Security Resilience

CVE-2026-66012

Access Control

Public PoCAccess Control
Published
25 July 2026
Modified
17 September 2026
CVSS Score v4 10.0
Click a component to see what it means
Raw vectorCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS Score 0.0076 54th percentile
Risk Priority 48 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2026-66012 is a critical-severity Missing Authorization (CWE-862) vulnerability. Its CVSS base score is 10.0 (Critical).

Operationally, ranked in the top 46% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

This vulnerability is AI-related — categorised as AI Agent Protocols and Integrations; in the Protocol-Specific Risks risk domain.

The strongest mitigations our analysis identified map to AC-24 (Access Control Decisions) and AC-25 (Reference Monitor) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

EU & UK References

Vulnerability Data

SiYuan before v3.7.2 contains a missing authorization vulnerability in the POST /mcp kernel endpoint, which is gated only by a general auth check (model.CheckAuth) with no admin-role or read-only enforcement. This exposes 31 MCP tools, including a file tool with…

more

list/read/write/delete/rename/copy actions across the entire workspace. When the Publish server is enabled in anonymous mode (Conf.Publish.Enable=true and Conf.Publish.Auth.Enable=false), the Publish reverse proxy attaches an anonymous RoleReader JWT to proxied requests, allowing a remote unauthenticated attacker to reach /mcp. The attacker can read conf/conf.json to extract accessAuthCode, api.token, and cookieKey in plaintext, write arbitrary files in the workspace, and plant a plugin into data/plugins/ that executes with nodeIntegration:true and no contextIsolation on the next desktop launch, leading to administrator takeover.

CWE(s)

AI Security AnalysisAI

AI Category
AI Agent Protocols and Integrations
Risk Domain
Protocol-Specific Risks
OWASP Top 10 for LLMs 2025
None mapped
Classification Reason
Matched keywords: mcp, mcp, mcp

Related Threats

CVEs Like This One

CVE-2025-64132Shared CWE-862
CVE-2024-32081Shared CWE-862
CVE-2025-24633Shared CWE-862
CVE-2024-38721Shared CWE-862
CVE-2023-21133Shared CWE-862
CVE-2025-53291Shared CWE-862
CVE-2024-56066Shared CWE-862
CVE-2023-1337Shared CWE-862
CVE-2025-23190Shared CWE-862
CVE-2023-46195Shared CWE-862

Affected Assets

Mitigating Controls

Mitigating Controls (NIST 800-53 r5) AI

AC-3 directly requires enforcement of authorization decisions on every access request, structurally eliminating missing authorization checks.

AC-24 mandates that access control decisions are applied to each request, preventing bypass of authorization logic.

AC-25 requires a tamperproof, always-invoked reference monitor that ensures authorization checks cannot be omitted.

AC-6 reduces the set of actions reachable without proper authorization, limiting blast radius of missing checks.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

blocks

Requiring formal authorization of every access request before rights are granted ensures that checks for required permissions are performed, preventing missing authorization checks from being introduced.

blocks

A.5.18's provisioning, review, revocation and activation steps (incl. owner approval, SoD, timely removal on role/termination change) directly stop exploitation of missing authorization checks by ensuring no actor receives or retains rights to resources they should not access; the bounded remainder is that it cannot stop missing-authorization defects inside the enforcement mechanism itself once rights have been granted (e.g. flawed code that ignores the rights table).

finds

By requiring competent outsiders to verify that every function enforces the need-to-know principle, the control lowers the likelihood that missing authorization checks persist undetected.

blocks

A.5.8 integrates risk assessment, requirements elicitation and governance into the project lifecycle so that authorization needs can be identified and specified; it does not itself perform or enforce authorization checks, so the missing-authorization weakness can still be present and exploitable.

blocks

Security checkpoints and explicit authorization requirements in the design phase ensure that every sensitive function is paired with an access-control check, reducing missing-authorization defects.

blocks

A.8.27 mandates security-by-design principles (least privilege, default deny, security architecture integration, zero-trust never-trust/always-verify, dynamic access control) plus design reviews that directly specify and enforce authorization checks before access; this stops most missing-authorization cases from being exploitable, with a bounded remainder in non-architectural or legacy components where the principles were documented but not fully applied.

Hardening callouts derived

DISA STIG baselines are authored against specific weaknesses. Where this CVE cites a broad weakness class, the mapping is not asserted at that abstraction (owner ruling, 2026-09-25: grade only at Base and below), so no rule is shown here rather than a rule shown against the wrong grain.

  • No fine-grained STIG row for CWE-862, a class-level weakness, and none of its children carries one either.

References