Key points
- CVE-2026-77366 rates CVSS 9.9 due to missing vault claims in JWTs.
- Attackers can read, write, or delete data in any configured vault.
- Version 1.3.1 enforces token-to-vault binding and rejects mismatches.
The-40-Thieves released version 1.3.1 of Obsidian-TC to address a critical authorization bypass. The flaw, tracked as CVE-2026-77366, carries a CVSS score of 9.9. It affects all versions prior to 1.3.1. The vulnerability allows any valid token to access vaults not bound to the caller.
In plain English
Obsidian-TC is a Model Context Protocol server for Obsidian vaults. Before version 1.3.1, the system failed to verify if input matched the caller's vault. The JSON Web Token lacked a specific vault claim. Folder access lists were shared globally. This design allowed token holders to select any configured vault. They could then read, write, or delete its contents.
The background
The issue stems from weaknesses CWE-639 and CWE-863. Tool dispatch did not compare the caller-controlled input.vault value with the vault bound to the caller. The JSON Web Token had no vault claim to restrict access. The folder access-control list was shared globally across the system. Any valid token could therefore bypass intended scope restrictions.
What changes now
Version 1.3.1 fixes the vulnerability by binding tokens and request context to a vault. It rejects mismatched input.vault values before scope checks occur. This ensures that a token can only access the vault it is explicitly bound to. Users must upgrade to this version to mitigate the risk.
What to do and how to stay safe: Obsidian-TC
- Audit all instances of Obsidian-TC to confirm versions are 1.3.1 or higher.
- Review access logs for unauthorized vault selection attempts using valid tokens.
- Rotate all JSON Web Tokens after upgrading to ensure old credentials are invalidated.
- Monitor tool dispatch logs for mismatched input.vault values during the transition period.
Step-by-step guide: 7 Configuration Errors That Expose Systems to Zero-Day Exploits
General security guidance from the Vuln Post newsroom. It is not confirmed advice from the organisations named in this story.
Frequently asked questions
What is CVE-2026-77366?
It is a critical authorization bypass in Obsidian-TC versions before 1.3.1 that allows unauthorized vault access.
How does the vulnerability work?
The system fails to bind tokens to specific vaults, allowing any valid token to access any configured vault.
Is there a fix available?
Yes, version 1.3.1 fixes the issue by binding tokens to vaults and rejecting mismatched inputs.
