# CVE-2026-42889: Relay Server WebSocket authentication bypass when token is omitted

> Unauthenticated attackers can read or modify document contents via WebSocket connections if authentication is configured but tokens are omitted.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 12 May 2026
- **Updated:** 13 May 2026
- **Also known as:** GHSA-9vp9-8q9j-8mqm

## What is CVE-2026-42889?

CVE-2026-42889 is a critical authentication bypass vulnerability in No-Instructions relay-server, published on 12 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-863 (Incorrect Authorization), CWE-639 (Authorization Bypass Through User-Controlled Key)

## Which versions are affected by CVE-2026-42889?


## How do I fix CVE-2026-42889?

No fix has been published for CVE-2026-42889 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-42889 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42889 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-42889 and fix it if it is affected.

What it is: CVE-2026-42889 is a critical authentication bypass vulnerability in No-Instructions relay-server, published on 12 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42889 exists.

Affected product: No-Instructions relay-server. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-42889/ (Markdown: https://insights.sbomify.com/CVE-2026-42889/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-42889
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-42889
- OSV: https://osv.dev/vulnerability/CVE-2026-42889

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-42889/
Summaries are generated and may contain mistakes; the official description above is the record.