CVE-2026-57082

Net::BitTorrent versions before 2.1.0 for Perl generate the MSE Diffie-Hellman private key with a non-cryptographic PRNG

Published Jun 30, 2026 CVSS 3.1 · 5.9 Medium EPSS < 1% KEV · Not listed
Description
Net::BitTorrent versions before 2.1.0 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.

Remediation

Vendor Solution

Upgrade to version 2.1.0 or later.

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
Description 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. Net::BitTorrent versions before 2.1.0 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.
Title Net::BitTorrent versions through 2.0.1 for Perl generate the MSE Diffie-Hellman private key with a non-cryptographic PRNG Net::BitTorrent versions before 2.1.0 for Perl generate the MSE Diffie-Hellman private key with a non-cryptographic PRNG
References
Type Values Removed Values Added
First Time appeared Sanko
Sanko net::bittorrent
Vendors & Products Sanko
Sanko net::bittorrent
Type Values Removed Values Added
Metrics cvssV3_1

{'score': 5.9, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N'}

ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
Description 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.
Title Net::BitTorrent versions through 2.0.1 for Perl generate the MSE Diffie-Hellman private key with a non-cryptographic PRNG
Weaknesses CWE-330
CWE-338
References
Weaknesses

Sources

Status
PUBLISHED
Assigner
CPANSec
Published
Updated
Jul 20, 2026, 6:43 AM
Reserved
Jun 23, 2026, 6:20 PM
Status
Deferred
Published
Jun 30, 2026, 12:16 PM
Modified
Oct 25, 2026, 9:10 PM