What is the CVSS score of CVE-2026-42889?

CVE-2026-42889 has a CVSS 3.1 base score of 9.1 (Critical). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N. EPSS exploitation probability: 0.0%.

Which versions of Relay Server are affected by CVE-2026-42889?

Relay Server versions 0.9.0-0.9.6 (Obsidian real-time collaboration backend) contain a critical authentication bypass allowing unauthorized read and modification of any synced document by network…. A patch is available.

How to fix or mitigate CVE-2026-42889?

Within 24 hours, identify any instances of Relay Server versions 0.9.0-0.9.6 in your infrastructure and assess which documents are actively synced. Within 7 days, apply the patch available per vendor advisory to all affected instances, ensuring all servers are updated to versions above 0.9.6, and verify the update by testing multi-document WebSocket connections with invalid tokens to confirm rejection. Within 30 days, conduct a security audit of any documents synced during the vulnerable period to detect unauthorized access or modifications, and review access control policies for the Relay deployment to ensure token validation is enforced on all WebSocket connections.

Relay Server CVE-2026-42889

EUVD-2026-29792 CRITICAL

Incorrect Authorization (CWE-863)

2026-05-12 GitHub_M

Authentication Bypass Relay Server

9.1

CVSS 3.1 · GitHub Advisory

Severity by source

GitHub Advisory PRIMARY

9.1 CRITICAL

AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

vuln.today AI

9.1 CRITICAL

Network-reachable WebSocket, no auth or interaction, fail-open grants full read/write to documents (C:H/I:H); no availability impact and no scope change, so A:N/S:U.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Primary rating from GitHub Advisory.

CVSS VectorGitHub Advisory

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

None

Lifecycle Timeline

Analysis Generated

Jul 23, 2026 - 19:39 vuln.today

Patch available

May 12, 2026 - 21:03 EUVD

CVE Published

May 12, 2026 - 19:30 nvd

CRITICAL 9.1

DescriptionGitHub Advisory

Relay adds real-time collaboration to Obsidian. Relay Server versions 0.9.0 through 0.9.6 contain an authentication bypass in the multi-document WebSocket endpoints. When authentication is configured, WebSocket connections without a token query parameter were incorrectly treated as having full server permissions. An unauthenticated network attacker who knows or guesses a document ID could connect to the document sync WebSocket and read or modify document contents without a valid document token. This vulnerability is fixed in 0.9.7.

AnalysisAI

Authentication bypass in Relay Server 0.9.0-0.9.6 (the real-time collaboration backend for the Obsidian Relay plugin) lets unauthenticated network attackers read and modify synced documents. When authentication is enabled, the multi-document WebSocket endpoints incorrectly treated connections lacking a token query parameter as fully privileged, so anyone who knows or guesses a document ID can join the sync session without a valid document token. Publicly available exploit code exists per SSVC (POC), but EPSS is very low (0.04%) and it is not listed in CISA KEV, so there is no confirmed active exploitation.

Technical ContextAI

Relay Server implements collaborative document synchronization for Obsidian over WebSocket connections, distributing document changes in real time to connected clients. Authorization is intended to be enforced per-document via a token supplied as a WebSocket query parameter. The flaw is a CWE-863 Incorrect Authorization defect: a fail-open logic error in the multi-document WebSocket endpoints treated the absence of a token parameter as equivalent to holding full server permissions rather than rejecting the connection. The affected component is identified by CPE cpe:2.3:a:no-instructions:relay-server, confirming the vendor namespace 'no-instructions' and the relay-server product.

RemediationAI

Vendor-released patch: upgrade Relay Server to 0.9.7, which corrects the WebSocket authorization logic; this is the primary and complete fix per advisory GHSA-9vp9-8q9j-8mqm (https://github.com/No-Instructions/relay-server/security/advisories/GHSA-9vp9-8q9j-8mqm). If an immediate upgrade is not possible, restrict network reachability of the WebSocket endpoints by placing the server behind a VPN or firewall and limiting access to trusted client IP ranges, accepting that this breaks access for legitimate remote collaborators; additionally ensure document IDs are long, high-entropy, and non-enumerable to raise the guessing barrier, though this is a hardening measure and not a substitute for the patch. Rotate or re-provision any document IDs believed to have been exposed while running a vulnerable version.