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Net-BitTorrent-v2.1.0
⭐ Starred 13 / Net::BitTorrent::Protocol::BEP03
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::Protocol::BEP03 - Core BitTorrent Peer Wire Protocol

SYNOPSIS

use Net::BitTorrent::Protocol::BEP03;

my $proto = Net::BitTorrent::Protocol::BEP03->new(
    infohash => $ih,
    peer_id  => $id
);

# Generate initial handshake
my $out = $proto->write_buffer( );

# Process incoming bytes from the socket
$proto->receive_data( $raw_bytes );

# Send a custom message
$proto->send_message( 4, pack('N', $piece_index) ); # HAVE

DESCRIPTION

Net::BitTorrent::Protocol::BEP03 implements the foundational BitTorrent Peer Wire Protocol (BEP 03). It is a stateful, loop-agnostic parser and generator for the binary messages exchanged between peers over TCP (or uTP).

This module handles the initial handshake, reserved bit negotiation, and the framing of all standard messages (choke, unchoke, interested, have, bitfield, request, piece, etc.).

METHODS

new( %params )

Creates a new BEP03 protocol handler.

Expected parameters:

infohash

The 20 or 32-byte binary infohash.

peer_id

The local 20-byte binary peer ID.

reserved - optional

The 8-byte reserved bits string.

send_handshake( )

Sends the initial protocol handshake.

$proto->send_handshake();

receive_data( $data )

Feeds raw data into the protocol parser.

$proto->receive_data( $chunk );

Expected parameters:

$data

The binary data received from the transport.

write_buffer( )

Returns pending messages from the output buffer.

my $out = $proto->write_buffer();

send_message( $id, [$payload] )

Queues a protocol message.

$proto->send_message( 4, pack('N', 42) ); # HAVE piece 42

Expected parameters:

$id

The numeric message ID.

$payload - optional

The raw binary payload.

send_keepalive( )

Queues a keep-alive message.

$proto->send_keepalive();

send_choke( )

Sends a CHOKE message.

send_unchoke( )

Sends an UNCHOKE message.

send_interested( )

Sends an INTERESTED message.

send_not_interested( )

Sends a NOT_INTERESTED message.

send_have( $index )

Sends a HAVE message.

Expected parameters:

$index

The piece index.

send_bitfield( $data )

Sends a BITFIELD message.

Expected parameters:

$data

The binary bitfield data.

set_reserved_bit( $byte, $mask )

Sets a bit in the reserved bytes of the handshake.

$proto->set_reserved_bit( 5, 0x10 );

Expected parameters:

$byte

The byte index (0-7).

$mask

The bitmask to apply.

handshake event

Emitted when a handshake is successfully received.

$proto->on( handshake => sub ( $self, $ih, $id ) { ... } );

Expected parameters:

$ih

The 20 or 32-byte binary infohash.

$id

The 20-byte binary peer ID.

peer_id( )

Returns the local peer ID.

reserved( )

Returns or sets the reserved bytes string.

Expected parameters:

$val - optional

The new 8-byte reserved string.

state( )

Returns the current protocol state ('HANDSHAKE', 'OPEN', or 'CLOSED').

detected_ih( )

Returns the infohash detected during the handshake (useful for trackers/servers).

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.