVD database

Technical Details for CVE-2026-11405

Vulnerability Analysis

The vulnerability is a hardcoded backdoor authentication path [CWE-912] embedded in the HTTP daemon that ships with the affected firmware. The login() function at address 004c88b8 implements two independent authentication branches. The first branch uses prod_encode64, PasswordToMd5, and check_rand_key to verify credentials against securely hashed values, matching the expected challenge-response flow. When the hash comparison fails, execution falls through to the backdoor branch instead of returning an authentication error.

The backdoor branch calls GetValue("sys.rzadmin.password") to retrieve a plaintext password from persistent device configuration. It then invokes strcmp() against the attacker-supplied password. Any username submitted with the request is accepted because the code never validates that the username equals rzadmin. A matching password assigns role=2, corresponding to administrative privilege, and creates a normal session cookie usable across the management interface.

Root Cause

The root cause is an intentional secondary authentication path with hardcoded credential logic [CWE-798, CWE-912]. Storing the backdoor password in a configuration key rather than a source constant does not mitigate the flaw because the comparison uses plaintext strcmp() and no role or username check gates the branch. The design decision to continue authentication after the primary hash check fails converts a fallback into an unauthenticated bypass.

Attack Vector

An attacker reaches the vulnerable endpoint over the network by sending a POST request to the management login page. The attacker supplies any username and the backdoor password value stored in sys.rzadmin.password. The web server responds with a session cookie carrying role=2, granting full administrative control. No user interaction, prior authentication, or elevated privilege is required, and the attack can be automated against internet-exposed management interfaces.

No verified public exploit code is available. Technical details on the backdoor pattern are described in CWE-912: Hidden Functionality.

Detection Methods for CVE-2026-11405

Indicators of Compromise

Successful HTTP POST requests to the device login endpoint followed immediately by administrative actions from previously unseen source addresses
Session cookies containing role=2 issued to usernames other than the expected administrator account
Configuration reads or writes referencing the sys.rzadmin.password key in device logs
New administrator accounts, firmware uploads, or configuration exports originating from external networks

Detection Strategies

Inspect HTTP access logs for authentication successes where the submitted username does not match a provisioned account
Correlate login events with subsequent privileged operations executed within the same session ID
Alert on any device management logins sourced from WAN interfaces or non-administrative subnets

Monitoring Recommendations

Forward device syslog and HTTP access logs to a centralized logging platform for retention and correlation
Monitor egress connections from affected devices for signs of post-compromise command-and-control activity
Track firmware version and configuration checksum drift across the device fleet

How to Mitigate CVE-2026-11405

Immediate Actions Required

Restrict access to the device management interface to trusted management VLANs and remove any WAN or internet exposure
Rotate the value stored in sys.rzadmin.password and audit configuration exports for prior exposure of that key
Review authentication and audit logs for administrative sessions established without a matching provisioned account
Reset all administrative credentials and invalidate active sessions on affected devices

Patch Information

No vendor patch information is listed in the NVD entry at time of publication. Consult the coordinated advisory at CERT VU#213560 for vendor status updates and firmware release notes. Apply firmware updates that remove the rzadmin code path in /bin/httpd as soon as they are made available.

Workarounds

Block inbound TCP access to the HTTP and HTTPS management ports at the network perimeter
Place affected devices behind a VPN or bastion host that enforces multi-factor authentication
Disable remote management features where the device supports doing so through the local console
If the configuration schema permits, clear or overwrite sys.rzadmin.password with a long random value not shared across the fleet

bash

# Example perimeter filter restricting management access to a trusted subnet
iptables -A INPUT -p tcp --dport 443 -s 10.10.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP
iptables -A INPUT -p tcp --dport 80  -s 10.10.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80  -j DROP