What is the CVSS score of CVE-2021-20866?

CVE-2021-20866 has a CVSS 3.1 base score of 6.5 (Medium). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N. EPSS exploitation probability: 1.7%.

Advanced Custom Fields CVE-2021-20866

MEDIUM

Missing Authorization (CWE-862)

2021-12-13 vultures@jpcert.or.jp

WordPress Authentication Bypass Advanced Custom Fields Wordpress Plugin Advancedcustomfields

6.5

CVSS 3.1 · NVD

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Vulnerability Assessment

Weakness	CWE CWE-862 OWASP Top 10:2025 A01:2025 - Broken Access Control ASVS 5.0 V8 - Authorization Authorization checks on every request MITRE ATT&CK 1 technique across 1 tactic: Privilege Escalation The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. Sign in to read
Impact	CVSS score of 6.5 (MEDIUM). Attack characteristics: network attack vector, low complexity, low privileges required, no user interaction not required.
Exploit ScenarioDerived	A remote attacker could access resources or perform actions without proper authorization checks by sending crafted requests to the affected application.

This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).

No patch listed yet 1.7% exploitation probability (EPSS)

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AnalysisAI

Advanced Custom Fields versions prior to 5.11 and Advanced Custom Fields Pro versions prior to 5.11 contain a missing authorization vulnerability in obtaining the user list which may allow a user to. Rated medium severity (CVSS 6.5), this vulnerability is remotely exploitable, low attack complexity. No vendor patch available.

RemediationAI

No vendor patch is available at time of analysis. Monitor vendor advisories for updates. Implement role-based access control, validate authorization on every request server-side, apply principle of least privilege.

Affects your stack

Find out whether the stacks and servers you run are on an affected version.

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

This vulnerability is classified as Missing Authorization (CWE-862), which allows attackers to access resources or perform actions without proper authorization checks. Advanced Custom Fields versions prior to 5.11 and Advanced Custom Fields Pro versions prior to 5.11 contain a missing authorization vulnerability in obtaining the user list which may allow a user to obtain the unauthorized information via unspecified vectors. Affected products include: Advancedcustomfields Advanced Custom Fields. Version information: prior to 5.11.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 6.5 MEDIUM

AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

None

Availability

None

DescriptionNVD

Advanced Custom Fields versions prior to 5.11 and Advanced Custom Fields Pro versions prior to 5.11 contain a missing authorization vulnerability in obtaining the user list which may allow a user to obtain the unauthorized information via unspecified vectors.

Threat Intelligence Overview

EPSS Score

1.7%

Top 26% exploitable

Data Quality

2 sources

Confidence: Low

NVD

CVE.org

EPSS

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity MEDIUM

CISA KEV No

Public POC No

EPSS 1.7%

Patch available No

Active threat No

Deciding rule

MEDIUM severity (CVSS 4.0-6.9)

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Scheduled

Exploitation· derived

None

System Exposure· derived

Open

Automatable· derived

Human Impact· derived

Medium

Priority Score

Low Medium High Critical

KEV: 0

EPSS: +2

CVSS: +32

PoC: 0

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Authentication Bypass CRITICAL

Authentication bypass attacks exploit flaws in the verification mechanisms that control access to systems and applications.

Affected Products (CPE)NVD

cpe:2.3:a:advancedcustomfields:advanced_custom_fields:*:*:*:*:*:wordpress:*:*

cpe:2.3:a:advancedcustomfields:advanced_custom_fields:*:*:*:*:pro:wordpress:*:*

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The Advanced Custom Fields Pro WordPress plugin before 5.9.1 did not properly escape the generated update URL when outpu

CVE-2026-8809 CRITICAL Act Now

9.8 May 28

Unauthenticated privilege escalation in the Advanced Custom Fields: Extended (ACFE) WordPress plugin through version 0.9

CVE-2026-48906 CRITICAL Act Now

9.3 May 27

Arbitrary file deletion in the Novarain/Tassos Framework system plugin (plg_system_nrframework) and the suite of Tassos.

CVE-2026-94263 MEDIUM This Month POC

4.8 Oct 23

Improper shortcode handling in the Advanced Custom Fields: Extended and ACF Extended PRO WordPress plugins (versions 0.9

CVE-2021-20865 HIGH This Week

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Advanced Custom Fields versions prior to 5.11 and Advanced Custom Fields Pro versions prior to 5.11 contain a missing au

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CVE-2024-0012 CRITICAL POC

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References

Advisories & patches

ADVISORY https://www.advancedcustomfields.com/ REF https://jvn.jp/en/jp/JVN09136401/index.html REF https://wordpress.org/plugins/advanced-custom-fields/

Search Externally

GitHub PoC

Exploit-DB PacketStorm Snyk Rapid7 Nuclei Templates Trickest PoC

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