Backdoor account in several Zyxel products

1) Use of hard-coded credentials

EUVDB-ID: #VU49149

Risk: Critical

CVSSv4.0: 9.3 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:A/U:Red]

CVE-ID: CVE-2020-29583

CWE-ID: CWE-798 - Use of Hard-coded Credentials

Exploit availability: Yes

Description

The vulnerability allows a remote attacker to gain full access to vulnerable system.

The vulnerability exists due to presence of hard-coded account zyfwp with an unchangeable password. A remote unauthenticated attacker can access the affected system via ssh or web interface using the hard-coded credentials and gain administrative privileges.

Successful exploitation of this vulnerability may result in complete compromise of vulnerable system.

Mitigation

Install updates from vendor's website.

Vulnerable software versions

NXC2500: before 6.10 Patch1

NXC5500: before 6.10 Patch1

ZyXEL ZLD: 4.60

CPE2.3

• cpe:2.3:h:zyxel_communications_corp:nxc2500:*:*:*:*:*:*:*:*
• cpe:2.3:h:zyxel_communications_corp:nxc5500:*:*:*:*:*:*:*:*
• cpe:2.3:h:zyxel_communications_corp:zyxel_zld:4.60:*:*:*:*:*:*:*

External links

https://ftp.zyxel.com/USG40/firmware/USG40_4.60(AALA.1)C0_2.pdf
https://businessforum.zyxel.com/discussion/5252/zld-v4-60-revoke-and-wk48-firmware-release
https://businessforum.zyxel.com/discussion/5254/whats-new-for-zld4-60-patch-1-available-on-dec-15
https://www.eyecontrol.nl/blog/undocumented-user-account-in-zyxel-products.html
https://www.zyxel.com/support/CVE-2020-29583.shtml
https://www.zyxel.com/support/security_advisories.shtml

Q & A

Can this vulnerability be exploited remotely?

Yes. This vulnerability can be exploited by a remote non-authenticated attacker via the Internet.

How the attacker can exploit this vulnerability?

The attacker would have to send a specially crafted request to the affected device in order to exploit this vulnerability.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.