HedgeDoc is software for creating real-time collaborative markdown notes. Prior to version 1.9.9, the API of HedgeDoc 1 can be used to create notes with an alias matching the ID of existing notes. The affected existing note can then not be accessed anymore and is effectively hidden by the new one.
When the freeURL feature is enabled (by setting the `allowFreeURL` config option or the `CMD_ALLOW_FREEURL` environment variable to `true`), any user with the appropriate permissions can create a note by making a POST request to the `/new/<ALIAS>` API endpoint. The `<ALIAS>` parameter can be set to the ID of an existing note. HedgeDoc did not verify whether the provided `<ALIAS>` value corresponds to a valid ID of an existing note and always allowed creation of the new note. When a visitor tried to access the existing note, HedgeDoc will first search for a note with a matching alias before it searches using the ID, therefore only the new note can be accessed.
Depending on the permission settings of the HedgeDoc instance, the issue can be exploited only by logged-in users or by all (including non-logged-in) users. The exploit requires knowledge of the ID of the target note. Attackers could use this issue to present a manipulated copy of the original note to the user, e.g. by replacing the links with malicious ones. Attackers can also use this issue to prevent access to the original note, causing a denial of service. No data is lost, as the original content of the affected notes is still present in the database.
This issue was fixed in version 1.9.9. As a workaround, disabling freeURL mode prevents the exploitation of this issue. The impact can be limited by restricting freeURL note creation to trusted, logged-in users by enabling `requireFreeURLAuthentication`/`CMD_REQUIRE_FREEURL_AUTHENTICATION`.
HedgeDoc is software for creating real-time collaborative markdown notes. Prior to version 1.9.9, the API of HedgeDoc 1 can be used to create notes with an alias matching the ID of existing notes. The affected existing note can then not be accessed anymore and is effectively hidden by the new one.
When the freeURL feature is enabled (by setting the `allowFreeURL` config option or the `CMD_ALLOW_FREEURL` environment variable to `true`), any user with the appropriate permissions can create a note by making a POST request to the `/new/[ALIAS]` API endpoint. The `[ALIAS]` parameter can be set to the ID of an existing note. HedgeDoc did not verify whether the provided `[ALIAS]` value corresponds to a valid ID of an existing note and always allowed creation of the new note. When a visitor tried to access the existing note, HedgeDoc will first search for a note with a matching alias before it searches using the ID, therefore only the new note can be accessed.
Dependiendo de la configuración de permisos de la instancia de HedgeDoc, el problema puede ser explotado sólo por usuarios que hayan iniciado sesión o por todos los usuarios (incluidos los que no hayan iniciado sesión). El exploit requiere conocer el ID de la nota objetivo. Los atacantes podrían utilizar este problema para presentar al usuario una copia manipulada de la nota original, por ejemplo, sustituyendo los enlaces por otros maliciosos. Los atacantes también pueden utilizar este problema para impedir el acceso a la nota original, provocando una denegación de servicio. No se pierde ningún dato, ya que el contenido original de las notas afectadas sigue presente en la base de datos.
Este problema se solucionó en la versión 1.9.9. Como solución provisional, desactivar el modo freeURL impide la explotación de este problema. El impacto puede limitarse restringiendo la creación de notas freeURL a usuarios de confianza que hayan iniciado sesión, habilitando `requireFreeURLAuthentication`/`CMD_REQUIRE_FREEURL_AUTHENTICATION`.
