CVE-2017-20239

Vulnerability

Description

MDwiki, a client-side wiki system built entirely on HTML5 and JavaScript, suffers from a cross-site scripting (XSS) vulnerability due to improper sanitization of the location hash parameter. The application reads the hash fragment from the URL (e.g., #!) and directly assigns it to a.md.mainHref after URL decoding, without any validation or escaping [1][2]. This raw input is subsequently used to fetch content via an AJAX request and is later rendered through the marked library, which interprets the payload as Markdown and raw HTML, leading to execution of injected scripts [1].

Exploitation

An attacker can exploit this vulnerability by crafting a malicious URL containing a JavaScript payload in the hash fragment, such as #!. The victim must click on the crafted link, which triggers the vulnerable code path. The payload is parsed, fetched, and rendered in the context of the MDwiki page, executing the attacker's script in the victim's browser [1]. No authentication is required beyond the victim visiting the link, and the attack can be performed remotely over the network [2].

Impact

Successful exploitation allows the attacker to execute arbitrary JavaScript in the context of the victim's session against the MDwiki origin. This can lead to session hijacking, data theft, defacement, or further attacks against the user's browser [2]. The CVSS v3.1 score is 6.1 (Medium), reflecting the need for user interaction and low impact to confidentiality and integrity [2].

Mitigation

As of the disclosure date, no official patch has been released for MDwiki. The project may be unmaintained. Administrators should consider implementing input sanitization for the hash parameter or upgrading to an alternative wiki solution. The vulnerability has been publicly documented in exploit databases and advisory platforms [1][2].