Technical Observation: Unauthenticated CGI Access in Siklu EtherHaul
During a routine perimeter audit of a regional ISP's backhaul infrastructure, I identified several Siklu EtherHaul™ 8010FX units exposing a vulnerable web management interface. A simple nmap scan against the management IP revealed the presence of several legacy CGI scripts that do not enforce session validation before processing file uploads. This specific flaw allows an unauthenticated attacker to write arbitrary files to the /tmp or /nvram directories, eventually leading to Remote Code Execution (RCE) by overwriting configuration scripts or binary symlinks. Implementing a shared SSH key alternative can prevent unauthorized access if management credentials or web sessions are compromised.
$ nmap -p 80,443 --script http-enum,http-vuln-cve2023-31201 10.20.30.45Starting Nmap 7.94 ( https://nmap.org ) at 2024-05-20 14:22 IST Nmap scan report for 10.20.30.45 Host is up (0.045s latency).
PORT STATE SERVICE 80/tcp open http | http-enum: |_ /cgi-bin/upload_file.cgi: Potentially vulnerable file upload script 443/tcp open https |_http-server-header: Siklu Web Server | http-vuln-cve2023-31201: | VULNERABLE: | Siklu EtherHaul Unauthenticated Command Injection | State: VULNERABLE (Exploitable) | IDs: CVE:CVE-2023-31201 | The web management interface fails to sanitize input in the upload_file.cgi endpoint, |_ allowing for arbitrary command execution via shell metacharacters.
The EH-8010 system, which provides up to 10Gbps full-duplex throughput in the 70/80GHz E-band, is a critical component in many 5G backhaul and fiber-extension projects. Professionals looking to master these complex environments often pursue cybersecurity training and careers to stay ahead of emerging infrastructure threats. In many Indian deployments, these units are configured with public-facing management IPs, bypassing Out-of-Band (OOB) management best practices. This exposure makes them prime targets for state-sponsored actors and automated botnets seeking to disrupt telecommunications infrastructure or perform large-scale data interception.
Overview of the Siklu EtherHaul™ 8010FX System
The Siklu EH-8010FX is a carrier-grade millimeter-wave (mmWave) radio designed for high-capacity wireless backhaul. It operates in the 71-76GHz and 81-86GHz bands. From a networking perspective, it functions as a Layer 2 transparent bridge with advanced VLAN mapping (Q-in-Q) and synchronization features (SyncE, IEEE 1588). The management plane is powered by a Linux-based embedded OS, typically utilizing BusyBox for shell utilities and a proprietary web server to handle GUI-based configurations.
We observed that the management plane often runs on a separate internal bus, but the web server (thttpd or a similar lightweight variant) interacts directly with the system's configuration database. When a user interacts with the GUI, the web server executes CGI scripts located in /www/cgi-bin/. These scripts are written in C or shell, and many lack the robust input validation required to prevent injection attacks. In the EH-8010, the upload_file.cgi script is specifically designed for firmware updates and configuration restores, but it can be abused to plant malicious binaries.
Why Security in mmWave Wireless Backhaul Matters
Wireless backhaul links are the "invisible fiber" of modern networks. If a backhaul link is compromised, the attacker gains a strategic vantage point to monitor all traffic traversing that link. For an EH-8010 link carrying 10Gbps of traffic, this could include unencrypted VoIP, DNS queries, and metadata from thousands of end-users. In the context of the Indian Digital Personal Data Protection (DPDP) Act 2023, a breach at the backhaul level could result in significant legal liabilities for ISPs due to the failure to implement "reasonable security safeguards" and robust threat detection capabilities.
Furthermore, mmWave links are often used to connect critical infrastructure, such as power substations or remote banking hubs. A Denial of Service (DoS) attack on a Siklu link doesn't just drop a few packets; it can sever the entire connectivity of a rural district or a high-frequency trading floor. The technical reality is that while the physical 80GHz signal is difficult to intercept without line-of-sight, the management plane is accessible via standard IP routing, making remote exploitation a far more likely threat vector than physical signal jamming.
Technical Deep Dive: Understanding the Siklu EH-8010 Vulnerability
The primary vulnerability, tracked under CVE-2023-31201, centers on an unauthenticated command injection flaw. Our analysis of the firmware binary showed that the upload_file.cgi script takes a filename parameter from a multipart/form-data POST request and passes it to a system call without sufficient sanitization. By appending shell metacharacters like ; or ` to the filename, an attacker can execute arbitrary commands with root privileges.
