AIKIDO-2026-139198

TL;DR

The attachment-writing helpers in the mail-parser library build output paths by joining a caller-supplied directory with the raw attachment filename taken from email metadata. Because the email sender fully controls that filename, values containing ../ sequences, absolute paths, or names that resolve through a symlink cause attachments to be written outside the intended output directory. This lets a crafted email create or overwrite arbitrary files on the host that runs the parser. The fix strips directory components from filenames, verifies the resolved path stays inside the output directory, rejects symlink destinations, and deduplicates names within an attachment batch.