CVE-2023-28770: Zyxel DX5401-B0 Information Disclosure Flaw

CVE-2023-28770 Overview

CVE-2023-28770 is a sensitive information exposure vulnerability affecting the Export_Log CGI endpoint and the zcmd binary in Zyxel DX5401-B0 firmware versions prior to V5.17(ABYO.1)C0. A remote unauthenticated attacker can read system files and retrieve the supervisor password from an encrypted file on the device. The flaw is classified under CWE-200 (Exposure of Sensitive Information) and CWE-203. Exploitation requires no authentication and no user interaction, making the DX5401-B0 router series exposed to credential theft over the network.

Critical Impact
Unauthenticated remote attackers can extract the supervisor password from the device, enabling full administrative takeover when combined with the published chained remote code execution exploit.

Affected Products

Zyxel DX5401-B0 hardware (CPE: cpe:2.3:h:zyxel:dx5401-b0)
Zyxel DX5401-B0 firmware versions prior to V5.17(ABYO.1)C0
Deployments using the Export_Log CGI handler and the zcmd binary

Discovery Timeline

2023-04-27 - CVE-2023-28770 published to the National Vulnerability Database
2025-01-31 - Last updated in NVD database

Technical Details for CVE-2023-28770

Vulnerability Analysis

The vulnerability resides in two components of the DX5401-B0 firmware. The Export_Log CGI handler exposes system files to unauthenticated callers, and the zcmd binary leaks the encrypted supervisor credential store. Together, these flaws allow an attacker who can reach the device's web interface to obtain configuration data and the supervisor password. Public proof-of-concept material on Packet Storm demonstrates chaining this information disclosure with additional flaws to achieve remote code execution on the router.

Root Cause

The Export_Log endpoint fails to enforce authentication or path restrictions on file read operations. The zcmd binary stores or returns the supervisor password using an encryption scheme whose key material is recoverable from the device, defeating the protection. The combined design weakness maps to CWE-200 (sensitive information exposure) and CWE-203 (observable discrepancy that aids credential recovery).

Attack Vector

An attacker reaches the router's HTTP service over the network and issues a request to the Export_Log CGI without supplying valid credentials. The handler returns system files, including artifacts produced by zcmd that contain the encrypted supervisor password. The attacker decrypts the password offline and authenticates to the device as supervisor. The published exploit then leverages this access to execute arbitrary commands on the router operating system.

No synthetic exploit code is provided here. Refer to the Packet Storm advisory for the publicly documented exploitation chain.

Detection Methods for CVE-2023-28770

Indicators of Compromise

Unauthenticated HTTP or HTTPS requests to the Export_Log CGI endpoint on the router management interface
Successful supervisor logins from external or unexpected source IPs following anomalous web requests
Configuration changes, new administrative accounts, or firmware reflashes on DX5401-B0 devices
Outbound connections from the router to attacker-controlled hosts after suspicious Export_Log access

Detection Strategies

Inspect web server logs on DX5401-B0 devices for requests targeting Export_Log from non-management subnets
Alert on access to the management interface from WAN-side addresses where remote administration should be disabled
Correlate supervisor-level authentications with prior unauthenticated requests to the CGI within a short time window

Monitoring Recommendations

Forward router syslog and authentication events to a centralized log platform for retention and analysis
Track firmware version inventory for the DX5401-B0 fleet and flag devices still below V5.17(ABYO.1)C0
Monitor for the elevated EPSS exploitation probability associated with this CVE and prioritize patching accordingly

How to Mitigate CVE-2023-28770

Immediate Actions Required

Upgrade DX5401-B0 firmware to version V5.17(ABYO.1)C0 or later as directed by the Zyxel security advisory
Rotate the supervisor password and any reused credentials after patching, because prior values may be compromised
Audit configuration, account lists, and any custom scripts on affected devices for unauthorized changes

Patch Information

Zyxel released fixed firmware in V5.17(ABYO.1)C0, which addresses the unauthenticated file read in Export_Log and the supervisor password exposure in zcmd. Customers should download the update from the official Zyxel support portal referenced in the vendor advisory. No vendor-supplied workaround replaces the firmware update.

Workarounds

Disable remote (WAN-side) management on the DX5401-B0 until the firmware update is applied
Restrict LAN-side access to the web management interface to a dedicated administrative VLAN or host
Place the router behind a network access control list that blocks untrusted sources from reaching TCP/80 and TCP/443 on the device

bash

# Example: restrict management plane access on an upstream firewall
# Replace <mgmt_host> and <router_ip> with site-specific values
iptables -A FORWARD -p tcp -s <mgmt_host> -d <router_ip> --dport 443 -j ACCEPT
iptables -A FORWARD -p tcp -d <router_ip> --dport 443 -j DROP
iptables -A FORWARD -p tcp -d <router_ip> --dport 80  -j DROP