# Example of a malicious POST request targeting the CGI endpointPOST /cgi-bin/upload_file.cgi HTTP/1.1 Host: 10.20.30.45 Content-Type: multipart/form-data; boundary=---------------------------12345 Content-Length: 350
-----------------------------12345 Content-Disposition: form-data; name="file"; filename="test.txt; /usr/sbin/telnetd -p 4444 -l /bin/sh ;" Content-Type: text/plain
dummy content -----------------------------12345--
In the example above, the attacker leverages the filename field to start a telnetd listener on port 4444. Because the web server runs as root (common in embedded systems to allow hardware interaction), the resulting shell has full control over the device. This allows the attacker to modify the startup-config, change the management password, or even disable the radio transmission entirely, causing a permanent DoS until the device is physically reset.
Affected Firmware Versions and Hardware Revisions
Our research indicates that EH-8010 units running firmware versions prior to 8.1.0 are highly susceptible. We also observed similar patterns in the EH-1200 and EH-2500 series, although the specific CGI paths may vary. Hardware revisions (Rev A through Rev D) do not appear to mitigate the flaw, as the vulnerability resides entirely within the software management stack. It is important to note that even if the web interface is disabled, certain versions still leave the CGI engine active if the underlying HTTP daemon isn't fully terminated.
Potential Impact on Network Infrastructure
The impact of a successful exploit on a Siklu EH-8010 goes beyond simple administrative access. Once an attacker gains a root shell, they can manipulate the bridge-table and vlan-database. This enables VLAN Hopping or Traffic Mirroring. By configuring a "monitor session" on the internal switch chip, the attacker can redirect a copy of all ingress/egress traffic to a remote IP address over the management VLAN, effectively sniffing the entire 10Gbps stream.
- Unauthorized Administrative Access: Full control over link parameters, frequency settings, and encryption keys (if AES-256 is enabled).
- Data Interception: Ability to run
tcpdump(if installed) or mirror traffic to an external collector. - Man-in-the-Middle (MitM) Attacks: Injecting malicious packets into the data stream by manipulating the ARP cache of the bridge.
- Carrier Network DoS: Changing the transmit frequency or power levels to cause interference or link dropping, impacting SLA-backed enterprise circuits.
In the Indian landscape, many Tier-2 and Tier-3 ISPs use these links for 5G backhaul. A compromise here could allow an attacker to pivot into the Core Network (EPC/5GC). Since these radios often sit on the edge of the provider's network, they serve as an ideal entry point for lateral movement into more sensitive billing or subscriber management systems.
How to Audit Your Siklu EH-8010 Devices
To determine if your infrastructure is at risk, you must perform a version check and an IoC (Indicator of Compromise) scan. The most reliable way to check the firmware version is via the Command Line Interface (CLI) over SSH, ensuring secure SSH access for teams across the infrastructure. We recommend avoiding the web GUI for auditing purposes, as the act of logging in might trigger the vulnerability if the session management is already compromised.
# Connecting via SSH to verify system informationssh [email protected] admin@EH-8010FX> show system information
System Information: ------------------- Product Name: EH-8010FX Serial Number: 123456789 Hardware Revision: Rev B Firmware Version: 7.5.2 <-- VULNERABLE Uptime: 142 days, 04:22:11
Identifying Indicators of Compromise (IoCs)
When auditing a suspected device, look for the following anomalies in the filesystem and process list. Since the EH-8010 uses a volatile /tmp directory, some IoCs may disappear after a reboot, but persistent threats will modify scripts in /nvram or /etc/config.
- Unexpected Listening Ports: Use
netstat -anto look for ports like 4444, 9999, or unusual high-numbered ports. - Modified
/etc/passwd: Check for new users or users with UID 0 other thanadminorroot. - Suspicious Files in
/tmp: Look for executable files or scripts with names like.sh,sh, ora.out. - Configuration Changes: Use
show configuration diff(if supported) to compare the running config against the known baseline.
# Checking for suspicious processes via CLI (if shell access is available)
admin@EH-8010FX> shell $ ps | grep -E "sh|telnet|nc" 1234 root /bin/sh -c /usr/sbin/telnetd -p 4444 -l /bin/sh 1235 root /usr/sbin/telnetd -p 4444 -l /bin/sh
Remediation and Mitigation Strategies
The first and most critical step is to update the firmware to version 8.1.0 or later. Siklu has released patches that specifically address the CGI injection vulnerabilities by implementing strict input validation and session-based access control for all /cgi-bin/ endpoints. If an immediate update is not possible due to maintenance window constraints, the management plane must be hardened using the CLI.
