CVE-2023-20073: Cisco RV340 Auth Bypass Vulnerability

CVE-2023-20073 Overview

A critical arbitrary file upload vulnerability exists in the web-based management interface of Cisco RV340, RV340W, RV345, and RV345P Dual WAN Gigabit VPN Routers. This vulnerability allows an unauthenticated, remote attacker to upload arbitrary files to an affected device due to insufficient authorization enforcement mechanisms in the context of file uploads. An attacker could exploit this vulnerability by sending a crafted HTTP request to an affected device, potentially leading to complete device compromise.

Critical Impact

Unauthenticated remote attackers can upload arbitrary files to vulnerable Cisco routers, potentially enabling remote code execution, persistent backdoor installation, and complete network perimeter compromise.

Affected Products

• Cisco RV340 Dual WAN Gigabit VPN Router (all firmware versions)
• Cisco RV340W Dual WAN Gigabit Wireless-AC VPN Router (all firmware versions)
• Cisco RV345 Dual WAN Gigabit VPN Router (all firmware versions)
• Cisco RV345P Dual WAN Gigabit POE VPN Router (all firmware versions)

Discovery Timeline

• April 5, 2023 - CVE-2023-20073 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-20073

Vulnerability Analysis

This vulnerability stems from a fundamental weakness in the authorization enforcement mechanisms within the web-based management interface of affected Cisco Small Business routers. The file upload functionality fails to properly validate whether incoming HTTP requests originate from authenticated administrative sessions before processing upload operations.

The flaw is classified under CWE-434 (Unrestricted Upload of File with Dangerous Type), indicating that the web interface accepts file uploads without adequate restrictions on the file type, content, or destination path. This creates an opportunity for attackers to upload malicious files such as web shells, configuration files, or firmware images that could be leveraged to execute arbitrary code or modify device behavior.

The vulnerability is particularly dangerous because it requires no authentication, meaning any attacker with network access to the management interface can exploit it. Combined with the network-accessible attack vector and the potential for high impact across confidentiality, integrity, and availability, this vulnerability presents a significant risk to organizations using these devices.

Root Cause

The root cause of CVE-2023-20073 is insufficient authorization enforcement in the web-based management interface's file upload handler. The affected code path processes HTTP requests containing file upload payloads without first verifying that the request originates from an authenticated and authorized administrative session. This authorization bypass allows unauthenticated users to access functionality that should be restricted to device administrators only.

Attack Vector

The attack vector for CVE-2023-20073 is network-based, requiring only that an attacker can reach the web-based management interface of a vulnerable router. The exploitation process involves:

1. Reconnaissance: Identifying exposed Cisco RV340/RV345 series routers with accessible management interfaces
2. Crafted Request: Constructing an HTTP request that bypasses authentication checks in the file upload mechanism
3. File Upload: Delivering a malicious payload (such as a web shell or modified configuration file) to the device
4. Execution/Persistence: Leveraging the uploaded file to achieve code execution or maintain persistent access

The vulnerability does not require user interaction or any privileges, making it trivially exploitable once an attacker identifies a vulnerable target. Attackers may target devices with management interfaces exposed to the internet or pivot through compromised internal networks to reach otherwise protected devices.

Detection Methods for CVE-2023-20073

Indicators of Compromise

• Unexpected files appearing in router file systems, particularly in web-accessible directories or configuration locations
• Anomalous HTTP POST requests to the management interface containing file upload payloads from unauthorized sources
• Unauthorized configuration changes or unexpected firmware modifications on affected devices
• Unusual outbound network connections from the router indicating potential command and control communication

Detection Strategies

• Monitor HTTP traffic to router management interfaces for POST requests containing multipart form data from unauthenticated sessions
• Implement network-based intrusion detection rules to identify exploitation attempts targeting Cisco RV340/RV345 management interfaces
• Deploy file integrity monitoring on router file systems to detect unauthorized file additions or modifications
• Review web server logs on affected devices for suspicious upload requests or access patterns

Monitoring Recommendations

• Enable comprehensive logging on all Cisco RV340/RV345 series devices and forward logs to a centralized SIEM platform
• Establish baseline network behavior for management interface traffic and alert on deviations
• Implement continuous vulnerability scanning to identify exposed management interfaces across the network perimeter
• Monitor for publicly released exploit code or proof-of-concept tools targeting this vulnerability

How to Mitigate CVE-2023-20073

Immediate Actions Required

• Restrict access to the web-based management interface by implementing access control lists (ACLs) to limit connections to trusted administrative IP addresses
• Disable remote management access from untrusted networks, particularly the internet-facing WAN interface
• Review device file systems for any unauthorized files that may indicate prior compromise
• Implement network segmentation to isolate management interfaces from general user traffic

Patch Information

Cisco has published a security advisory addressing this vulnerability. Organizations should consult the Cisco Security Advisory for detailed patch information and firmware update instructions. It is critical to apply vendor-provided patches as soon as they become available to fully remediate this vulnerability.

Note: The Cisco RV340 series routers have reached end-of-life status, and Cisco may not provide software updates for these products. Organizations should evaluate migration to supported hardware if patches are not available.

Workarounds

• Configure the router's firewall to block HTTP/HTTPS access to the management interface from untrusted networks
• Use a VPN to access the management interface rather than exposing it directly to the network
• Implement additional network-based access controls using an external firewall or security appliance
• Consider replacing end-of-life devices with current, supported models that receive regular security updates

# Example: Restrict management interface access (configure on upstream firewall)
# Block external access to router management ports
iptables -A INPUT -p tcp --dport 443 -s 0.0.0.0/0 -d <ROUTER_MGMT_IP> -j DROP
iptables -A INPUT -p tcp --dport 80 -s 0.0.0.0/0 -d <ROUTER_MGMT_IP> -j DROP

# Allow only trusted admin subnet
iptables -A INPUT -p tcp --dport 443 -s <TRUSTED_ADMIN_SUBNET> -d <ROUTER_MGMT_IP> -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -s <TRUSTED_ADMIN_SUBNET> -d <ROUTER_MGMT_IP> -j ACCEPT