id: CVE-2023-48795

info:
  name: OpenSSH Terrapin Attack - Detection
  author: pussycat0x
  severity: medium
  description: |
    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.
  remediation: |
    One can address this vulnerability by temporarily disabling the affected chacha20-poly1305@openssh.com encryption and -etm@openssh.com MAC algorithms in the configuration of the SSH server (or client), and instead utilize unaffected algorithms like AES-GCM.
  reference:
    - https://github.com/RUB-NDS/Terrapin-Scanner
    - https://terrapin-attack.com/
    - http://packetstormsecurity.com/files/176280/Terrapin-SSH-Connection-Weakening.html
    - http://seclists.org/fulldisclosure/2024/Mar/21
    - http://www.openwall.com/lists/oss-security/2023/12/18/3
  classification:
    cvss-metrics: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
    cvss-score: 5.9
    cve-id: CVE-2023-48795
    cwe-id: CWE-354
    epss-score: 0.69474
    epss-percentile: 0.97955
    cpe: cpe:2.3:a:openbsd:openssh:*:*:*:*:*:*:*:*
  metadata:
    verified: true
    max-request: 1
    vendor: openbsd
    product: openssh
    shodan-query:
      - product:"OpenSSH"
      - product:"openssh"
      - cpe:"cpe:2.3:a:openbsd:openssh"
  tags: cve,cve2023,packetstorm,seclists,js,ssh,network,passive,openbsd

javascript:
  - pre-condition: |
      isPortOpen(Host,Port);
    code: |
      const m = require("nuclei/ssh");
      const c = m.SSHClient();
      const response = c.ConnectSSHInfoMode(Host, Port);

      function SupportsChaCha20()
      {
      const CiphersClientServer = response.ServerKex.CiphersClientServer;
      const csexists = CiphersClientServer.includes("chacha20-poly1305@openssh.com");
      csexists;
      const CiphersServerClient = response.ServerKex.CiphersServerClient;
      const scexist = CiphersServerClient.includes("chacha20-poly1305@openssh.com");
      scexist;
      return csexists || scexist;
      }

      function SupportsCbcEtm()
      {
      const EncryCCS = response.ServerKex.CiphersClientServer;
      const EncryCCSsuf = EncryCCS.some(value => value.endsWith("-cbc"));
      EncryCCSsuf;

      const Macacs = response.ServerKex.MACsClientServer;
      const MacacsSuf = Macacs.some(value => value.endsWith("-etm@openssh.com"));
      MacacsSuf;

      const EncrySC = response.ServerKex.CiphersServerClient;
      const EncrySCSuf = EncrySC.some(value => value.endsWith("-cbc"));
      EncrySCSuf;

      const Macasc = response.ServerKex.MACsServerClient;
      const MacascSuf = Macasc.some(value => value.endsWith("-etm@openssh.com"));
      MacascSuf;
      return EncryCCSsuf && MacacsSuf || EncrySCSuf && MacascSuf;

      }

      function SupportsStrictKex()
      {
      const SuStrictKex = response.ServerKex.KexAlgos;
      const hasSuffix = SuStrictKex.some(value => value.endsWith("kex-strict-s-v00@openssh.com"));
      return hasSuffix;

      }

      function  IsVulnerable()
      {
      const vuln = ((SupportsChaCha20() || SupportsCbcEtm()) && ! SupportsStrictKex())
        if (vuln === true) {
        return ("Vulnerable to Terrapin");
        }
        }
      Export(IsVulnerable())

    args:
      Host: "{{Host}}"
      Port: 22

    extractors:
      - type: dsl
        dsl:
          - response
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