Description
Umbraco CMS before 17.7.1 and 18.2.1 contains a missing authorization vulnerability that allows unauthenticated clients to connect to the backoffice PreviewHub and BackofficeHub SignalR hubs. Attackers can complete the SignalR negotiate step and receive refreshed notifications that disclose content keys, including unpublished content, and reveal editorial activity timing.
References8
- github.com/umbraco/Umbraco-CMS/blob/release-18.2.0/src/Umbraco.…
- github.com/umbraco/Umbraco-CMS/blob/release-18.2.0/src/Umbraco.…
- github.com/umbraco/Umbraco-CMS/commit/243e082479c777d0f585bbd2f…
- github.com/umbraco/Umbraco-CMS/commit/b4f6cfc9d0955f9d8443e6835…
- github.com/umbraco/Umbraco-CMS/releases/tag/release-17.7.1
- github.com/umbraco/Umbraco-CMS/releases/tag/release-18.2.1
- github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-4c5q-6c…
- www.vulncheck.com/advisories/umbraco-cms-before-17.7.1-and-18.2…
Metrics
- CVSS 3.1
-
3.7
LOW
Score source: CNA
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N - CVSS 4.0
-
6.3
MEDIUM
Score source: CNA
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - EPSS — exploit probability
- 0% percentile: 24 · as of 10 November 2026
- CWE
- CWE-306
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.