Summary A path traversal vulnerability in the OneNote importer allows overwriting arbitrary files on disk.

Details The OneNote converter does not sanitize the names of embedded files before writing them to disk. As a result, it's possible for an attacker to create a malicious .one file that includes file names containing ../../, that are then interpreted as part of the target path when extracting attachments from the .one file.

One affected location is embeddedfile.rs, which generates a file name from a string previously parsed from the .one file, https://github.com/laurent22/joplin/blob/af5108d70233b1db9410346958c1587cf7c1b16d/packages/onenote-converter/renderer/src/page/embeddedfile.rs#L13-L16

Above, determinefilename passes through the provided file name.

Similar logic has been present since 4d7fa5972fe2986eae14cbf3a2801835cbe1384e (Joplin 3.2.2), when the OneNote importer was first introduced.

PoC

Screencast from 2025-11-20 13-50-21.webm

1. Import pocv2.zip. 2. Open the application's profile directory, then open log.txt. 3. Observe that log.txt has been overwritten non-log-file content (a WAV file).

Tested on Fedora Linux 43 with Joplin 3.4.12 (prod, linux) and Joplin 3.5.6 (dev, linux).

Note: The PoC ZIP file overwrites Joplin's log.txt. It is also possible to craft a file that overwrites more sensitive system files (e.g. .bashrc on Linux).

Impact This is a path traversal vulnerability that impacts all versions of Joplin (<= v3.5.6) that include a OneNote importer. Importing a crafted OneNote export file allows an attacker to overwrite arbitrary files, potentially leading to remote code execution.

Patched in

- Joplin: https://github.com/laurent22/joplin/commit/791668455e1aae50501ff57ea4783b3fba9d377c - one2html: https://github.com/msiemens/one2html/commit/948d65cdca5bb35d776b8b235ec05ff15249fd41

Impact A maliciously crafted .onetoc2 table-of-contents file can cause Parser::parsenotebook to open arbitrary files on the host filesystem outside the notebook's directory. The parser reads entry names listed inside the .onetoc2 and joins them against the notebook's base directory without validating that they are relative paths confined to that directory.

The parser will bail out when the target file fails to parse as a OneNote section, so direct content exfiltration through the parser's return value is not practical, though file-existence probing and denial-of-service via large or special files remain possible.

Anyone using onenoteparser to parse .onetoc2 files received from untrusted sources is affected. Users who only ever parse their own notebooks are not at meaningful risk.

Patches Fixed in onenoteparser 1.1.1. The fix rejects absolute paths, parent-directory components, and other invalid path characters in entry names, and additionally canonicalises the resolved path to confirm it stays inside the notebook's base directory.

Workarounds For users who cannot upgrade to 1.1.1:

- Only call Parser::parsenotebook on .onetoc2 files from trusted sources. - Alternatively, use Parser::parsesection / Parser::parsesectionbuffer on individual .one files, which do not perform the directory walk.