CVE-2021-20866

Advanced Custom Fields <= 5.10 - Missing Authorization to Information Disclosure

2021-12-02 00:00

Strategic Overview

Status: Patched in 5.11
Affected Plugin: Advanced Custom Fields Pro
Affected Version: < 5.11
CVSS: 6.5Medium
Weakness type: CWE-862 · Missing Authorization
CVE: CVE-2021-20866

View all Advanced Custom Fields Pro vulnerabilities

At a glance

CVE-2021-20866 is a medium-severity Missing Authorization vulnerability in the Advanced Custom Fields Pro WordPress plugin, affecting versions < 5.11. It carries a CVSS score of 6.5 (reachable over the network; low attack complexity; high confidentiality impact). The root cause is a missing authorization check on a reachable function. The issue is fixed in version 5.11; sites on affected versions should update now. Disclosed December 2021, reported by Keitaro Yamazaki.

Vulnerability Overview

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.

Technical Analysis

The vector marks this flaw as remotely reachable over the network, with low attack complexity — no special timing or configuration is needed, and no interaction from a victim user. A successful exploit has high impact on confidentiality.

CWE-862: Missing Authorization

Reaching this weakness in Advanced Custom Fields Pro < 5.11 takes a caller who can reach the endpoint. A missing authorization check means a function is reachable by anyone who can reach the endpoint, because the code never asks whether the caller is allowed to perform the action.

Any user who can reach the endpoint gets to run an action reserved for higher-privileged roles, from reading protected data to changing settings or content. For Advanced Custom Fields Pro the fix is 5.11: builds < 5.11 are affected, anything from 5.11 onward is not.

Remediation

Update to version 5.11, or a newer patched version

How does WordSec protect against this?

Because it turns on account access, WordSec's login security is the relevant layer: role-based two-factor, captcha and brute-force limits raise the cost of getting the account this needs. None of that substitutes for the fix: Advanced Custom Fields Pro 5.11 closes this, and updating the plugin is the step that ends it.

Login Security
Alerts

External References

https://www.cve.org/CVERecord?id=CVE-2021-20866 https://www.wordfence.com/threat-intel/vulnerabilities/id/f1eb0852-00ef-489a-aa39-7d8603249deb https://nvd.nist.gov/vuln/detail/CVE-2021-20866

Related records

Same weakness class

Other vulnerabilities in Advanced Custom Fields Pro

CVSS Vector

6.5

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N

Base

Attack VectorNetwork
Attack ComplexityLow
Privileges RequiredLow
User InteractionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityNone
AvailabilityNone

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