CVE-2021-21259 Stored XSS in slide mode

What is CVE-2021-21259?

CVE-2021-21259 is a high-severity cross-site scripting vulnerability in hedgedoc, published on 22 Jan 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

HedgeDoc is open source software which lets you create real-time collaborative markdown notes. In HedgeDoc before version 1.7.2, an attacker can inject arbitrary JavaScript into a HedgeDoc note, which is executed when the note is viewed in slide mode. Depending on the configuration of the instance, the attacker may not need authentication to create or edit notes. The problem is patched in HedgeDoc 1.7.2. As a workaround, disallow loading JavaScript from 3rd party sites using the `Content-Security-Policy` header. Note that this will break some embedded content.

Weakness: CWE-79

Which versions are affected by CVE-2021-21259?

It affects 1 product.

Products include Hedgedoc Hedgedoc.

How do I fix CVE-2021-21259?

No fix has been published for CVE-2021-21259 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-2021-21259 being exploited?

There is no known exploitation of CVE-2021-21259 in the wild and no public exploit code.

Other vulnerabilities in hedgedoc

• CVE-2021-29475 PDF export allows arbitrary file reads Critical 10.0
• CVE-2020-26287 Stored XSS in mermaid diagrams High 8.7
• CVE-2021-39175 XSS vector in slide mode speaker-view High 8.1
• CVE-2021-29503 Improper Neutralization of Script-Related HTML Tags in Notes High 8.1
• CVE-2020-26286 Arbitary file upload High 7.5

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-44w9-vm8p-3cxw.