Vulnerability · Published Nov 3, 2026 · Assigned by VulnCheck

CVE-2026-121458Instatic before 0.0.21 Authorization Bypass via MCP Content Read Tools

Medium 6.5

In plain English

A medium-severity missing authorization in Instatic from CoreBunch. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 24% of all known vulnerabilities).

Severity (CVSS 3.1)6.5Medium

Exploit odds (30 days)0.3%top 76.2% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

Instatic before 0.0.21 contains a missing authorization vulnerability in its AI/MCP content read tools that allows low-privileged authenticated users with ai.chat and content.edit.own capabilities to access data rows belonging to other users by calling content_get_document and content_list_documents without the object-level authorization checks enforced by the normal HTTP API. Attackers can use the MCP interface to retrieve private or unpublished draft content and enumerate rows from the posts system table, resulting in cross-user data disclosure.

Affected products (as reported)

Vendor	Product	Versions
CoreBunch	Instatic	0.0.12 – before 0.0.21

Weakness: CWE-862 · Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

References

Vendor Advisory vendor-advisory, technical-description
Vendor Patch patch, issue-tracking
VulnCheck Advisory: Instatic before 0.0.21 Authorization Bypass via MCP Content Read Tools third-party-advisory