{"id":"CVE-2021-29474","details":"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.","modified":"2026-04-12T02:45:40.496554Z","published":"2021-04-26T22:15:08.900Z","related":["GHSA-p528-555r-pf87"],"references":[{"type":"FIX","url":"https://github.com/hedgedoc/hedgedoc/security/advisories/GHSA-p528-555r-pf87"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/hedgedoc/hedgedoc","events":[{"introduced":"0"},{"fixed":"f48e36d2052bcae56081bee3c281bfc69fe7f70d"}],"database_specific":{"cpe":"cpe:2.3:a:hedgedoc:hedgedoc:*:*:*:*:*:*:*:*","extracted_events":[{"introduced":"0"},{"fixed":"1.8.0"}],"source":"CPE_FIELD"}}],"versions":["0.4.0","0.4.1","0.4.2","0.4.3","0.4.4","0.4.5","0.4.6","0.5.0","1.0.0-ce","1.0.1-ce","1.1.0-ce","1.1.1-ce","1.2.0","1.2.1","1.3.0","1.3.1","1.3.2","1.4.0","1.5.0","1.6.0","1.7.0","1.7.0-rc1","1.7.0-rc2","1.7.1","1.7.2","1.8.0-rc1","v0.3.3","v0.3.4"],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2021-29474.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:N/A:N"}]}