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.