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Fencer Vulns
medium 5.9

CVE-2026-57082 json

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

published 2026-06-30 4 mo ago modified 2026-10-25 14 d ago also EUVD-2026-40291

cvss
5.9
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 14%
public exploits
0
none known

Summary

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.

Patch / fix

  • SANKO Net::BitTorrent 2.1.0

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
4 mo ago

Exploit prediction

0.23% chance of exploitation in the next 30 days, higher than 14% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CISA ADP 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
CNA 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Affected products

  • SANKO Net::BitTorrent

Classification

Weakness
  • CWE-338 Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)
  • CWE-330 Use of Insufficiently Random Values

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.