CVE-2026-121458
Instatic before 0.0.21 Authorization Bypass via MCP Content Read Tools
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 Attackers can use the MCP interface to retrieve private or unpublished draft content and enumerate rows from the posts system table, resulting in cross-user data disclosure.
Fixes and workarounds
Fix
The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches.
Source: CNA: VulnCheckAffected products and versions
| Product | Versions | Authority |
|---|---|---|
| Instatic CoreBunch CoreBunch/Instatic
github |
≥ 0.0.12; < 0.0.21 (affected, semver)
Other versions: unaffected |
CNA: VulnCheck |
Version ranges are source assertions. Check the vendor advisory and your installed configuration before determining exposure.
CVSS assessments
| Version / score | Vector | Authority |
|---|---|---|
| 4.0 / 7.1 high |
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N | CNA: VulnCheck |
| 3.1 / 6.5 medium |
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N | CNA: VulnCheck |
Exploit evidence
No exploit evidence in collected sources. This is not proof of no exploitation.
References
- https://github.com/CoreBunch/Instatic/security/advisories/GHSA-x5cc-8486-8qqxCNA: VulnCheck · vendor-advisory, technical-description
- https://github.com/CoreBunch/Instatic/releases/tag/v0.0.21CNA: VulnCheck · patch, issue-tracking
- https://www.vulncheck.com/advisories/instatic-before-authorization-bypass-via-mcp-content-read-toolsCNA: VulnCheck · third-party-advisory
For agents and automation
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Endpoints and access details
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