A critical flaw in Obsidian-TC versions before 1.3.1 allows attackers with valid tokens to read, write, or delete data in any configured vault.
Key points
- CVE-2026-77366 is rated CVSS 9.9 Critical by the NVD.
- The flaw affects Obsidian-TC versions prior to 1.3.1.
- Version 1.3.1 fixes the issue by binding tokens to specific vaults.
The-40-Thieves released version 1.3.1 of Obsidian-TC to address a critical authentication bypass. This update stops attackers from accessing vaults they should not control.
What happened
The National Vulnerability Database lists CVE-2026-77366 with a CVSS score of 9.9, marking it as critical. The flaw exists in Obsidian-TC versions before 1.3.1, a Model Context Protocol server for Obsidian vaults. According to the NVD record, the server failed to compare the caller-controlled input.vault value with the vault actually bound to the caller.
Additionally, the JSON Web Token used for authentication lacked a specific vault claim. The folder access-control list was also shared globally across the system. Because of these design flaws, any valid token could select a different configured vault. Attackers could then use affected tools to read, write, or delete contents within those unauthorized vaults. The weakness is categorized under CWE-639 and CWE-863 in the NVD description.
Why it matters
This vulnerability breaks the isolation intended between different user vaults. Since the JWT did not specify which vault the token belonged to, the server could not enforce strict boundaries. An attacker with a single valid token could pivot to any other vault configured on the server. This allows for full data manipulation, including deletion, across the entire system. The global sharing of access-control lists further exacerbated the risk by removing per-vault restrictions.
The fix
- Upgrade Obsidian-TC to version 1.3.1 or later.
- Verify that new tokens are bound to specific vaults.
- Ensure the server rejects mismatched input.vault values before scope checks.
What to do and how to stay safe: Obsidian-TC
- Check your Obsidian-TC server version immediately to see if it is below 1.3.1.
- Review server logs for any unauthorized vault access or unexpected data changes.
- Rotate all JSON Web Tokens to ensure old, unscoped tokens are invalidated.
- Monitor network traffic for unusual tool dispatch requests to sensitive vaults.
Step-by-step guide: Patch Testing: How to Verify Fixes Without Breaking Your Systems
General security guidance from the Crypt Weekly newsroom. It is not confirmed advice from the organisations named in this story.
Frequently asked questions
Which versions of Obsidian-TC are affected by CVE-2026-77366?
All versions of Obsidian-TC prior to 1.3.1 are affected by this vulnerability.
How severe is this vulnerability according to the NVD?
The NVD rates CVE-2026-77366 as Critical with a CVSS score of 9.9.
Does version 1.3.1 completely fix the cross-vault access issue?
Yes, version 1.3.1 binds tokens and request context to a vault and rejects mismatched values.
