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TI-2026-84250 Aliases CVE-2026-121458GHSA-wq53-554h-vq3f

Instatic MCP read tools bypass authorization, exposing other users' data

Priority LOW 31CWE-862Published · Updated

Key facts

Attack vector
Network
Privileges required
Low
User interaction
None
Attack complexity
Low
Attack requirements
None
Impact type
Security bypass
Confidentiality · integrity · availability
High · None · None
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-862.

Summary

Instatic from 0.0.12 before 0.0.21 is affected by a missing authorization flaw (CWE-862) in its AI/MCP content read tools. An authenticated user with low privileges, including the ai.chat and content.edit.own capabilities, can call content_get_document and content_list_documents to read rows owned by other users, bypassing the object-level checks of the normal HTTP API. This exposes private and unpublished draft content from the posts table to other users.

Written with Claude Haiku 5.5 from the sources below · 2026-11-03

Description from the CNA

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 Attackers can use the MCP interface to retrieve private or unpublished draft content and enumerate rows from the posts system table, resulting in cross-user data disclosure.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00309 23rd percentileScored 2026-11-07
Fix Fixed Instatic (CoreBunch): 0.0.21

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
CoreBunchInstatic0.0.12 to before 0.0.210.0.21Patch availableCNA
  • Instatic VendorCoreBunch Affected 0.0.12 to before 0.0.21 Fixed in 0.0.21 Patch available CNA

Remediation

Upgrade Instatic to version 0.0.21 or later, which fixes the flaw in CoreBunch Instatic.

Written with Claude Haiku 5.5 from the sources below · 2026-11-03

  • Fix · CNA Instatic (CoreBunch) Fixed in 0.0.21

Timeline

  1. 2026-11-03 Threatist record created from CVE-2026-121458
  2. 2026-11-03 Alias added: GHSA-wq53-554h-vq3f
  3. 2026-11-03 CISA SSVC decision points changed
  4. 2026-11-03 Priority changed: MEDIUM → LOW

References

Patch 1

Advisory 1

  • TI-2026-50844 Instatic - Cache Poisoning via Unauthenticated Server Island Endpoint CVSS 3.1MEDIUM 6.1

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences