CVE-2021-3297Nbg2105 Firmware Authentication Bypass
On Zyxel NBG2105 V1.00(AAGU.2)C0 devices, setting the login cookie to 1 provides administrator access.
Published Jan 26, 2021 · Updated Nov 25, 2025
Key Facts
Patch immediately- CVE-2021-3297 is a high-severity vulnerability (CVSS 7.8 v3.1) affecting Nbg2105 Firmware (Zyxel).
- It is exploited in the wild, listed in CIRCL KEV, Industry KEV feed since Aug 19, 2025. No public exploit code is known.
- EPSS estimates a 21% probability of exploitation in the next 30 days.
- No fixed version is listed yet; check the vendor advisory for mitigations.
- Brandefense priority: patch immediately, because it is listed as exploited in the wild.
Scores
CVSS v3.1
7.8
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
EPSS (30-day exploit likelihood)
21%
Higher than 97.4% of all scored CVEs
Exploit maturity
Proof of concept
ATLAS score
50/100
Publication score, see How it works
Exploitation Verdict
KEV listed
Aug 19, 2025
Federal due date
None
No federal due date
Ransomware use
Not reported
Attributed actors
None named
Exploit & Defence Guidance
Exploit maturity
Proof of concept
Public exploit code
1
Proof-of-concept links
In-the-wild evidence
10
Reports of active use
Advisories And Exploit References
Description
On Zyxel NBG2105 V1.00(AAGU.2)C0 devices, setting the login cookie to 1 provides administrator access.
Known-Exploited Catalog Listings
| Catalog | Added | Remediation due | Ransomware use |
|---|---|---|---|
| CIRCL KEV | Aug 19, 2025 | n/a | Not reported |
| Industry KEV feed | Aug 19, 2025 | n/a | Not reported |
Affected Products
1 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| Nbg2105 FirmwareZyxel | v1.00\(aagu.2\)c0 | n/a |
Timeline
Publicly disclosed
Jan 26, 2021
Added to CIRCL KEV
Aug 19, 2025
Added to Industry KEV feed
Aug 19, 2025
Last updated
Nov 25, 2025
Weakness Type
- CWE-287 Improper Authentication
References
- advisoryzyxel.com · SupportLandingSR.shtml
- advisoryzyxel.com · security_advisories.shtml
- exploitVulnCheck exploitation report
- exploitVulnCheck exploitation report
- exploitVulnCheck exploitation report
FAQ
Common Questions.
On Zyxel NBG2105 V1.00(AAGU.2)C0 devices, setting the login cookie to 1 provides administrator access.
Affected: Nbg2105 Firmware (Zyxel) versions v1.00\(aagu.2\)c0. The full list is in the CVE brief.
It is exploited in the wild, listed in CIRCL KEV, Industry KEV feed since Aug 19, 2025.
No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.
No public exploit code is known.
No fixed version is listed yet; check the vendor advisory for mitigations.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.
Is CVE-2021-3297 On Your Attack Surface?
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