Yoast SEO <= 20.2 - Authenticated (Contributor+) Stored Cross-Site Scripting

2023-03-02 00:00
Leonidas Milosis

Strategic Overview

Status
Patched in 20.2.1
Affected Plugin
Yoast SEO – Advanced SEO with real-time guidance and built-in AI
Affected Version
<= 20.2
CVSS
6.4Medium
Weakness type
CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CVE
CVE pending
View all Yoast SEO – Advanced SEO with real-time guidance and built-in AI vulnerabilities

At a glance

This record tracks a medium-severity Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in the Yoast SEO WordPress plugin, affecting versions <= 20.2. It carries a CVSS score of 6.4 (reachable over the network; low attack complexity). Exploitation requires an authenticated account at Contributor level or above. The issue is fixed in version 20.2.1; sites on affected versions should update now. Disclosed March 2023, reported by Leonidas Milosis.

Vulnerability Overview

The Yoast SEO plugin for WordPress is vulnerable to DOM-based Cross-Site Scripting via individual post SEO details in versions up to, and including, 20.2 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers with contributor-level requirements and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.

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 Yoast SEO <= 20.2 takes an account at Contributor 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 Yoast SEO the fix is 20.2.1: builds <= 20.2 are affected, anything from 20.2.1 onward is not.

Remediation

Update to version 20.2.1, or a newer patched version

How does WordSec protect against this?

An attacker needs Contributor 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: Yoast SEO 20.2.1 closes this, and updating the plugin is the step that ends it.

  • Firewall
  • Alerts

External References

https://www.wordfence.com/threat-intel/vulnerabilities/id/c0e58807-bccc-469f-82c3-a4bbf088a626

Related records

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