CVE-2018-4063 is a remote code execution vulnerability discovered in the Sierra Wireless AirLink ALEOS routers, particularly affecting the ACEManager's upload.cgi functionality. The flaw stems from an unrestricted file upload mechanism that lacks proper validation and access controls, allowing an authenticated attacker to upload files with arbitrary names. If the uploaded file overwrites an existing executable file on the device, such as fw_upload_init.cgi or fw_status.cgi, the attacker can execute arbitrary code with root privileges because ACEManager runs as root. This vulnerability was initially reported by Cisco Talos in 2018 and publicly disclosed in 2019. Despite its age, active exploitation has been observed recently, leading CISA to add it to its Known Exploited Vulnerabilities catalog in December 2025. Attackers exploit this by sending specially crafted HTTP requests to the /cgi-bin/upload.cgi endpoint, uploading malicious payloads that can compromise the router and potentially the broader network. The vulnerability is particularly dangerous in operational technology (OT) environments where these routers are prevalent, as attackers can deploy botnets or cryptocurrency miners, disrupt communications, or gain persistent access. The vulnerability is compounded by the end-of-support status of affected devices, limiting vendor patches and increasing exposure. A threat cluster named Chaya_005 was observed weaponizing this flaw in early 2024, although no recent successful exploits have been reported. The vulnerability's exploitation requires authentication but can lead to full device compromise and lateral movement within networks.

For European organizations, especially those operating critical infrastructure, manufacturing, transportation, and utilities, this vulnerability poses a significant risk. Sierra Wireless AirLink ALEOS routers are commonly deployed in industrial and operational technology environments across Europe. Successful exploitation can lead to complete compromise of the router, enabling attackers to execute arbitrary commands with root privileges, potentially disrupting network communications, exfiltrating sensitive data, or deploying malware such as botnets or cryptocurrency miners. This can result in operational downtime, financial losses, reputational damage, and regulatory penalties under frameworks like GDPR and NIS Directive. The vulnerability's presence in OT environments raises concerns about safety and reliability of critical services. Additionally, the end-of-support status of affected devices complicates remediation efforts, increasing the window of exposure. Attackers leveraging this flaw can also use the compromised routers as pivot points for broader network intrusions, escalating the threat to enterprise IT environments connected to OT networks.

European organizations should prioritize immediate mitigation steps beyond generic patching advice. First, identify all Sierra Wireless AirLink ALEOS routers in use, especially versions known to be vulnerable (e.g., firmware 4.9.3). Since affected devices have reached end-of-support, organizations should plan for device replacement with supported models that have patched this vulnerability. Where replacement is not immediately feasible, implement strict network segmentation to isolate vulnerable routers from critical systems and limit access to management interfaces. Enforce strong authentication and access controls on router management portals, including multi-factor authentication where possible. Monitor network traffic for anomalous HTTP requests targeting /cgi-bin/upload.cgi and unusual file upload activities. Deploy intrusion detection/prevention systems (IDS/IPS) tuned to detect exploitation attempts of CVE-2018-4063. Conduct regular audits of router firmware versions and configurations. Engage with vendors for any available security advisories or mitigations. Finally, incorporate these routers into incident response plans, preparing for potential compromise scenarios.