No exploitation reportedFix available

CVE-2021-35034

Q: Is CVE-2021-35034 actively exploited?

Active exploitation of CVE-2021-35034 has not been confirmed. Its EPSS score was 1.1% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

Q: What is the CVSS score for CVE-2021-35034?

CVE-2021-35034 has a CVSS v3 base score of 9.1 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.

No exploitation reported by the sources we read.

Published2021-12-29
Fixed in1.00\(abir.9\)c0
WeaknessCWE-613

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC

2021-12-2913:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-35034?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-35034?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Zyxel nbg6604 firmwareversion to verify

Branch	Affected	Fixed in	Source
1.0	< 1.00\(abir.9\)c0	1.00\(abir.9\)c0	NVD

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Update Zyxel nbg6604 firmware to 1.00\(abir.9\)c0

Advisories and patches

www.zyxel.comVendor Advisory

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

CNACVSS 3.17.4read 2026-10-23
NVDCVSS 3.19.1read 2026-10-23
NVDCVSS 2.06.4read 2026-10-23
CNAweakness (CWE)CWE-613read 2026-10-23
NVDweakness (CWE)CWE-613read 2026-10-23
FIRST EPSSEPSS score1.1 %2026-10-22

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Published: 2021-12-29
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-35034?

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.

Is CVE-2021-35034 actively exploited?

Active exploitation of CVE-2021-35034 has not been confirmed. Its EPSS score was 1.1% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-35034?

CVE-2021-35034 has a CVSS v3 base score of 9.1 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N.

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