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authorSheogorath2021-03-23 00:02:30 +0100
committerSheogorath2021-04-25 20:40:17 +0200
commit44b7f607a542abc2f47ac141f2fd6cd1d34ed1c5 (patch)
tree30013f2d8085ce04c004c6389725c4beb9c2cb36 /docs/content
parent2ea40bb98d80ca765f60f9b69d26d5be12188231 (diff)
Fix Relative Path Traversal Attack on note creation
Impact --- An attacker can read arbitrary `.md` files from the server's filesystem due to an [improper input validation](https://cwe.mitre.org/data/definitions/20.html), which results in the ability to perform a [relative path traversal](https://cwe.mitre.org/data/definitions/23.html). CVSSv3 string: AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N PoC / Quicktest --- 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. Analysis --- The attack works due the fact that [the internal router, passes the url-encoded alias](https://github.com/hedgedoc/hedgedoc/blob/master/lib/web/note/router.js#L26) to the `noteController.showNote`-function. This function passes the input directly to [`findNote()`](https://github.com/hedgedoc/hedgedoc/blob/78a732abe691b496fa3692aa2add37f7344db1fa/lib/web/note/util.js#L10) utility function, that will pass it on the the [`parseNoteId()`](https://github.com/hedgedoc/hedgedoc/blob/78a732abe691b496fa3692aa2add37f7344db1fa/lib/models/note.js#L188-L258)-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](https://github.com/hedgedoc/hedgedoc/blob/78a732abe691b496fa3692aa2add37f7344db1fa/lib/models/note.js#L240-L245), which pass this unvalidated alias, with a `.md` appended, into a [`path.join()`-function](https://github.com/hedgedoc/hedgedoc/blob/78a732abe691b496fa3692aa2add37f7344db1fa/lib/models/note.js#L99) 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. Workarounds --- 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. For more information --- If you have any questions or comments about this advisory: * Open an topic on [our community forum](https://community.hedgedoc.org) * Join our [matrix room](https://chat.hedgedoc.org) Advisory link --- https://github.com/hedgedoc/hedgedoc/security/advisories/GHSA-p528-555r-pf87 Signed-off-by: Christoph (Sheogorath) Kern <sheogorath@shivering-isles.com>
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