CVE-2026-57079
MediumCVSS 5.3Summary
A vulnerability in the Net::BitTorrent library for Perl (up to version 2.0.1) allows writing files outside the download directory via path traversal in peer-supplied metadata. An attacker can exploit the ut_metadata extension (BEP09) to supply file names containing ".." sequences that are not properly validated.
Risk Assessment
The organization is at risk of remote arbitrary file overwrite on the downloading host with attacker-controlled content. This could lead to system compromise, code injection, or data integrity violation.
Recommendation
Immediately update Net::BitTorrent to version 2.0.2 or later, which includes a fix for this vulnerability. If an update is not possible, temporarily disable the ut_metadata extension (magnet links) in applications using this library.
Original NVD description (English source)
Net::BitTorrent versions through 2.0.1 for Perl write files outside the download directory via path traversal in peer-supplied metadata. Net::BitTorrent validates file path components only on the .torrent-file ingest path. The peer and magnet metadata path (_on_metadata_received, reached from the BEP09 ut_metadata extension) passes attacker-supplied file names straight to Storage::add_file and Storage::_parse_file_tree, where Path::Tiny's child() does not collapse "..". A v2 file tree key, a v1 files[].path element, or a single-file name containing ".." segments therefore resolves outside the download directory. Because the peer also controls the piece hashes and the served bytes, content verification passes, so a malicious magnet or peer writes attacker-chosen content to an attacker-chosen path on the downloading host.