WordPress 3.7–4.9.1 MediaElement Cross Site Scripting

A cross-site scripting vulnerability exists in the Flash fallback files provided by MediaElement, a library included in WordPress Core. This vulnerability is present in versions 3.7–4.9.1. An attacker is able to inject JavaScript payloads via crafted HTTP requests, resulting in reflective XSS. This vulnerability is exploitable via two vulnerable files, plupload.flash.swf and flashmediaelement.swf. Authentication is not required for successful exploitation of this vulnerability.

Exploitation

Stages

1. The attacker sends an HTTP GET request to MediaElement’s flash fallback files that contains an escaped XSS payload.
2. The injected payload is reflected by the targeted parameter resulting in reflective XSS.

Prerequisites

The WordPress Core versions 3.7–4.9.1 can be accessed directly by unauthenticated attackers.

Alert Logic Coverage

Alert Logic® has evaluated its customer base for exposure to the exploit and has developed signatures for mitigating the threat depending on the security service in place.

The Network-Based Intrusion Detection System (IDS) has been updated with the new signatures for this exploit when detected via Alert Logic Threat Manager™. If this signature is detected, an incident is generated in the Alert Logic console.

Recommendations for Mitigation

Upgrade to a non-vulnerable version to mitigate this vulnerability.