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Net-BitTorrent-v2.1.0
⭐ Starred 13 / Net::BitTorrent::Protocol::BEP10
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::BEP10 - Extension Protocol Implementation

SYNOPSIS

# Inherits from Net::BitTorrent::Protocol::BEP52 (BitTorrent v2)
use Net::BitTorrent::Protocol::BEP10;

my $proto = Net::BitTorrent::Protocol::BEP10->new(
    local_extensions => { ut_metadata => 1, ut_pex => 2 }
);

# Once core handshake is done, send extension handshake
$proto->send_ext_handshake();

# Send an extension message by name
$proto->send_ext_message( 'ut_pex', $bencoded_pex_data );

DESCRIPTION

Net::BitTorrent::Protocol::BEP10 implements the Extension Protocol (BEP 10). This is the standard mechanism modern BitTorrent clients use to negotiate support for additional features (like PEX, Magnet links, and DHT security) without needing to allocate new reserved bits in the foundational BitTorrent handshake.

METHODS

new( %params )

Creates a new BEP10 protocol handler.

Expected parameters:

local_extensions - optional

A hash reference mapping extension names to local IDs.

metadata_size - optional

The total size of the torrent metadata in bytes.

send_ext_handshake( )

Sends the extension protocol handshake.

$proto->send_ext_handshake();

This method sends the EXTENDED (ID 20) message with sub-ID 0, containing the local extension dictionary.

send_ext_message( $name, $payload )

Sends an extended message.

$proto->send_ext_message( 'ut_metadata', $data );

This method sends a message for a specific extension by its name.

Expected parameters:

$name

The string name of the extension (e.g., 'ut_metadata', 'ut_pex').

$payload

The raw message payload.

ext_handshake event

Emitted when an extended handshake is received.

$proto->on( ext_handshake => sub ( $self, $data ) { ... } );

Expected parameters:

$data

The decoded handshake dictionary (hash reference).

extended_message event

Emitted when an extended message is received.

$proto->on( extended_message => sub ( $self, $name, $payload ) { ... } );

Expected parameters:

$name

The name of the extension.

$payload

The raw message payload.

local_extensions( )

Returns the local extensions map.

my $exts = $proto->local_extensions();

remote_extensions( )

Returns the remote extensions map.

my $exts = $proto->remote_extensions();

remote_version( )

Returns the remote client's version string.

say "Remote version: " . $proto->remote_version();

remote_ip( )

Returns our external IP as seen by the remote peer.

say "Remote says our IP is: " . $proto->remote_ip();

metadata_size( )

Returns the total size of the metadata as reported by the peer.

my $size = $proto->metadata_size();

remote_extensions_received( )

Returns true if the remote extended handshake has been received.

if ($proto->remote_extensions_received) { ... }

SPECIFICATIONS

  • BEP 10: Extension Protocol

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.