CVE-2023-48795 (JavaScript, published 2023-12-18T16:15Z)
Description: value: The SSH transport protocol with certain OpenSSH extensions, found in OpenSSH before 9.6 and other products, allows remote attackers to bypass integrity checks such that some packets are omitted (from the extension negotiation message), and a client and server may consequently end up with a connection for which some security features have been downgraded or disabled, aka a Terrapin attack. This occurs because the SSH Binary Packet Protocol (BPP), implemented by these extensions, mishandles the handshake phase and mishandles use of sequence numbers. For example, there is an effective attack against SSH's use of ChaCha20-Poly1305 (and CBC with Encrypt-then-MAC). The bypass occurs in chacha20-poly1305@openssh.com and (if CBC is used) the -etm@openssh.com MAC algorithms. This also affects Maverick Synergy Java SSH API before 3.1.0-SNAPSHOT, Dropbear through 2022.83, Ssh before 5.1.1 in Erlang/OTP, PuTTY before 0.80, AsyncSSH before 2.14.2, golang.org/x/crypto before 0.17.0, libssh before 0.10.6, libssh2 through 1.11.0, Thorn Tech SFTP Gateway before 3.4.6, Tera Term before 5.1, Paramiko before 3.4.0, jsch before 0.2.15, SFTPGo before 2.5.6, Netgate pfSense Plus through 23.09.1, Netgate pfSense CE through 2.7.2, HPN-SSH through 18.2.0, ProFTPD before 1.3.8b (and before 1.3.9rc2), ORYX CycloneSSH before 2.3.4, NetSarang XShell 7 before Build 0144, CrushFTP before 10.6.0, ConnectBot SSH library before 2.2.22, Apache MINA sshd through 2.11.0, sshj through 0.37.0, TinySSH through 20230101, trilead-ssh2 6401, LANCOM LCOS and LANconfig, FileZilla before 3.66.4, Nova before 11.8, PKIX-SSH before 14.4, SecureCRT before 9.4.3, Transmit5 before 5.10.4, Win32-OpenSSH before 9.5.0.0p1-Beta, WinSCP before 6.2.2, Bitvise SSH Server before 9.32, Bitvise SSH Client before 9.33, KiTTY through 0.76.1.13, the net-ssh gem 7.2.0 for Ruby, the mscdex ssh2 module before 1.15.0 for Node.js, the thrussh library before 0.35.1 for Rust, and the Russh crate before 0.40.2 for Rust.
Severity: nan (CVSS v3 base score: 5.9)
Weakness: CWE-354 \u2014 Improper Validation of Integrity Check Value
The product does not validate or incorrectly validates the integrity check values or "checksums" of a message. This may prevent it from detecting if the data has been modified or corrupted in transmission.
Repository: https://github.com/mscdex/ssh2
Files changed:
lib/protocol/Protocol.js
lib/protocol/kex.js
lib/server.js
Commit message: lib: add strict key exchange mode support


Vulnerable code:
      if (!this._server)
        offer.kex = offer.kex.concat(['ext-info-c']);
    debug && debug('Handshake: No matching key exchange algorithm');
    case MESSAGE.IGNORE:
    case MESSAGE.UNIMPLEMENTED:
    case MESSAGE.DEBUG:
    kex: DEFAULT_KEX.concat(['ext-info-c']),
    kex: DEFAULT_KEX,
      kex: generateAlgorithmList(cfgAlgos.kex, DEFAULT_KEX, SUPPORTED_KEX),

Fixed code:
      if (this._server) {
        offer.kex = offer.kex.concat(['kex-strict-s-v00@openssh.com']);
      } else {
        offer.kex = offer.kex.concat([
          'ext-info-c',
          'kex-strict-c-v00@openssh.com',
        ]);
      }
    this._strictMode = undefined;
  if (self._strictMode === undefined) {
    if (self._server) {
      self._strictMode =
        (clientList.indexOf('kex-strict-c-v00@openssh.com') !== -1);
    } else {
      self._strictMode =
        (serverList.indexOf('kex-strict-s-v00@openssh.com') !== -1);
    }
    // Note: We check for seqno of 1 instead of 0 since we increment before
    //       calling the packet handler
    if (self._strictMode) {
      debug && debug('Handshake: strict KEX mode enabled');
      if (self._decipher.inSeqno !== 1) {
        if (debug)
          debug('Handshake: KEXINIT not first packet in strict KEX mode');
        return doFatalError(
          self,
          'Handshake failed: KEXINIT not first packet in strict KEX mode',
          'handshake',
          DISCONNECT_REASON.KEY_EXCHANGE_FAILED
        );
      }
    }
  }
    debug && debug('Handshake: no matching key exchange algorithm');
          if (this._protocol._strictMode)
            this._protocol._decipher.inSeqno = 0;

  if (!this._strictMode) {
    switch (type) {
      case MESSAGE.IGNORE:
      case MESSAGE.UNIMPLEMENTED:
      case MESSAGE.DEBUG:
        if (!MESSAGE_HANDLERS)
          MESSAGE_HANDLERS = require('./handlers.js');
        return MESSAGE_HANDLERS[type](this, payload);
    }
  }

      // Ensure packet is either an algorithm negotiation or KEX
      // algorithm-specific packet
    if (kex._protocol._strictMode)
      kex._protocol._cipher.outSeqno = 0;
    kex: DEFAULT_KEX.concat(['ext-info-c', 'kex-strict-c-v00@openssh.com']),
    kex: DEFAULT_KEX.concat(['kex-strict-s-v00@openssh.com']),
      kex: generateAlgorithmList(
        cfgAlgos.kex,
        DEFAULT_KEX,
        SUPPORTED_KEX
      ).concat(['kex-strict-s-v00@openssh.com']),