SSL RC4 Cipher Suites Supported

Tenable plugin 65821 is not pointing to a single buggy product build; it is flagging any SSL/TLS service that will still negotiate an RC4 cipher suite, exposing it to the *Bar Mitzvah* class of attacks tracked as CVE-2015-2808. The affected population is therefore broad but narrow in practice: any server, appliance, load balancer, mail gateway, or embedded management plane that still advertises RC4 on a reachable TLS listener, regardless of vendor, version, or operating system.

Tenable's MEDIUM label is already restrained compared with the newer CISA-ADP CVSS 3.1 10.0, and reality says even MEDIUM is still a bit generous for most enterprise environments in 2026. The decisive friction is that the attacker usually needs a legacy client willing to negotiate RC4, plus a traffic-capture position and enough repeated ciphertext to recover useful plaintext; modern browsers and current TLS libraries largely removed RC4 years ago, and modern OpenSSL does not even build RC4 TLS suites by default.

Why this verdict

• Requires the wrong kind of traffic: an attacker usually needs RC4 to be *actually negotiated*, not merely offered, which implies a legacy client or legacy integration path still exists.
• Usually implies on-path or traffic-visibility position: this is not a clean unauthenticated remote server takeover; it is mostly a ciphertext collection and plaintext recovery problem.
• Impact is narrower than the scary labels imply: the practical outcome is typically confidentiality loss or session theft, not arbitrary code execution or domain-wide blast radius.
• Modern defaults already suppress it: RFC 7465 banned RC4 in TLS in 2015, Mozilla deprecated it, and modern OpenSSL no longer builds RC4 TLS suites by default, which slashes the reachable/exploitable population.

Why not higher?

It is not MEDIUM or HIGH in 2026 patch triage terms because the chain stacks multiple frictions: reachable TLS listener, RC4 still enabled, legacy client still willing to use it, enough repeated ciphertext, and attacker visibility of that traffic. That is a lot of compounding reality between 'server offers RC4' and 'attacker gets something useful.'

Why not lower?

It is not IGNORE because the underlying weakness is real, standards bodies prohibited RC4 years ago, and the finding still matters on public-facing legacy portals, management interfaces, and regulated environments. If you still have RC4 enabled anywhere important, you are carrying avoidable confidentiality and compliance debt.

1. Disable RC4 suites — Remove RC4 from server-side cipher lists on web servers, mail gateways, load balancers, appliances, and management planes. For a LOW verdict there is no mitigation SLA; treat this as backlog hygiene and clear it during your normal TLS hardening cycle.
2. Prioritize internet-facing and admin surfaces — Start with public HTTPS, VPN portals, SSO, webmail, and device admin UIs because those are the few places where legacy client negotiation plus attacker visibility can still line up. There is no formal LOW mitigation deadline, so fold this into standard config remediation rather than emergency change windows.
3. Hunt for real RC4 negotiation — Pull load balancer, reverse proxy, Schannel, Java, or OpenSSL handshake logs to confirm whether RC4 is merely advertised or actually negotiated by any client population. If you see real RC4 handshakes, raise the local priority even if the generic verdict stays LOW.
4. Ring-fence legacy exceptions — If a vendor appliance or brittle integration still requires RC4, isolate it behind source allowlists, VPN-only reachability, or a dedicated reverse proxy that terminates with modern ciphers outward. Keep the exception documented because this is legacy debt, not a valid modern baseline.

Run this from an auditor workstation or any Linux jump host that can reach the target service. Invoke it as ./check_rc4.sh example.com 443; no elevated privileges are needed, but nmap gives the cleanest result and openssl is used as a fallback.

#!/usr/bin/env bash
# check_rc4.sh
# Detect whether a remote TLS service still accepts RC4 cipher suites.
# خروج codes:
#   0 = PATCHED
#   1 = VULNERABLE
#   2 = UNKNOWN / usage / dependency issue

set -u

HOST="${1:-}"
PORT="${2:-443}"

if [[ -z "$HOST" ]]; then
  echo "Usage: $0 <host> [port]"
  echo "UNKNOWN"
  exit 2
fi

run_with_timeout() {
  if command -v timeout >/dev/null 2>&1; then
    timeout 12 "$@"
  else
    "$@"
  fi
}

check_with_nmap() {
  if ! command -v nmap >/dev/null 2>&1; then
    return 2
  fi

  local out
  out="$(run_with_timeout nmap -Pn -p "$PORT" --script ssl-enum-ciphers "$HOST" 2>/dev/null)" || return 2

  if echo "$out" | grep -Eiq '\bRC4\b'; then
    echo "VULNERABLE"
    return 1
  fi

  if echo "$out" | grep -Eiq 'ssl-enum-ciphers|TLS'; then
    echo "PATCHED"
    return 0
  fi

  return 2
}

check_with_openssl() {
  if ! command -v openssl >/dev/null 2>&1; then
    return 2
  fi

  local rc4_ciphers
  rc4_ciphers="$(openssl ciphers -v 'ALL:@SECLEVEL=0' 2>/dev/null | awk '/RC4/ {print $1}')"

  if [[ -z "$rc4_ciphers" ]]; then
    # Modern OpenSSL often ships without RC4 TLS suites, so we cannot probe directly.
    return 2
  fi

  local proto cipher out
  for proto in -tls1 -tls1_1 -tls1_2; do
    for cipher in $rc4_ciphers; do
      out="$(printf '' | run_with_timeout openssl s_client -connect "${HOST}:${PORT}" "$proto" -cipher "$cipher" 2>/dev/null)"
      if echo "$out" | grep -Eq 'Cipher is ' && ! echo "$out" | grep -Eiq 'Cipher is \(NONE\)|handshake failure|no cipher match|no shared cipher|alert handshake failure'; then
        echo "VULNERABLE"
        return 1
      fi
    done
  done

  echo "PATCHED"
  return 0
}

if check_with_nmap; then
  exit 0
else
  rc=$?
  if [[ $rc -eq 1 ]]; then
    exit 1
  fi
fi

if check_with_openssl; then
  exit 0
else
  rc=$?
  if [[ $rc -eq 1 ]]; then
    exit 1
  fi
fi

echo "UNKNOWN"
exit 2

Sources

1. Tenable Nessus Plugin 65821
2. RFC 7465 - Prohibiting RC4 Cipher Suites
3. NVD CVE-2015-2808
4. Black Hat Asia 2015 - Bar Mitzvah Attack paper
5. USENIX Security 2013 - On the Security of RC4 in TLS
6. OpenSSL ciphers documentation
7. OWASP Transport Layer Protection Cheat Sheet
8. CISA Known Exploited Vulnerabilities Catalog