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Net-BitTorrent-v2.0.1
⭐ Starred 13 / Net::BitTorrent::Protocol::BEP52
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::Protocol::BEP52 - BitTorrent v2 Protocol Extensions

SYNOPSIS

# Inherits from Net::BitTorrent::Protocol::BEP03
use Net::BitTorrent::Protocol::BEP52;

my $p = Net::BitTorrent::Protocol::BEP52->new( ... );

# Request hashes for a Merkle tree
$p->send_hash_request( $pieces_root, $proof_layer, $base_layer, $index, $count );

DESCRIPTION

Net::BitTorrent::Protocol::BEP52 extends the standard peer wire protocol with support for BitTorrent v2 (BEP 52). It specifically handles the synchronization of Merkle tree hashes between peers, which is required for block-level data verification.

Unlike v1, where piece hashes are contained in the .torrent file, v2 uses a dynamic hash fetching mechanism. When a peer receives a block, it may need to request the corresponding Merkle proof nodes from the swarm to verify the block data. This module provides the wire-format messages to perform these requests.

It is typically used via Net::BitTorrent::Protocol::PeerHandler.

METHODS

send_hash_request( $pieces_root, $proof_layer, $base_layer, $index, $length )

Sends a request for a range of hashes.

$p->send_hash_request( $root, 0, 0, 0, 10 );

This method sends a HASH_REQUEST (ID 21) message to retrieve hashes required for v2 piece verification.

Expected parameters:

$pieces_root

The 32-byte binary SHA-256 Merkle root of the file.

$proof_layer

The layer index for proof nodes.

$base_layer

The layer index for the requested hashes.

$index

The starting node index in the base layer.

$length

The number of hashes requested.

send_hashes( $pieces_root, $proof_layer, $base_layer, $index, $length, $hashes )

Sends a response with hashes.

$p->send_hashes( $root, 0, 0, 0, 1, $hash_data );

This method sends a HASHES (ID 22) message containing the requested binary hashes.

Expected parameters:

$pieces_root

The 32-byte Merkle root.

$proof_layer

The proof layer index.

$base_layer

The base layer index.

$index

The starting index.

$length

The number of hashes included.

$hashes

The concatenated binary hashes.

send_hash_reject( $pieces_root, $proof_layer, $base_layer, $index, $length )

Rejects a hash request.

$p->send_hash_reject( $root, 0, 0, 0, 10 );

This method sends a HASH_REJECT (ID 23) message.

Expected parameters:

$pieces_root

The 32-byte Merkle root.

$proof_layer

The proof layer index.

$base_layer

The base layer index.

$index

The starting index.

$length

The number of hashes rejected.

hash_request event

Emitted when a hash request is received.

$p->on( hash_request => sub ( $self, $root, $proof, $base, $idx, $len ) { ... } );

Expected parameters:

$root

The 32-byte Merkle root.

$proof

The proof layer.

$base

The base layer.

$idx

The starting index.

$len

The length requested.

hashes event

Emitted when hashes are received.

$p->on( hashes => sub ( $self, $root, $proof, $base, $idx, $len, $hashes ) { ... } );

Expected parameters:

$root

The 32-byte Merkle root.

$proof

The proof layer.

$base

The base layer.

$idx

The starting index.

$len

The number of hashes.

$hashes

The binary hash data.

hash_reject event

Emitted when a hash request is rejected.

$p->on( hash_reject => sub ( $self, $root, $proof, $base, $idx, $len ) { ... } );

Expected parameters:

$root

The 32-byte Merkle root.

$proof

The proof layer.

$base

The base layer.

$idx

The starting index.

$len

The rejected length.

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.