CVE-2021-36872

WordPress Popular Posts <= 5.3.3 - Authenticated (Admin+) Stored Cross-Site Scripting

2021-07-04 20:59

Strategic Overview

Status: Patched in 5.3.4
Affected Plugin: WP Popular Posts
Affected Version: <= 5.3.3
CVSS: 5.5Medium
Weakness type: CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CVE: CVE-2021-36872

At a glance

CVE-2021-36872 is a medium-severity Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in the WP Popular Posts WordPress plugin, affecting versions <= 5.3.3. It carries a CVSS score of 5.5 (reachable over the network; low attack complexity). Exploitation requires an authenticated account at Admin level or above. The issue is fixed in version 5.3.4; sites on affected versions should update now. Disclosed July 2021, reported by R3N0.

Vulnerability Overview

Authenticated Persistent Cross-Site Scripting (XSS) vulnerability in WordPress Popular Posts plugin (versions <= 5.3.3). Vulnerable at &widget-wpp[2][post_type].

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.

CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Reaching this weakness in WP Popular Posts <= 5.3.3 takes an account at Admin level or above. Cross-site scripting happens when input from a request is written into a page without being escaped for the context it lands in, so the browser parses attacker-supplied text as markup or script.

Injected script runs with the privileges of whoever views the affected page, which is how these flaws turn into administrator session theft, silent account creation or persistent backdoors in page content. For WP Popular Posts the fix is 5.3.4: builds <= 5.3.3 are affected, anything from 5.3.4 onward is not.

Remediation

Update to version 5.3.4, or a newer patched version

How does WordSec protect against this?

An attacker needs Admin access first, so the firewall sees the attempt as traffic from a logged-in account: WordSec's web application firewall inspects request payloads before WordPress loads them. None of that substitutes for the fix: WP Popular Posts 5.3.4 closes this, and updating the plugin is the step that ends it.

Firewall
Alerts

External References

https://www.cve.org/CVERecord?id=CVE-2021-36872 https://www.wordfence.com/threat-intel/vulnerabilities/id/e9012824-7221-4b93-a5fb-65caf7994e92 https://nvd.nist.gov/vuln/detail/CVE-2021-36872

Related records

Same weakness class

CVSS Vector

5.5

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

Base

Attack VectorNetwork
Attack ComplexityLow
Privileges RequiredHigh
User InteractionNone
ScopeChanged
ConfidentialityLow
IntegrityLow
AvailabilityNone

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