Cyber Resilience

CVE-2026-66399

Public PoC
Published
27 July 2026
Modified
28 July 2026
CVSS Score v4 8.5
Click a component to see what it means
Raw vectorCVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/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 0.0023 14th percentile
Risk Priority 29 floored blend · peak EPSS

Summary

CVE-2026-66399 is a high-severity Improper Privilege Management (CWE-269) vulnerability. Its CVSS base score is 8.5 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Abuse Elevation Control Mechanism (T1548); ranked at the 14th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to AC-2 (Account Management) and AC-24 (Access Control Decisions) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A06:2025 Insecure Design

EU & UK References

Vulnerability Data

phpMyFAQ before 4.1.6 contains a privilege escalation vulnerability in GroupController::updateMembers() that allows administrators with only group-management permissions to join privileged groups without verification of required rights. Attackers can add themselves to pre-existing groups holding user-management rights and immediately inherit those…

more

permissions to modify or delete user accounts.

CWE(s)
CWE-269

Related Threats

MITRE ATT&CK Enterprise Techniques

T1548 Abuse Elevation Control Mechanism Privilege Escalation
Adversaries may circumvent mechanisms designed to control privilege elevation to gain higher-level permissions.
attack.mitre.org →
T1134 Access Token Manipulation Stealth
Adversaries may modify access tokens to operate under a different user or system security context to perform actions and bypass access controls.
attack.mitre.org →
T1548.001 Setuid and Setgid Privilege Escalation
An adversary may abuse configurations where an application has the setuid or setgid bits set in order to get code running in a different (and possibly more privileged) user’s context.
attack.mitre.org →
T1548.003 Sudo and Sudo Caching Privilege Escalation
Adversaries may perform sudo caching and/or use the sudoers file to elevate privileges.
attack.mitre.org →
T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1078 Valid Accounts Stealth
Adversaries may obtain and abuse credentials of existing accounts as a means of gaining Initial Access, Persistence, Privilege Escalation, or Defense Evasion.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2019-1405Shared CWE-269
CVE-2024-41949Shared CWE-269
CVE-2023-41957Shared CWE-269
CVE-2023-4607Shared CWE-269
CVE-2023-37925Shared CWE-269
CVE-2023-41808Shared CWE-269
CVE-2024-0439Shared CWE-269
CVE-2024-37484Shared CWE-269
CVE-2023-23430Shared CWE-269
CVE-2026-60248Shared CWE-269

Affected Assets

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 5 hardening rules · 5 OS baselines
Validate
Prove the fix (OWASP ASVS)

—

Mitigating Controls (NIST 800-53 r5) AI

AC-2 Account Management good match

Account management directly governs assignment and tracking of privileges so proper implementation stops the weakness from being introduced.

AC-24 Access Control Decisions good match

Requiring explicit access-control decisions ensures privileges are evaluated rather than assumed or omitted.

AC-3 Access Enforcement good match

Access enforcement applies the correct privilege checks at every request, structurally preventing unintended spheres of control.

AC-5 Separation of Duties good match

Separation of duties constrains how privileges may be assigned, reducing the chance of overly broad actor control.

AC-6 Least Privilege good match

Least privilege is the direct countermeasure to improper privilege management; implementing it eliminates the root cause.

AC-16 Security and Privacy Attributes partial match

Binding security attributes to subjects/objects supplies the mechanism needed to track and enforce privileges correctly.

Mitigating Controls (NIST CSF 2.0) AI

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

PR.AA-05 mostly match
prevents

PR.AA-05 enforces least privilege/SoD and periodic reviews that directly remove most privilege-assignment defects, yet CWE-269 also covers escalation paths and role design outside a single access-management control.

PR.AA-01 partial match
prevents

PR.AA-01 supplies credential/identity lifecycle support that can reduce some privilege-assignment errors but does not itself assign, modify, or check privileges, leaving most of CWE-269's risk unaddressed.

PR.PS-01 partial match
prevents

Config baselines and default reviews can enforce some privilege-related settings (one facet) but do not address code-level assignment/tracking logic that defines CWE-269.

PR.PS-05 partial match
prevents

PR.PS-05 can partially limit exploitability of some privilege issues via execution restrictions, but does not address the core design/implementation flaws of CWE-269 at all.

PR.DS-10 none match
prevents

PR.DS-10 protects data-in-use without touching privilege assignment/tracking, so it neither prevents CWE-269 nor removes more than one narrow facet of its risk.

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.

A.5.18 Access rights mostly match
prevents

Requiring owner approval, segregation of duties, and periodic reviews prevents the assignment of excessive or unnecessary privileges to users or processes.

A.8.2 Privileged access rights mostly match
prevents

Enforcing minimum-necessary privileges, temporary grants, and separation of administrative versus normal identities prevents the over-assignment of rights that CWE-269 describes.

A.8.3 Information access restriction mostly match
prevents

Dynamic techniques that grant the minimum necessary rights for a given time window and revoke them afterward reduce the window in which excessive or unnecessary privileges can be exploited.

A.5.15 Access control partial match
prevents

Explicit restrictions on privileged access and segregation of duties limit the scope of privileges that can be assigned, reducing the chance that excessive or unnecessary privileges are granted to entities.

A.5.2 Information security roles and responsibilities partial match
prevents

Defining and communicating authorization levels for each role limits the assignment of excessive or unnecessary privileges.

A.5.3 Segregation of duties partial match
mitigates

Separating duties such as developing software from administering production systems prevents any one person from accumulating excessive privileges that would constitute improper privilege management.

References