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Net-BitTorrent-v2.0.1
⭐ Starred 13 / Net::BitTorrent::Tracker
Security Advisories (4)
CVE-2026-57079 (2026-06-30)

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.

CVE-2026-57080 (2026-06-30)

Net::BitTorrent versions through 2.0.1 for Perl allow remote memory exhaustion via an uncapped peer-wire message-length prefix. The peer-wire framing in _process_messages trusts the 4-byte length prefix sent by a connected peer with no upper bound, while receive_data appends every inbound byte to the input buffer. A peer announces a length prefix of up to about 4 GiB and then streams bytes; the decoder waits until the buffer holds the full message before processing it, so the buffer grows without limit. Peer connections are unauthenticated, so any peer in the swarm exhausts the downloading process's memory. The largest legitimate message is a 16 KiB piece block, so any announced length far above that is anomalous.

CVE-2026-57082 (2026-06-30)

Net::BitTorrent versions through 2.0.1 for Perl generate the MSE Diffie-Hellman private key with a non-cryptographic PRNG. The MSE (Message Stream Encryption) handshake derives its 160-bit Diffie-Hellman private key from Perl's rand(), a non-cryptographic drand48-class generator seeded once per process, in KeyExchange.pm. The shared secret and the RC4 keys derived from it (the SHA-1 of "keyA" or "keyB", the shared secret, and the infohash) therefore depend entirely on a predictable PRNG. The same handshake sends, in cleartext, random padding drawn from the same rand() sequence in _random_pad, immediately after the public key and the private-key draw. A passive observer of the handshake recovers the PRNG state from the cleartext padding, reconstructs the private key, computes the shared secret from the peer's public key on the wire, derives the RC4 keys, and decrypts the connection, defeating the passive-observation obfuscation MSE provides.

CVE-2026-57081 (2026-06-30)

Net::BitTorrent versions through 2.0.1 for Perl allow remote memory exhaustion via deeply nested bencoded input. bdecode recurses once per nested list or dictionary level with no depth cap, and each recursive call receives the remaining buffer by value while the list and dictionary branches capture the whole remainder, so every live recursion frame keeps its own copy of the shrinking buffer (O(N^2) bytes for an N-deep input). The decoder runs on every untrusted bencode source: .torrent files, BEP09 metadata fetched from peers, DHT messages, and tracker responses. A bencoded input of roughly 150,000 nested lists (about 150 KB on the wire) drives multi-gigabyte peak memory, so one short message from any peer, or one crafted .torrent file or magnet link, terminates the client.

NAME

Net::BitTorrent::Tracker - Multi-tier Tracker Manager

SYNOPSIS

use Net::BitTorrent::Tracker;

my $manager = Net::BitTorrent::Tracker->new(
    tiers_raw => [
        ['udp://tracker.openbittorrent.com:80/announce'],
        ['http://tracker.example.com/announce', 'https://another.net/announce']
    ]
);

# Announce presence and get peers
$manager->announce_all({
    infohash   => $bin_ih,
    peer_id    => $my_id,
    port       => 6881,
    downloaded => 0,
    uploaded   => 0,
    left       => 1024,
    event      => 'started'
}, sub ($peers) {
    say "Found " . scalar(@$peers) . " peers!";
});

DESCRIPTION

Net::BitTorrent::Tracker manages communication with external trackers. It implements the Multi-tracker Metadata (BEP 12) specification, handling tiers, retries, and backoff logic.

Protocol Support

The manager automatically detects and handles multiple tracker protocols:

  • UDP (BEP 15): Lightweight, preferred transport.

  • HTTP/HTTPS: Standard bencoded announce protocol.

METHODS

new( %params )

Creates a new Tracker manager.

my $manager = Net::BitTorrent::Tracker->new(
    tiers_raw => [ ['http://tracker.example.com/announce'] ]
);

This method initializes the tracker manager with a list of tracker tiers.

Expected parameters:

tiers_raw

An array reference of array references, where each inner array contains tracker URLs for a single tier.

debug - optional

Whether to enable debug logging.

announce_all( \%params, [$callback] )

Announces to all tracker tiers.

$manager->announce_all({
    infohash => $ih,
    peer_id  => $id,
    port     => 6881,
    left     => 1000
}, sub ($peers) { ... });

This method iterates through tracker tiers (BEP 12), announcing presence and gathering peers. It returns an array reference of unique peer structures discovered.

Expected parameters:

\%params

Standard announce parameters (infohash, peer_id, port, uploaded, downloaded, left, event).

$callback - optional

A code reference called with an arrayref of peer structures ({ip, port}) when peers are received.

scrape_all( \@infohashes, [$callback] )

Scrapes all trackers for swarm stats.

$manager->scrape_all([$ih1, $ih2], sub ($stats) { ... });

This method queries all trackers for seeder/leecher counts (BEP 48). It returns a hash reference of statistics.

Expected parameters:

\@infohashes

An array reference of binary infohashes to scrape.

$callback - optional

A code reference called with a hash reference of statistics per infohash.

trackers( )

Returns a list of all tracker URLs.

my $list = $manager->trackers();

This method returns a flattened array reference of all managed tracker URLs.

tick( $delta )

Performs periodic maintenance for all trackers.

$manager->tick( 0.1 );

This method allows individual tracker objects to process timeouts and retransmissions.

Expected parameters:

$delta

The time elapsed since the last tick in seconds.

add_tracker( $url )

Adds a new tracker to the manager.

$manager->add_tracker( 'udp://new.tracker.com:6969/announce' );

This method adds a new tracker URL as a new tier if it is not already present.

Expected parameters:

$url

The URL of the tracker to add.

SEE ALSO

Net::BitTorrent::Tracker::HTTP, Net::BitTorrent::Tracker::UDP

AUTHOR

Sanko Robinson <sanko@cpan.org>

COPYRIGHT

Copyright (C) 2008-2026 by Sanko Robinson.

This library is free software; you can redistribute it and/or modify it under the terms of the Artistic License 2.0.