GMS: Improper Certificate Validation
CVE-2026-66154 is a high-severity improper certificate validation vulnerability in GMS from SonicWall, with a CVSS 3.1 base score of 8.3 out of 10. It can be exploited from the same local network by an unauthenticated attacker, without any action from a user. Affected GMS versions: 9.5.1 and earlier versions. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.2% 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 GMS you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on psirt.global.sonicwall.com for workarounds and exact fixed builds.
Affected products and versions
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
- HighSuccess depends on conditions outside the attacker's control.
- 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
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H. Scored by CISA (ADP).
Official description
An insufficient certificate validation in a privileged communication workflow, was identified in a GMS application 9.5.1 (Build 9510.1044) and earlier versions which, under a successful MitM attack and controlled network conditions, could permit unauthorized changes.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Certificate Validation
The product does not validate, or incorrectly validates, a certificate.
How developers prevent this class of flaw
- Certificates should be carefully managed and checked to assure that data are encrypted with the intended owner's public key.
- If certificate pinning is being used, ensure that all relevant properties of the certificate are fully validated before the certificate is pinned, including the hostname.
More Improper Certificate Validation vulnerabilities (CWE-295)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Other vulnerabilities in GMS
- 9.4 Critical severity
- 8.4 High severity
- 9.1 Critical severity
- 7.5 High severity
- 7.1 High severity
- 9.8 Critical severity
Recent Improper Certificate Validation vulnerabilities
- 9.1 Critical severity
- 8.1 High severity
- 7.4 High severity
- 9.1 Critical severity
- 7.4 High severity
- 7.5 High severity
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