CVE-2021-35034Network attack vector

Unauthorized device access via nonexpiring intercepted session token

Published Dec 29, 2021 · Updated Aug 4, 2024

Insufficient session expiration in Zyxel NBG6604 firmware 1.00(ABIR.8)C0 allows remote attackers to access the device with an intercepted token. The CGI program fails to invalidate management sessions correctly, leaving an intercepted authentication token usable after its expected expiry. Exploitation requires interception of a valid token; Zyxel does not specify which device functions or data become accessible.

CVSS severity7.4
High
EPSS probability1.04%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Insufficient session expiration in Zyxel NBG6604 firmware 1.00(ABIR.8)C0 allows remote attackers to access the device with an intercepted token. The CGI program fails to invalidate management sessions correctly, leaving an intercepted authentication token usable after its expected expiry. Exploitation requires interception of a valid token; Zyxel does not specify which device functions or data become accessible.

The record

CVE
CVE-2021-35034
Published
Dec 29, 2021
Updated
Aug 4, 2024
Vendor
Zyxel Networks
Product
NBG6604 firmware
Classifications
CWE-613, T1539
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 29, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.00(ABIR.8)C0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Zyxel Networks · NBG6604 firmwareversion=1.00(ABIR.8)C0

Published CVSS scores

6.4NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:N
7.4Zyxel CorporationCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
9.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-613Insufficient Session Expiration
T1539Steal Web Session Cookie

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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