CVE-2021-24153

Yoast SEO <= 3.4.0 - Authenticated Stored Cross-Site Scripting

2016-08-02 00:00
Hammad Shamsi

Strategic Overview

Status
Patched in 3.4.1
Affected Plugin
Yoast SEO – Advanced SEO with real-time guidance and built-in AI
Affected Version
< 3.4.1
CVSS
5.4Medium
Weakness type
CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CVE
CVE-2021-24153
View all Yoast SEO – Advanced SEO with real-time guidance and built-in AI vulnerabilities

At a glance

CVE-2021-24153 is a medium-severity Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in the Yoast SEO WordPress plugin, affecting versions < 3.4.1. It carries a CVSS score of 5.4 (reachable over the network; low attack complexity). Exploitation requires an authenticated account. The issue is fixed in version 3.4.1; sites on affected versions should update now. Disclosed August 2016, reported by Hammad Shamsi.

Vulnerability Overview

A Stored Cross-Site Scripting vulnerability was discovered in the Yoast SEO WordPress plugin before 3.4.1, which had built-in blacklist filters which were blacklisting parentheses as well as several functions such as alert, but bypasses were found.

Technical Analysis

The vector marks this flaw as remotely reachable over the network, with low attack complexity — no special timing or configuration is needed.

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

Reaching this weakness in Yoast SEO < 3.4.1 takes any authenticated account. 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 3.4.1: builds < 3.4.1 are affected, anything from 3.4.1 onward is not.

Remediation

Update to version 3.4.1, or a newer patched version

How does WordSec protect against this?

The attempt arrives as an ordinary request to Yoast SEO: WordSec's web application firewall inspects request payloads before WordPress loads them. None of that substitutes for the fix: Yoast SEO 3.4.1 closes this, and updating the plugin is the step that ends it.

  • Firewall
  • Alerts

External References

https://www.cve.org/CVERecord?id=CVE-2021-24153https://www.wordfence.com/threat-intel/vulnerabilities/id/0cde6b5b-f760-467b-940f-06a1f983ddc4https://nvd.nist.gov/vuln/detail/CVE-2021-24153

Related records

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