CVE-2024-7261: Zyxel NWA110AX Firmware RCE Vulnerability

CVE-2024-7261 Overview

CVE-2024-7261 is a critical OS command injection vulnerability affecting multiple Zyxel access point (AP) and security router devices. The vulnerability exists due to improper neutralization of special elements in the host parameter within the CGI program. An unauthenticated attacker can exploit this flaw by sending a crafted cookie to a vulnerable device, enabling arbitrary OS command execution with the privileges of the web server process.

This vulnerability poses a significant threat to enterprise and small business networks that rely on Zyxel wireless infrastructure. Successful exploitation grants attackers full control over affected devices, potentially enabling network reconnaissance, lateral movement, data exfiltration, or establishing persistent backdoors within the network.

Critical Impact

Unauthenticated remote attackers can execute arbitrary OS commands on vulnerable Zyxel devices by sending malicious cookies, potentially leading to complete device compromise without requiring any credentials.

Affected Products

• Zyxel NWA1123ACv3 firmware version 6.70(ABVT.4) and earlier
• Zyxel WAC500 firmware version 6.70(ABVS.4) and earlier
• Zyxel WAX655E firmware version 7.00(ACDO.1) and earlier
• Zyxel WBE530 firmware version 7.00(ACLE.1) and earlier
• Zyxel USG LITE 60AX firmware version V2.00(ACIP.2) and earlier
• Multiple NWA, WAC, WAX, and WBE series access points

Discovery Timeline

• September 3, 2024 - CVE-2024-7261 published to NVD
• September 13, 2024 - Last updated in NVD database

Technical Details for CVE-2024-7261

Vulnerability Analysis

This vulnerability is classified as CWE-78 (Improper Neutralization of Special Elements used in an OS Command), commonly referred to as OS Command Injection. The flaw resides in the CGI program's handling of the host parameter, where user-supplied input is not properly sanitized before being passed to system-level command execution functions.

The vulnerable CGI program accepts input via HTTP cookies and incorporates the host parameter value into shell commands without adequate validation or escaping. This design flaw allows attackers to inject shell metacharacters and additional commands that execute in the context of the web server process, typically with elevated privileges on embedded devices.

The attack can be executed remotely over the network without any prior authentication, making it particularly dangerous for internet-facing or improperly segmented network devices. Given the widespread deployment of Zyxel access points in enterprise environments, successful exploitation could provide attackers with a foothold for further network compromise.

Root Cause

The root cause of CVE-2024-7261 is the lack of proper input validation and sanitization in the CGI program's processing of the host parameter. When the parameter value is received via a crafted cookie, it is directly concatenated or interpolated into a system command string without escaping shell metacharacters such as semicolons (;), pipes (|), backticks (`), or dollar signs ($).

This allows attackers to break out of the intended command context and inject arbitrary commands. The vulnerability demonstrates a classic command injection pattern where untrusted user input flows directly into dangerous sink functions like system(), popen(), or similar shell-invoking APIs.

Attack Vector

The attack vector is network-based and does not require authentication. An attacker can exploit this vulnerability by:

1. Crafting an HTTP request with a malicious cookie containing the host parameter
2. Injecting OS command payloads using shell metacharacters within the parameter value
3. Sending the request to the vulnerable CGI endpoint on the target Zyxel device
4. The injected commands execute with the privileges of the web server process

The attack is straightforward to execute and can be performed using standard HTTP tools. The lack of authentication requirements significantly increases the exploitability, as any attacker with network access to the device's management interface can attempt exploitation.

Typical attack payloads might include commands to establish reverse shells, download additional malware, modify device configurations, or pivot to other network resources. On embedded devices like access points, successful exploitation often results in root-level access due to the limited privilege separation common in such platforms.

Detection Methods for CVE-2024-7261

Indicators of Compromise

• Unusual outbound network connections from Zyxel devices to unknown external IP addresses
• Unexpected processes spawned by the web server process on the device
• Modified device configurations or new administrative accounts without authorized changes
• Presence of non-standard files in temporary directories or writable locations on the device
• Anomalous HTTP requests containing suspicious cookie values targeting CGI endpoints

Detection Strategies

• Deploy network intrusion detection systems (NIDS) with signatures for command injection patterns in HTTP cookie headers
• Monitor HTTP traffic to Zyxel device management interfaces for cookies containing shell metacharacters (;, |, &, `, $())
• Implement web application firewall (WAF) rules to inspect and block requests with command injection indicators
• Review device logs for unusual CGI program invocations or error messages indicating command execution failures

Monitoring Recommendations

• Enable comprehensive logging on Zyxel devices and forward logs to a centralized SIEM for correlation analysis
• Monitor for unexpected DNS queries or network traffic originating from access points to unfamiliar destinations
• Establish baseline behavior for device network connections and alert on deviations
• Conduct periodic firmware integrity verification to detect unauthorized modifications

How to Mitigate CVE-2024-7261

Immediate Actions Required

• Update all affected Zyxel devices to the latest firmware versions that address CVE-2024-7261
• Restrict network access to device management interfaces using firewall rules and network segmentation
• Disable remote management features if not required, or limit access to trusted IP addresses only
• Conduct an audit of all Zyxel devices in the environment to identify vulnerable firmware versions

Patch Information

Zyxel has released security patches addressing this vulnerability. Organizations should consult the Zyxel Security Advisory for specific firmware versions and download links for each affected product model.

The advisory provides detailed information on patched firmware versions for the complete range of affected NWA, WAC, WAX, WBE series access points, and the USG LITE 60AX security router. Organizations should prioritize patching based on device exposure and criticality.

Workarounds

• Isolate vulnerable Zyxel devices from untrusted networks using VLAN segmentation until patches can be applied
• Configure access control lists (ACLs) on upstream network devices to restrict management interface access to authorized administrator IP addresses only
• Disable the web management interface if alternative management methods (SSH, console) are available and sufficient
• Deploy a reverse proxy or WAF in front of device management interfaces to filter malicious requests

# Example: Restrict management interface access using iptables on an upstream Linux gateway
# Allow management access only from trusted admin network
iptables -A FORWARD -d <zyxel_device_ip> -p tcp --dport 80 -s 10.10.10.0/24 -j ACCEPT
iptables -A FORWARD -d <zyxel_device_ip> -p tcp --dport 443 -s 10.10.10.0/24 -j ACCEPT
iptables -A FORWARD -d <zyxel_device_ip> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <zyxel_device_ip> -p tcp --dport 443 -j DROP