FortiOS: Authentication Bypass by Primary Weakness
CVE-2026-126253 is a critical-severity authentication bypass by primary weakness vulnerability in FortiOS from Fortinet, with a CVSS 3.1 base score of 9.3 out of 10. It can be exploited from the same local network by an unauthenticated attacker, without any action from a user. Affected FortiOS versions: 8.0.0 through 8.0.1; 7.6.0 through 7.6.7; 7.4.0 through 7.4.12, and others listed below. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.37% chance of exploitation within 30 days, which is low compared with other CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Check which version of FortiOS you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on fortiguard.fortinet.com for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Fortinet | FortiOS | 8.0.0 through 8.0.1; 7.6.0 through 7.6.7; 7.4.0 through 7.4.12; 7.2.0 through 7.2.13; 7.0.1 through 7.0.19 | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- AdjacentThe attacker must be on the same local network segment.
- 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
- ChangedThe attack can reach beyond the vulnerable component into other systems.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:H/A:H. Scored by CNA (fortinet.com).
Official description
A authentication bypass by primary weakness vulnerability in Fortinet FortiOS 8.0.0 through 8.0.1, FortiOS 7.6.0 through 7.6.7, FortiOS 7.4.0 through 7.4.12, FortiOS 7.2.0 through 7.2.13 may allow an unauthenticated attacker to broadcast LSA via specially crafted request
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Authentication Bypass by Primary Weakness
The authentication algorithm is sound, but the implemented mechanism can be bypassed as the result of a separate weakness that is primary to the authentication error.
More Authentication Bypass by Primary Weakness vulnerabilities (CWE-305)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Other vulnerabilities in FortiOS
- 9.8 Critical severity
- 7.5 High severity
- 7.4 High severity
- 7.4 High severity
- 9.6 Critical severity
- 8.1 High severity
Recent Authentication Bypass by Primary Weakness vulnerabilities
- 8.1 High severity
- 9.8 Critical severity
- 9.0 Critical severity
- 9.1 Critical severity
- 9.1 Critical severity
- 9.1 Critical severity
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