N300 Firmware: Improper Restriction of Excessive Authentication Attempts
CVE-2026-36959 is a high-severity improper restriction of excessive authentication attempts vulnerability in N300 Firmware from U-speed, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected N300 Firmware versions: 1.0.0. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.35% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of N300 Firmware you run against the affected versions below, and install the vendor's latest release.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| U-speed | N300 Firmware | 1.0.0 | Not stated |
Version data comes from NVD's product matching. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- NoneNothing can be modified.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N. Scored by CISA (ADP).
Official description
U-SPEED N300 router V1.0.0 does not implement rate limiting or account lockout protections on the /api/login endpoint. This allows an attacker on the local network to perform unlimited authentication attempts, enabling brute-force attacks against the administrator account and potential unauthorized access to the router management interface.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Restriction of Excessive Authentication Attempts
The product does not implement sufficient measures to prevent multiple failed authentication attempts within a short time frame.
How developers prevent this class of flaw
- Common protection mechanisms include: Disconnecting the user after a small number of failed attempts Implementing a timeout Locking out a targeted account Requiring a computational task on the user's part.
- Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Consider using libraries with authentication capabilities such as OpenSSL or the ESAPI Authenticator.
More Improper Restriction of Excessive Authentication Attempts vulnerabilities (CWE-307)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: poc, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Technical write-ups (may include proof of concept)
- github.com/kirubel-cve/CVE-2026-36959Exploit, Third Party Advisory
Other vulnerabilities in N300 Firmware
- 7.5 High severity
Recent Improper Restriction of Excessive Authentication Attempts vulnerabilities
- 7.5 High severity
- 7.5 High severity
- 7.3 High severity
- 8.8 High severity
- 7.2 High severity
- 7.5 High severity
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