Executive Summary

[{'type': 'paragraph', 'content': 'CVE-2026-4209 is a command injection vulnerability found in multiple D-Link NAS device models, including DNS-120, 202L, 315L, 320 series, 321, 322L, 323, 325, 326, 327L, 340L, 343, 345, 726-4, 1100-4, 1200-05, and 1550-04, with firmware versions up to 20260205.'}, {'type': 'paragraph', 'content': 'The vulnerability exists in several CGI functions of the /cgi-bin/account_mgr.cgi file, such as cgi_create_import_users, cgi_user_batch_create, cgi_user_set_quota, cgi_user_del, cgi_user_modify, cgi_group_set_quota, cgi_group_modify, cgi_group_add, cgi_user_add, cgi_get_modify_group_info, and cgi_chg_admin_pw.'}, {'type': 'paragraph', 'content': "In these functions, parameters like 'overwrite', 'app', 'group', 'name', 'pw', and 'member' are directly passed from user input without proper sanitization or validation. This allows remote attackers to craft malicious HTTP requests that inject and execute arbitrary operating system commands on the affected devices."}, {'type': 'paragraph', 'content': 'The exploit is remotely executable and publicly available, enabling attackers to gain unauthorized remote command execution on the vulnerable D-Link NAS devices.'}] [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]

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Impact Analysis

This vulnerability allows remote attackers to execute arbitrary operating system commands on affected D-Link NAS devices without authorization.

Successful exploitation can lead to unauthorized remote code execution, which may allow attackers to take full control of the device, manipulate or delete data, disrupt services, or use the device as a foothold for further attacks within a network.

For example, an attacker can launch a telnet daemon with shell access on the device, effectively gaining remote shell access and control.

This poses significant security risks including data breaches, service interruptions, and potential compromise of connected systems.

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Compliance Impact

I don't know

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Detection Guidance

[{'type': 'paragraph', 'content': 'This vulnerability can be detected by monitoring for suspicious HTTP POST requests targeting the vulnerable CGI endpoint /cgi-bin/account_mgr.cgi on affected D-Link NAS devices. Specifically, crafted requests that invoke functions such as cgi_create_import_users, cgi_user_batch_create, cgi_user_add, cgi_user_modify, cgi_user_del, cgi_group_add, cgi_group_modify, cgi_group_set_quota, cgi_user_set_quota, and cgi_get_modify_group_info with parameters that may contain command injection payloads.'}, {'type': 'paragraph', 'content': "A practical detection method is to look for HTTP requests containing unusual or suspicious parameters such as 'app', 'overwrite', 'name', 'group', 'member', 'pw', or 'overwrite_app' with shell command syntax or backticks, which are indicators of command injection attempts."}, {'type': 'paragraph', 'content': 'Example commands to detect exploitation attempts via network traffic inspection or logs include:'}, {'type': 'list_item', 'content': 'Using tcpdump or Wireshark to filter HTTP POST requests to /cgi-bin/account_mgr.cgi:'}, {'type': 'list_item', 'content': "tcpdump -A -s 0 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' | grep '/cgi-bin/account_mgr.cgi'"}, {'type': 'list_item', 'content': 'Searching web server logs for suspicious parameters or payloads containing backticks or shell commands, for example using grep:'}, {'type': 'list_item', 'content': "grep -iE 'app=|overwrite=|name=|group=|member=|pw=' /var/log/httpd/access_log | grep -E '`|\\$\\(|;|&&'"}, {'type': 'paragraph', 'content': 'Additionally, monitoring for unexpected open ports or services (such as telnet on unusual ports) may indicate successful exploitation, as demonstrated by the proof-of-concept that launches a telnet daemon on port 8937.'}] [1, 9]

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Mitigation Strategies

Immediate mitigation steps include:

• Restrict network access to the affected D-Link NAS devices, especially blocking external access to the /cgi-bin/account_mgr.cgi endpoint to prevent remote exploitation.
• Disable or restrict the vulnerable CGI functions if possible, or disable remote management features until a patch is applied.
• Apply the latest firmware updates from D-Link that address this command injection vulnerability as soon as they become available.
• Monitor device logs and network traffic for signs of exploitation attempts or successful attacks.
• If exploitation is suspected, isolate the affected device from the network and perform a thorough security assessment.

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