CVE-2026-46671 msiemens CVE debrief

Who should care

Users of Rust OneNote File Parser who parse `.onetoc2` files received from untrusted sources are affected by this vulnerability. This includes developers and users who handle OneNote files from external sources. Users who only ever parse their own notebooks are not at meaningful risk. The vulnerability allows for arbitrary file opening on the host filesystem, which can lead to potential data breaches or system compromise.

Technical summary

Prior to version 1.1.1, a maliciously crafted `.onetoc2` table-of-contents file can cause `Parser::parse_notebook` 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 issue is fixed in onenote_parser 1.1.1. The fix involves rejecting absolute paths, parent-directory components, and other invalid path characters in entry names, and additionally canonicalising the resolved path to confirm it stays inside the notebook's base directory. Users who cannot upgrade to 1.1.1 should only call `Parser::parse_notebook` on `.onetoc2` files from trusted sources or use `Parser::parse_section` / `Parser::parse_section_buffer` on individual .one files.

Defensive priority

Medium-High

Recommended defensive actions

• Upgrade to onenote_parser 1.1.1 or later
• Only call `Parser::parse_notebook` on `.onetoc2` files from trusted sources
• Use `Parser::parse_section` / `Parser::parse_section_buffer` on individual .one files
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The issue is fixed in onenote_parser 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. Users who cannot upgrade to 1.1.1 should only call `Parser::parse_notebook` on `.onetoc2` files from trusted sources or use `Parser::parse_section` / `Parser::parse_section_buffer` on individual .one files. This ensures that the directory walk is properly confined and reduces the risk of arbitrary file opening.

Official resources