CVE-2021-35034

Severity: critical (CVSS 9.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.1% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-12-29 · updated 2026-06-17
Weakness: CWE-613

Description

An insufficient session expiration vulnerability in the CGI program of the Zyxel NBG6604 firmware could allow a remote attacker to access the device if the correct token can be intercepted.

Affected products

Zyxel NBG6604 firmware: before 1.00\(abir.9\)c0 — fixed in 1.00\(abir.9\)c0

How to fix

Upgrade to a fixed version: Zyxel NBG6604 firmware 1.00\(abir.9\)c0. Check the vendor advisory for mitigations.

References

https://www.zyxel.com/support/Zyxel_security_advisory_for_sensitive_information_vulnerabilities_of_NBG6604_home_router.shtml
https://www.zyxel.com/support/Zyxel_security_advisory_for_sensitive_information_vulnerabilities_of_NBG6604_home_router.shtml

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