What’s Vulnerable › Vulnerabilities

CVE-2026-111624: Umbraco CMS before 17.7.1 and 18.2.1 Missing Authorization on SignalR Hubs

• Severity: low (CVSS 3.7 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-16 · updated 2026-10-21
• Weakness: CWE-306

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can complete the SignalR negotiate step and receive refreshed notifications that disclose content keys, including unpublished content, and reveal editorial activity timing.

Affected products

• Umbraco-CMS: from 17.0.0 before 17.7.1; from 18.0.0 before 18.2.1 — fixed in 17.7.1, 18.2.1

How to fix

Upgrade to a fixed version: Umbraco-CMS 17.7.1, 18.2.1. Check the vendor advisory for mitigations.

References

• https://github.com/umbraco/Umbraco-CMS/blob/release-18.2.0/src/Umbraco.Cms.Api.Management/Preview/PreviewHub.cs#L9-L11
• https://github.com/umbraco/Umbraco-CMS/blob/release-18.2.0/src/Umbraco.Cms.Api.Management/Preview/PreviewHubUpdater.cs#L58
• https://github.com/umbraco/Umbraco-CMS/commit/243e082479c777d0f585bbd2f8db571607767b22
• https://github.com/umbraco/Umbraco-CMS/commit/b4f6cfc9d0955f9d8443e68353db4a692e91bd94
• https://github.com/umbraco/Umbraco-CMS/releases/tag/release-17.7.1
• https://github.com/umbraco/Umbraco-CMS/releases/tag/release-18.2.1
• https://github.com/umbraco/Umbraco-CMS/security/advisories/GHSA-4c5q-6c64-96j7
• https://www.vulncheck.com/advisories/umbraco-cms-before-17.7.1-and-18.2.1-missing-authorization-on-signalr-hubs

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