CVE-2021-24927

My Calendar <= 3.2.17 - Subscriber+ Reflected Cross-Site Scripting

2021-11-01 00:00
Krzysztof Zając

Strategic Overview

Status
Patched in 3.2.18
Affected Version
<= 3.2.17
CVSS
5.4Medium
Weakness type
CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CVE
CVE-2021-24927
View all My Calendar – Accessible Event Manager vulnerabilities

At a glance

CVE-2021-24927 is a medium-severity Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in the My Calendar WordPress plugin, affecting versions <= 3.2.17. It carries a CVSS score of 5.4 (reachable over the network; low attack complexity). The issue is fixed in version 3.2.18; sites on affected versions should update now. Disclosed November 2021, reported by Krzysztof Zając.

Vulnerability Overview

The My Calendar WordPress plugin before 3.2.18 does not sanitise and escape the callback parameter of the mc_post_lookup AJAX action (available to any authenticated user) before outputting it back in the response, leading to a Reflected Cross-Site Scripting issue

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 My Calendar <= 3.2.17 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 My Calendar the fix is 3.2.18: builds <= 3.2.17 are affected, anything from 3.2.18 onward is not.

Remediation

Update to version 3.2.18, or a newer patched version

How does WordSec protect against this?

The attempt arrives as an ordinary request to My Calendar: WordSec's web application firewall inspects request payloads before WordPress loads them. None of that substitutes for the fix: My Calendar 3.2.18 closes this, and updating the plugin is the step that ends it.

  • Firewall
  • Alerts

External References

Related records

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