CVE-2026-46671 is a CWE-22 path traversal vulnerability in the Rust OneNote File Parser (onenote.rs) affecting versions prior to 1.1.1. The parse_notebook method processes .onetoc2 table-of-contents files by joining entry names to the notebook base directory without validating that these paths remain within the directory. This allows an attacker to craft a .onetoc2 file that causes the parser to open arbitrary files on the host filesystem outside the notebook directory. Although direct content exfiltration via the parser's output is not practical, the vulnerability enables file existence probing and denial-of-service attacks via large or special files. The vulnerability is fixed in version 1.1.1 by rejecting absolute paths, parent-directory components, and invalid characters, and by canonicalizing paths to confirm confinement within the notebook directory. Users unable to upgrade should only parse .onetoc2 files from trusted sources or use alternative parsing methods that do not perform directory walks.

An attacker who can supply a malicious .onetoc2 file to the parser can cause it to open arbitrary files outside the intended notebook directory. This can lead to file existence probing and denial-of-service conditions due to processing large or special files. However, the parser will abort if the file does not parse as a OneNote section, limiting direct content exfiltration through the parser's return value. The vulnerability requires local access to supply crafted files and user interaction to trigger parsing. The CVSS score is 4.4 (medium severity) reflecting limited confidentiality impact and local attack vector.

A fix is available in onenote_parser version 1.1.1, which validates and canonicalizes paths to prevent traversal outside the notebook directory. Users should upgrade to version 1.1.1 or later. For those unable to upgrade, only parse .onetoc2 files from trusted sources. Alternatively, use Parser::parse_section or Parser::parse_section_buffer on individual .one files, which do not perform directory traversal. There is no vendor advisory explicitly stating no action required; therefore, these mitigations are recommended.