W3 Total Cache <= 0.9.4.1 - Cross-Site Scripting via request_id

2016-07-29 00:00
Sipke Mellema

Strategic Overview

Status
Patched in 0.9.5
Affected Plugin
W3 Total Cache
Affected Version
<= 0.9.4.1
CVSS
6.1Medium
Weakness type
CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CVE
CVE pending
View all W3 Total Cache vulnerabilities

At a glance

This record tracks a medium-severity Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in the W3 Total Cache WordPress plugin, affecting versions <= 0.9.4.1. It carries a CVSS score of 6.1 (reachable over the network; low attack complexity). Exploitation requires no authentication. The issue is fixed in version 0.9.5; sites on affected versions should update now. Disclosed July 2016, reported by Sipke Mellema.

Vulnerability Overview

The W3 Total Cache plugin plugin for WordPress is vulnerable to Cross-Site Scripting via the 'request_id' parameter in versions up to, and including, 0.9.4.1 due to insufficient input sanitization and output escaping. This makes it possible for attackers to inject arbitrary web scripts that execute in a victim's browser.

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 privileges on the target site.

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

W3 Total Cache <= 0.9.4.1 carries this weakness at request_id, and reaching it takes a caller who can reach the endpoint. 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 W3 Total Cache the fix is 0.9.5: builds <= 0.9.4.1 are affected, anything from 0.9.5 onward is not.

Remediation

Update to version 0.9.5, or a newer patched version

How does WordSec protect against this?

The attempt arrives as an ordinary request to W3 Total Cache: WordSec's web application firewall inspects request payloads before WordPress loads them. None of that substitutes for the fix: W3 Total Cache 0.9.5 closes this, and updating the plugin is the step that ends it.

  • Firewall
  • Alerts

External References

https://www.wordfence.com/threat-intel/vulnerabilities/id/3b8282a2-8265-4fa0-b137-6272b9e44fc3

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