CVE-2016-7836

What Is SKYSEA Client View?

SKYSEA Client View is a PC and endpoint management platform developed by Sky Co., Ltd., a Japanese software vendor. It is one of the most widely deployed endpoint management solutions in Japan, used by thousands of Japanese enterprises and government organizations to manage corporate PCs — performing asset inventory, software distribution, security policy enforcement, and IT operations. The SKYSEA client agent is installed on all managed endpoints, where it communicates with a central management server over TCP.

Endpoint management software is a high-value target because it runs as a privileged agent on every managed workstation with administrative access, communicates over internal networks to a management server, and provides broad capability to install software, execute commands, and collect data across an entire organization's PC fleet.

Overview

CVE-2016-7836 is an improper authentication vulnerability in SKYSEA Client View that allows an unauthenticated remote attacker to execute arbitrary code on endpoints running the SKYSEA client agent. The vulnerability exists in the TCP communication handling between the SKYSEA client and the management server: the client agent's network listener fails to properly authenticate connection sources, allowing any network-adjacent attacker to send crafted packets to the client's listening port and trigger code execution. Sky Co., Ltd. released a patch in December 2016. CISA added CVE-2016-7836 to the KEV catalog in October 2025, reflecting confirmed exploitation nearly a decade after disclosure.

Affected Versions

Consult Sky Co., Ltd.'s security advisory for the complete version table and upgrade instructions.

Technical Details

Root Cause: Unauthenticated TCP Client Agent Listener

CVE-2016-7836 is an improper authentication vulnerability (CWE-287) in the SKYSEA Client View agent's TCP communication module. The SKYSEA client agent runs on managed endpoints and listens on a TCP port for communications from the management server. The authentication mechanism used to verify that incoming connections originate from a legitimate SKYSEA management server is flawed or absent for certain message types or connection sequences.

Exploitation path:

1. Attacker identifies SKYSEA client listening port — the SKYSEA client agent's TCP port is reachable from the internal network (default corporate LAN)
2. Attacker sends crafted TCP packets — without valid management server credentials, the attacker sends specially crafted messages that the client agent accepts as legitimate
3. Code execution — the crafted communication causes the agent to execute arbitrary commands or code with the privileges of the SKYSEA agent process (typically SYSTEM on Windows endpoints)

Internal Network Attack Surface

CVE-2016-7836 requires network access to the SKYSEA client's listening port, which is typically only accessible from within the corporate LAN — making it an internal-lateral-movement and post-compromise escalation tool rather than a pure external exploit. However:

• Initial network access (via phishing, VPN, or another compromise) enables targeting all SKYSEA-managed endpoints in the environment
• A compromised system on the corporate LAN can enumerate and exploit all SKYSEA clients visible on the network
• A single exploited endpoint provides access to the SKYSEA agent's privileged processes on that machine

Attack Characteristics

Discovery

The vulnerability was identified and reported to Sky Co., Ltd. in 2016 through Japan's coordinated vulnerability disclosure process (JPCERT/CC coordination). JPCERT/CC issued advisory JVNVU#93383706. Sky Co., Ltd. released the patch and security notice in December 2016.

Exploitation Context

• Mass endpoint compromise via single vulnerability: Because SKYSEA Client View is deployed as an agent on all managed endpoints in an organization, a single vulnerability in the agent enables compromising every PC in the fleet from any network-adjacent position — a lateral movement force multiplier
• Japanese enterprise targeting: SKYSEA Client View's near-exclusive deployment in Japanese organizations makes CVE-2016-7836 a targeted tool for threat actors focusing on Japanese enterprises and government networks; the 2025 CISA KEV addition suggests continued active exploitation in Japan-targeted campaigns
• Delayed CISA KEV addition: The nearly 9-year gap between the 2016 patch and the 2025 KEV entry reflects the geographically concentrated deployment (Japan) and delayed discovery of active exploitation by Western threat intelligence sources; the exploitation was likely ongoing for years before CISA cataloged it
• Unpatched endpoint management agents: Endpoint management software updates are often delayed in practice because organizations worry about agent instability; SKYSEA agents running unpatched versions for years after the 2016 fix are the exploitation target

Remediation

1. Upgrade SKYSEA Client View — update all SKYSEA client agents and the management server to Ver. 12.201 or later per Sky Co., Ltd.'s security advisory. This requires updating both the server and all client endpoints.

2. Restrict network access to SKYSEA agent ports — apply host-based firewall rules on SKYSEA-managed endpoints to restrict TCP access to the SKYSEA agent's listening port to only the authorized SKYSEA management server IP address.

3. Segment the management network — place SKYSEA management server communications on a dedicated management VLAN that is not accessible from general corporate LAN segments; this limits lateral movement exploitation.

4. Audit SKYSEA agent versions — use SKYSEA's asset management features or a network scanner to enumerate all endpoints and verify they are running the patched agent version.

5. Monitor for unexpected SKYSEA communications — log and alert on TCP connections to SKYSEA agent ports from source IPs other than the authorized management server.