CVE-2021-3297Public exploitNetwork attack vector

Unauthenticated administrator access via client-controlled login cookie

Published Jan 26, 2021 · Updated Nov 25, 2025

Authentication bypass in Zyxel NBG2105 V1.00(AAGU.2)C0 allows remote attackers to obtain administrator access via a login cookie. The checkCookie() JavaScript function trusts the client-controlled login cookie, and login_ok.htm sets it to 1 without validating credentials. Reachability to the router's web administration interface is sufficient to access administrative configuration pages without credentials.

CVSS severity7.8
High
EPSS probability20.51%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in Zyxel NBG2105 V1.00(AAGU.2)C0 allows remote attackers to obtain administrator access via a login cookie. The checkCookie() JavaScript function trusts the client-controlled login cookie, and login_ok.htm sets it to 1 without validating credentials. Reachability to the router's web administration interface is sufficient to access administrative configuration pages without credentials.

The record

CVE
CVE-2021-3297
Published
Jan 26, 2021
Updated
Nov 25, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-287, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 26, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 25, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.2NIST NVDAV:L/AC:L/Au:N/C:C/I:C/A:C

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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 exploitPublished

Weakness, pattern, technique

CWE-287Improper Authentication
T1190Exploit Public-Facing Application

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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