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Net-BitTorrent-v2.1.0
⭐ Starred 13 / Net::BitTorrent::Tracker::WebSeed
Security Advisories (2)
CVE-2026-57080 (2026-06-30)

Net::BitTorrent versions through 2.1.0 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-2026-57081 (2026-06-30)

Net::BitTorrent versions through 2.1.0 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::WebSeed - HTTP WebSeed Client (BEP 19 / BEP 17)

SYNOPSIS

use Net::BitTorrent::Tracker::WebSeed;

my $ws = Net::BitTorrent::Tracker::WebSeed->new(
    url => "https://archive.org/download/my_torrent/"
);

# Fetch a piece using segments mapped by the storage layer
my $data = $ws->fetch_piece([
    { rel_path => "file1.bin", offset => 0, length => 16384 }
]);

say "Successfully fetched piece" if $data;

DESCRIPTION

Net::BitTorrent::Tracker::WebSeed implements BEP 19 (WebSeeding). It allows a client to download pieces of a torrent from a standard HTTP or FTP server. This is highly effective for ensuring swarm availability when no regular BitTorrent seeders are online.

METHODS

new( %params )

Creates a new WebSeed object.

my $ws = Net::BitTorrent::Tracker::WebSeed->new(
    url => $base_url
);

Expected parameters:

url

The base URL of the web seed.

fetch_piece( $segments )

Attempts to fetch a piece from the web seed.

my $data = $ws->fetch_piece( $segments );

Expected parameters:

$segments

An array reference of segments, each containing file, offset, and length.

Uses HTTP Range requests to fetch only the specific bytes required for the piece. Automatically follows up to 5 redirects. Handles 410 Gone status codes by permanently disabling the web seed instance.

fetch_piece_legacy( $index, $piece_length, $total_size )

Legacy method for fetching a single piece from a single-file torrent.

my $data = $ws->fetch_piece_legacy( 0, 262144, 1048576 );

Expected parameters:

$index

The piece index.

$piece_length

The piece length in bytes.

$total_size

The total size of the file.

url( )

Returns the base URL of the web seed.

disabled( )

Returns true if the web seed has been disabled (e.g., due to 410 Gone).

Architecture

For multi-file torrents, if the URL ends in a slash (/), the module automatically appends the relative path of each file within the swarm to build the target URL.

This module is designed to be called by Net::BitTorrent::Torrent when a piece cannot be found in the P2P swarm.

Specifications

  • BEP 19: WebSeed - HTTP/FTP Seeding (GetRight style)

  • BEP 17: HTTP Seeding (Hoffman-style)

AUTHOR

Sanko Robinson - https://github.com/sanko

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.