CVE-2026-57079: Net::BitTorrent versions before 2.1.0 for Perl write files outside the download directory via path traversal in peer-supplied metadata

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-06-30 · updated 2026-10-25
Weakness: CWE-22

Description

Net::BitTorrent versions before 2.1.0 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.

Affected products

SANKO Net::BitTorrent: before 2.1.0 — fixed in 2.1.0

How to fix

Upgrade to a fixed version: SANKO Net::BitTorrent 2.1.0. Check the vendor advisory for mitigations.

References

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