CVE-2026-42889: Relay Obsidian Server Authentication Bypass Critical
The National Vulnerability Database has issued an advisory for CVE-2026-42889, a critical authentication bypass affecting Relay Server versions 0.9.0 through 0.9.6. This vulnerability, scored 9.1 CVSS, resides in the multi-document WebSocket endpoints of the Relay Server, which adds real-time collaboration features to Obsidian.
According to the National Vulnerability Database, when authentication is configured, WebSocket connections made without a token query parameter were mistakenly granted full server permissions. This flaw allows an unauthenticated network attacker, simply by knowing or guessing a document ID, to establish a connection to the document sync WebSocket. From there, they can read or modify document contents without requiring a valid document token.
This is a severe design flaw. The attacker’s calculus is straightforward: minimal effort for maximum impact. Defenders using Relay Server for Obsidian must understand that this isn’t just a data leak; it’s a full compromise of document integrity. The National Vulnerability Database confirms the vulnerability is fixed in version 0.9.7.
What This Means For You
- If your organization uses Relay Server for Obsidian, you are exposed to unauthenticated data exfiltration and modification. Immediately verify your Relay Server version. If you are running versions 0.9.0 through 0.9.6, you must upgrade to 0.9.7 without delay. Audit logs for any anomalous WebSocket connections or unauthorized document changes, especially if document IDs are guessable or publicly exposed.
Indicators of Compromise
| ID | Type | Indicator |
|---|---|---|
| CVE-2026-42889 | Auth Bypass | Relay Server versions 0.9.0 through 0.9.6 |
| CVE-2026-42889 | Auth Bypass | multi-document WebSocket endpoints |
| CVE-2026-42889 | Information Disclosure | read document contents without a valid document token |
| CVE-2026-42889 | Code Injection | modify document contents without a valid document token |
Written by SCW Vulnerability Desk
Source & Attribution
| Source Platform | NVD |
| Channel | National Vulnerability Database |
| Published | May 12, 2026 at 23:16 UTC |
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