CVE-2021-29474

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.

• CVE ID
• CVE-2021-29474

• Assigner
• security-advisories@github.com

• Vulnerability Status
• Analyzed

• Published Version
• 2021-04-26T22:15:08

• Last Modified Date
• 2022-10-24T18:21:13

• Version
• 2.0

• Vector String
• AV:N/AC:L/Au:N/C:P/I:N/A:N

• Access Vector
• NETWORK

• Access Compatibility
• LOW

• Authentication
• NONE

• Confidentiality Impact
• PARTIAL

• Integrity Impact
• NONE

• Availability Impact
• NONE

• Base Score
• 5

• Severity
• MEDIUM

• Exploitability Score
• 10

• Impact Score
• 2.9

• Version
• 3.1

• Vector String
• CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N

• Attack Vector
• NETWORK

• Attack Compatibility
• LOW

• Privileges Required
• NONE

• User Interaction
• NONE

• Scope
• CHANGED

• Confidentiality Impact
• LOW

• Availability Impact
• NONE

• Base Score
• 5.8

• Base Severity
• MEDIUM

• Exploitability Score
• 3.9

• Impact Score
• 1.4