Zyxel security advisory for cleartext storage of information vulnerability

CVEs: CVE-2021-35036


Zyxel is releasing patches addressing a cleartext storage of information vulnerability in its products. Users are advised to install the patches for optimal protection.


What is the vulnerability?

The cleartext storage of information vulnerability is due to a CGI program lacking proper protection of the device’s login privilege and TR-069 configuration. The vulnerability cannot be exploited unless the attacker can first be successfully authenticated and log in to the device’s management interface. The TR-069 protocol is not enabled by default in the generic version of the firmware; therefore, it cannot be exploited by attackers.


What versions are vulnerable-and what should you do?

After a thorough investigation, we have identified the vulnerable products that are within their vulnerability support period, with their firmware patches shown in the table below.

Affected series/models Patch availability*
DSL/Ethernet CPE
VMG3625-T50B Customized firmware version V5.50(ABTL.0)b2r
EMEA: V5.50(ABPM.7)C0
Central America: V5.50(ACCR.0)b4
VMG3927-T50K V5.50(ABOM.8)C0
VMG8623-T50B V5.50(ABPM.7)C0
VMG8825-T50K V5.50(ABOM.8)C0
EMG3525-T50B V5.50(ABPM.7)C0
EMG5523-T50B V5.50(ABPM.7)C0
EMG5723-T50K V5.50(ABOM.8)C0
DX3301-T0 V5.50(ABVY.3)C0
DX5401-B0 V5.17(ABYO.2)C0
EX5401-B0 V5.17(ABYO.2)C0
EX5501-B0 V5.17(ABRY.3)C0
LTE3301-PLUS V1.00(ABQU.6)C0 in Dec. 2022
LTE5388-M804 V1.00(ABSQ.4)C0 in Dec. 2022
LTE5388-S905 V1.00(ABVI.6)C0 in Dec. 2022
LTE5398-M904 V1.00(ABQV.2)C0 in Dec. 2022
LTE7240-M403 V2.00(ABMG.6)C0 in Dec. 2022
LTE7461-M602 V2.00(ABQN.6)C0 in Dec. 2022
LTE7480-S905 V2.00(ABQT.6)C0 in Dec. 2022
LTE7480-M804 V1.00(ABRA.6)C0 in Dec. 2022
LTE7485-S905 V1.00(ABVN.6)C0 in Dec. 2022
LTE7490-M804 V1.00(ABQY.5)C0 in Dec. 2022
NR5101 V1.00(ABVC.6)C0 in Dec. 2022
NR7101 V1.00(ABUV.7)C0 in Dec. 2022
NR7102 V1.00(ABYD.2)C0 in Dec. 2022
Fiber ONT
AX7501-B Series V5.17(ABPC.2)C0
EP240P V5.40(ABVH.0)C0a03
PMG5617GA V5.40(ABNA.2)C0
PMG5622GA V5.40(ABNB.2)C0
PMG5317-T20B V5.40(ABKI.4)C0
PMG5617-T20B2 V5.41(ACBB.1)C0
PM7300-T0 V5.42(ACBC.1)C0
*Please contact your sales representative or support team for the file.


Got a question?

If you are an ISP with customized models, please contact your Zyxel sales or service representative for further information or assistance. For end-user who acquired your Zyxel device from an ISP, please reach out to the ISP’s support team directly, as the device may have custom-built settings.



Thanks to M.nageh for reporting the issue to us.


Revision history

2022-09-27: Initial release