CISA KEV Alert: Actively Exploited RCE Flaw in Sierra Wireless Routers
CISA Adds High-Severity Sierra Wireless Router Vulnerability (CVE-2018-4063) to KEV Catalog
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Executive Summary
On December 13, 2025, the U.S. Cybersecurity and Infrastructure Security Agency (CISA) added CVE-2018-4063, a critical remote code execution (RCE) vulnerability in Sierra Wireless AirLink routers, to its Known Exploited Vulnerabilities (KEV) catalog. The addition confirms that this flaw is being actively exploited by threat actors in the wild. The vulnerability allows an authenticated attacker to upload malicious files and execute code, leading to a full compromise of the device. CISA has directed Federal Civilian Executive Branch (FCEB) agencies to remediate this vulnerability to protect federal networks from compromise.
Vulnerability Details
CVE-2018-4063 is an unrestricted file upload vulnerability affecting the web-based management interface of Sierra Wireless AirLink routers running the ALEOS firmware. The flaw has been assigned a CVSS score ranging from 8.8 to 9.9, classifying it as critical.
An attacker who has valid credentials for the router's web interface can exploit this vulnerability by sending a specially crafted HTTP request. This request allows them to upload an arbitrary file to a location on the web server from which it can be executed. Although the attack requires authentication, the prevalence of default or weak credentials in networking equipment means this is often a low barrier for attackers.
Affected Systems
The vulnerability impacts Sierra Wireless AirLink routers running specific versions of the ALEOS firmware. The vendor has previously released patches, and organizations using these devices must ensure they are running an updated firmware version. The following product lines are known to be affected:
- Sierra Wireless AirLink LS300
- Sierra Wireless AirLink GX400
- Sierra Wireless AirLink GX/ES440
- Sierra Wireless AirLink GX/ES450
- Sierra Wireless AirLink RV50
Exploitation Status
The vulnerability's inclusion in the CISA KEV catalog serves as definitive proof of active exploitation. Threat actors are known to continuously scan the internet for vulnerable edge devices like routers and gateways. Once compromised, these devices can be used as a foothold to pivot into internal corporate or operational technology (OT) networks, be co-opted into botnets, or be used to exfiltrate data.
Impact Assessment
A successful exploit of CVE-2018-4063 results in a full compromise of the Sierra Wireless router. This gives an attacker a persistent presence on the network perimeter. From this position, they can:
- Monitor, intercept, or redirect network traffic.
- Launch further attacks against the internal network.
- Use the router as a proxy to anonymize other malicious activities.
- Disrupt connectivity, which is particularly damaging if the router is used in critical infrastructure or industrial control systems (ICS) environments.
Given that these routers are often deployed in remote or hard-to-reach locations for telemetry and connectivity, a compromise can have a significant operational impact.
Cyber Observables for Detection
Security teams should hunt for signs of exploitation by analyzing web server logs on the routers.
| Type | Value | Description |
|---|---|---|
| url_pattern | POST / |
Monitor for HTTP POST requests to the web server root or other unusual endpoints, especially those containing file uploads. |
| file_name | *.sh, *.php, *.pl |
Look for files with executable script extensions being uploaded to the device via the web interface. |
| process_name | sh, bash, perl |
Suspicious shell or script interpreter processes running on the router, potentially spawned by the web server process. |
Detection & Response
- Vulnerability Scanning: Actively scan internal and external networks for Sierra Wireless AirLink routers and use authenticated scans to identify devices vulnerable to CVE-2018-4063.
- Log Analysis: Centralize and review web server logs from AirLink routers. Look for suspicious file upload attempts, especially from untrusted IP addresses or involving executable file types. D3FEND's
File Analysiscan be applied to any uploaded files. - Network Monitoring: Monitor traffic from the routers for any unusual outbound connections, which could indicate command-and-control (C2) communication or data exfiltration. D3FEND's
Outbound Traffic Filteringis a key defensive technique.
Mitigation
- Patch Immediately: The most effective mitigation is to apply the firmware updates provided by Sierra Wireless that address this vulnerability. FCEB agencies are required to do so by the deadline specified in the KEV catalog entry.
- Restrict Access: If patching is not immediately possible, restrict access to the router's management interface. It should not be exposed to the public internet. Access should be limited to a trusted management network or specific trusted IP addresses.
- Strong Credentials: Ensure that default credentials are changed and that strong, unique passwords are used for the management interface. Enable multi-factor authentication if the feature is available. Reference D3FEND countermeasure type
Harden.
Timeline of Events
MITRE ATT&CK Mitigations
Update Software
Applying firmware updates from Sierra Wireless is the primary mitigation to resolve the vulnerability.
Mapped D3FEND Techniques:
Restricting access to the router's management interface from the internet significantly reduces the attack surface.
Mapped D3FEND Techniques:
Password Policies
Enforcing strong, unique passwords and changing default credentials mitigates the 'authenticated' attack vector.
Mapped D3FEND Techniques:
D3FEND Defensive Countermeasures
The immediate and most effective countermeasure is to apply the security patches provided by Sierra Wireless for the ALEOS firmware. Given that CVE-2018-4063 is an older vulnerability, many organizations may have overlooked it. Asset management teams must prioritize identifying all deployed Sierra Wireless AirLink routers and verifying their current firmware versions against the patched versions. For devices managed by Federal agencies, this action is mandatory under CISA's directive. For private organizations, especially those in critical infrastructure sectors, this should be treated as an emergency change. A robust patch management program that includes networking and IoT devices, not just traditional servers and workstations, is essential for preventing this type of exploitation.
As a critical compensating control, especially if patching cannot be immediately deployed, organizations must implement strict inbound traffic filtering for the management interfaces of all Sierra Wireless routers. The web interface should never be exposed directly to the public internet. Use firewall rules to restrict access to a small set of trusted IP addresses, such as those from a corporate management network or a secure administrative jump host. This action directly hardens the device against external scanning and exploitation attempts. By blocking all unauthorized inbound connections to the management port (e.g., TCP/443), an external attacker cannot reach the vulnerable file upload function, effectively neutralizing the threat from outside the network perimeter.
Since the exploit requires authentication, monitoring account activity on the routers is a valuable detection strategy. Organizations should ensure that logging is enabled for all authentication events on their Sierra Wireless devices and that these logs are forwarded to a central SIEM. Create alerts for multiple failed login attempts, successful logins from unexpected geographic locations or IP addresses, and any activity from default or shared accounts. A strong password policy and the disabling of default accounts are prerequisites for this technique to be effective. By monitoring account usage, security teams can detect credential stuffing attacks or the use of compromised credentials, which are common precursors to the exploitation of authenticated vulnerabilities like CVE-2018-4063.
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Article Author
Jason Gomes
• Cybersecurity PractitionerCybersecurity professional with over 10 years of specialized experience in security operations, threat intelligence, incident response, and security automation. Expertise spans SOAR/XSOAR orchestration, threat intelligence platforms, SIEM/UEBA analytics, and building cyber fusion centers. Background includes technical enablement, solution architecture for enterprise and government clients, and implementing security automation workflows across IR, TIP, and SOC use cases.
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