==================================================================== CERT-Renater Note d'Information No. 2020/VULN092 _____________________________________________________________________ DATE : 25/02/2020 HARDWARE PLATFORM(S): ZyXEL NAS. OPERATING SYSTEM(S): Zyxel NAS products running firmware version 5.21 and earlier. ===================================================================== https://www.zyxel.com/support/remote-code-execution-vulnerability-of-NAS-products.shtml https://kb.cert.org/vuls/id/498544/ ________________________________________________________________________ Zyxel security advisory for the remote code execution vulnerability of NAS products CVE: CVE-2020-9054 Summary Zyxel NAS (Network Attached Storage) products are affected by a remote code execution vulnerability. Users are advised to install the hotfixes or follow the workaround immediately for optimal protection. What is the vulnerability? A remote code execution vulnerability was identified in the weblogin.cgi program of Zyxel NAS products running firmware version 5.21 and earlier. Missing authentication for the program could allow attackers to perform remote code execution via OS command injection. What products are vulnerable—and what should you do? After a thorough investigation, we’ve identified the vulnerable products that are within their warranty and support period, as shown in the table below. For optimal protection, we urge users to install the hotfixes first and the firmware patches when available.. Affected model Hotfix availability Standard availability NAS326 March 2020. Firmware V5.21(AAZF.7)C0 NAS520 March 2020. Firmware V5.21(AASZ.3)C0 NAS540 March 2020. Firmware V5.21(AATB.4)C0 NAS542 March 2020. Firmware V5.21(ABAG.4)C0 For affected products that reached end-of-support in 2016 or earlier, firmware updates are no longer provided. We strongly recommend that users follow the workaround procedure, as detailed below, to remediate the vulnerability. Affected models that are end-of-support Workaround NSA210, NSA220, NSA220+, NSA221, NSA310, NSA310S, NSA320, NSA320S, NSA325 and NSA325v2 Do not leave the product directly exposed to the internet. If possible, connect it to a security router or firewall for additional protection. Got a question or a tipoff? Please contact your local service rep for further information or assistance. If you’ve found a vulnerability, we want to work with you to fix it—contact security@zyxel.com.tw and we’ll get right back to you. Acknowledgment Thanks to Brian Krebs, an independent investigative journalist, for reporting the issue to us and CERT/CC for coordinating the disclosure process. Revision history Initial release 2020-02-24 _____________________________________________________________________ ZyXEL NAS pre-authentication command injection in weblogin.cgi Vulnerability Note VU#498544 Original Release Date: 2020-02-24 | Last Revised: 2020-02-24 Overview Multiple ZyXEL network-attached storage (NAS) devices contain a pre-authentication command injection vulnerability, which may allow a remote, unauthenticated attacker to execute arbitrary code on a vulnerable device. Description CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection') ZyXEL NAS devices achieve authentication by using the weblogin.cgi CGI executable. This program fails to properly sanitize the username parameter that is passed to it. If the username parameter contains certain characters, it can allow command injection with the privileges of the web server that runs on the ZyXEL device. Although the web server does not run as the root user, ZyXEL devices include a setuid utility that can be leveraged to run any command with root privileges. As such, it should be assumed that exploitation of this vulnerability can lead to remote code execution with root privileges. Exploit code for this vulnerability is available on the internet. For this reason, we have created a PoC exploit that has the ability to power down affected ZyXEL devices. Impact By sending a specially-crafted HTTP POST or GET request to a vulnerable ZyXEL device, a remote, unauthenticated attacker may be able to execute arbitrary code on the device. This may happen by directly connecting to a device if it is directly exposed to an attacker. However, there are ways to trigger such crafted requests even if an attacker does not have direct connectivity to a vulnerable devices. For example, simply visiting a website can result in the compromise of any ZyXEL device that is reachable from the client system. Solution Apply an update ZyXEL has made firmware updates available for NAS326, NAS520, NAS540, and NAS542 devices. Owners of NSA210, NSA220, NSA220+, NSA221, NSA310, NSA310S, NSA320, NSA320S, NSA325 and NSA325v2 will not be able to install firmware updates, as these devices are no longer supported. Be cautious when updating firmware on affected devices, as the ZyXEL firmware upgrade process both uses an insecure channel (FTP) for retrieving updates, and the firmware files are only verified by checksum rather than cryptographic signature. For these reasons, any attacker that has control of DNS or IP routing may be able to cause a malicious firmware to be installed on a ZyXEL device. Please also consider the following workarounds: Block access to the ZyXEL device web interface This issue can be mitigated by blocking (for example with a firewall) access to the web interface (80/tcp and 443/tcp) of any vulnerable ZyXEL device. Any machine that can access the ZyXEL web interface should not also be able to access the internet. Restrict access to vulnerable ZyXEL devices Direct exploitation of this vulnerability can be mitigated by restricting access to vulnerable devices. In particular, do not expose such devices directly to the internet. Note however, that it is still possible for attackers to exploit devices that are not directly connected to the internet. For example, by way of viewing a web page. Vendor Information Zyxel Notified: February 15, 2020 Updated: February 24, 2020 Status Affected Vendor Statement No statement is currently available from the vendor regarding this vulnerability. Vendor Information We are not aware of further vendor information regarding this vulnerability. Vendor References https://www.zyxel.com/support/remote-code-execution-vulnerability-of-NAS-products.shtml CVSS Metrics Group Score Vector Base 10 AV:N/AC:L/Au:N/C:C/I:C/A:C Temporal 9.5 E:F/RL:U/RC:C Environmental 7.1 CDP:ND/TD:M/CR:ND/IR:ND/AR:ND References https://www.zyxel.com/support/remote-code-execution-vulnerability-of-NAS-products.shtml https://krebsonsecurity.com/2020/02/zyxel-fixes-0day-in-network-storage-devices/ https://cwe.mitre.org/data/definitions/78.html Acknowledgements Thanks to Brian Krebs for notifying us of the exploit availability, which was uncovered by Alex Holden of Hold Security. This document was written by Will Dormann. Other Information CVE IDs: CVE-2020-9054 Date Public: 2020-02-12 Date First Published: 2020-02-24 Date Last Updated: 2020-02-24 17:31 UTC Document Revision: 31 ========================================================= + CERT-RENATER | tel : 01-53-94-20-44 + + 23/25 Rue Daviel | fax : 01-53-94-20-41 + + 75013 Paris | email:cert@support.renater.fr + =========================================================