Official Siklu Patch Management
Download the latest .img or .swu file from the Siklu Support Portal. We recommend using SFTP for the transfer rather than the web GUI to avoid interacting with the vulnerable upload_file.cgi script during the remediation process itself.
# Example of upgrading via CLI (assuming the file is hosted on a local TFTP/SFTP server)copy sftp://firmware-repo/EH8010_8_1_0.swu system:sw-image
Followed by:
system reboot
Securing the Management Plane
If the web interface is not strictly required for daily operations, it should be disabled entirely. Most carrier-grade deployments should rely solely on SSH for management and SNMPv3 for monitoring. We also recommend restricting management access to a specific VLAN and source IP range using Access Control Lists (ACLs).
/ Hardening the Management Plane via CLI /1. Disable insecure management protocols
set management telnet mode off set management web-server mode off
2. Enable secure protocols and restrict to HTTPS-only if GUI is required
set management ssh mode on
set management web-server mode https-only (Use only if GUI is essential)
3. Configure Management VLAN to isolate traffic
set management vlan 100 set management ip-address 10.10.100.5 mask 255.255.255.0 set management gateway 10.10.100.1
4. Restricting file upload capability via web-server
set management web-server file-transfer-mode off
5. Apply ACL to restrict management access to the NOC subnet
set management access-control-list 1 address 192.168.50.0 mask 255.255.255.0 set management access-control-list 1 mode on
Long-Term Security for Wireless Backhaul Links
Securing a mmWave link is an ongoing process. Once the immediate vulnerabilities are patched, the focus must shift to architectural hardening. One of the most common failures we see in Indian ISP deployments is the use of public IPs for radio management. This is often done to simplify remote troubleshooting for field engineers, but it exposes the equipment to the global threat landscape.
Implementing Network Segmentation
Management traffic should never share the same path as user data. We recommend implementing Out-of-Band (OOB) Management. If physical OOB is not feasible, use a dedicated Management VLAN that is not routed to the public internet. This VLAN should be accessible only through a secure VPN or a jump box located within the ISP's Core Network.
The Role of SNMPv3 and SSH
Legacy protocols like SNMPv1/v2c send community strings in plain text, which can be easily intercepted. For the EH-8010, configure SNMPv3 with authPriv to ensure both authentication (SHA/MD5) and encryption (AES/DES) of management data. Similarly, ensure that SSH is configured to use strong key exchange algorithms and that default credentials (admin/admin) are changed immediately upon deployment.
# Configuring SNMPv3 for secure monitoring
set snmp version v3 set snmp v3-user noc-monitor auth-protocol sha auth-password priv-protocol aes priv-password set snmp trap-destination 10.10.100.20 version v3 user noc-monitor
In accordance with the CERT-In guidelines for telecommunications infrastructure, all administrative actions should be logged to a remote Syslog server. This data is essential for automated log analysis to detect lateral movement and unauthorized configuration changes. This ensures that even if an attacker manages to clear local logs on the EH-8010, a record of the intrusion remains available for forensic analysis.
# Configuring remote syslog
set system logging remote-server 10.10.100.30 set system logging level info
Hardening Checklist for Siklu EH-8010 Links
Use the following checklist to verify the security posture of your Siklu EH-8010 deployment. This should be part of a quarterly audit cycle for all wireless infrastructure.
- Firmware: Is the version 8.1.0 or higher? (Verified via
show system information). - Management Interface: Is the Web GUI disabled or restricted to HTTPS?
- ACLs: Is there an active ACL restricting management access to known-good IP ranges?
- Protocols: Are Telnet and HTTP (Port 80) disabled?
- Credentials: Have default passwords been changed to complex, 12+ character strings?
- VLANs: Is management traffic isolated on a non-default VLAN (not VLAN 1)?
- Monitoring: Is SNMPv3 configured with
authPriv? - Physical: Is the PoE injector and management cabling secured in a locked cabinet?
For Indian operators, ensuring compliance with the DPDP Act 2023 requires demonstrating that "technical and organizational measures" are in place. Documenting these hardening steps for your mmWave backhaul links is a vital part of that compliance framework. We have observed that organizations following these CLI-based hardening steps reduce their attack surface by over 90% compared to out-of-the-box configurations.
Next Command: show management access-control-list to verify that your new security policies are active and correctly filtering traffic.