CVE-2021-43856 Stored XSS in non-image uploads in Requarks/wiki

High 8.2 Published 27 Dec 2021 Updated 4 Aug 2024

A malicious user can upload files that execute JavaScript when viewed inline, allowing stored XSS attacks against other users.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: A user has to click or open something
Fix: None listed

What is CVE-2021-43856?

CVE-2021-43856 is a high-severity cross-site scripting vulnerability in Requarks wiki, published on 27 Dec 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

Official description

Wiki.js is a wiki app built on Node.js. Wiki.js 2.5.263 and earlier is vulnerable to stored cross-site scripting through non-image file uploads for file types that can be viewed directly inline in the browser. By creating a malicious file which can execute inline JS when viewed in the browser (e.g. XML files), a malicious Wiki.js user may stage a stored cross-site scripting attack. This allows the attacker to execute malicious JavaScript when the file is viewed directly by other users. The file must be opened directly by the user and will not trigger directly in a normal Wiki.js page. A patch in version 2.5.264 fixes this vulnerability by adding an optional (enabled by default) force download flag to all non-image file types, preventing the file from being viewed inline in the browser. As a workaround, disable file upload for all non-trusted users. --- Thanks to @Haxatron for reporting this vulnerability. Initially reported via https://huntr.dev/bounties/266bff09-00d9-43ca-a4bb-bb540642811f/

Weakness: CWE-79

Which versions are affected by CVE-2021-43856?

It affects 1 product.

Products include Requarks Wiki.js.

How do I fix CVE-2021-43856?

No fix has been published for CVE-2021-43856 yet. Limit exposure of the affected software until one is available.

Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.

Is CVE-2021-43856 being exploited?

There is no known exploitation of CVE-2021-43856 in the wild and no public exploit code.

Sources

Also known as GHSA-rhpf-929m-7fm2.