CVE-2021-29474 Relative Path Traversal Attack on note creation
An attacker can read arbitrary markdown files from the server filesystem via relative path traversal in HedgeDoc.
- 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-2021-29474?
CVE-2021-29474 is a medium-severity path traversal vulnerability in hedgedoc, published on 26 Apr 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 (formerly known as CodiMD) is an open-source collaborative markdown editor. An attacker can read arbitrary `.md` files from the server's filesystem due to an improper input validation, which results in the ability to perform a relative path traversal. To verify if you are affected, you can try to open the following URL: `http://localhost:3000/..%2F..%2FREADME#` (replace `http://localhost:3000` with your instance's base-URL e.g. `https://demo.hedgedoc.org/..%2F..%2FREADME#`). If you see a README page being rendered, you run an affected version. The attack works due the fact that the internal router passes the url-encoded alias to the `noteController.showNote`-function. This function passes the input directly to findNote() utility function, that will pass it on the the parseNoteId()-function, that tries to make sense out of the noteId/alias and check if a note already exists and if so, if a corresponding file on disk was updated. If no note exists the note creation-function is called, which pass this unvalidated alias, with a `.md` appended, into a path.join()-function which is read from the filesystem in the follow up routine and provides the pre-filled content of the new note. This allows an attacker to not only read arbitrary `.md` files from the filesystem, but also observes changes to them. The usefulness of this attack can be considered limited, since mainly markdown files are use the file-ending `.md` and all markdown files contained in the hedgedoc project, like the README, are public anyway. If other protections such as a chroot or container or proper file permissions are in place, this attack's usefulness is rather limited. On a reverse-proxy level one can force a URL-decode, which will prevent this attack because the router will not accept such a path.
Which versions are affected by CVE-2021-29474?
It affects 1 product.
Products include Hedgedoc Hedgedoc.
How do I fix CVE-2021-29474?
No fix has been published for CVE-2021-29474 yet. Limit exposure of the affected software until one is available.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2021-29474 being exploited?
There is no known exploitation of CVE-2021-29474 in the wild and no public exploit code.
Other vulnerabilities in hedgedoc
Sources
Also known as GHSA-p528-555r-pf87.