OpenSSL SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG Ciphersuite Di

CVE-2008-7270 / CVE-2010-4180 describe a flaw in OpenSSL's session resumption path: when the SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG compatibility option is enabled, a resumed session can be forced to use a *different* — potentially weaker or explicitly disabled — cipher than the one negotiated in the original handshake. An MITM who observes the initial handshake and poisons the session cache can steer subsequent resumes onto an attacker-chosen ciphersuite. Affected versions are OpenSSL prior to 0.9.8j for the disabled-cipher variant and prior to 0.9.8q / 1.0.0c for the downgrade variant. The offending flag was a legacy hack for ancient Netscape 3.x compatibility.

The vendor MEDIUM label (CVSS2 4.3, AV:N/AC:M/Au:N/C:P/I:N/A:N) is generous for 2026 reality. Modern OpenSSL builds silently ignore this flag, virtually no live web/API/mail server ships with it enabled, TLS 1.3 has entirely different resumption semantics (PSK-based), and the attacker still needs an on-path position to sniff and poison the cache. Tenable's own text notes no known exploits. In a modern enterprise, this plugin firing is almost always noise from a legacy appliance or an unpatched embedded stack — not a live threat.

Why this verdict

• Requires opt-in vulnerable flag: the affected code only runs when SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG is set at runtime — a Netscape 3.x compatibility hack. No modern distro package or web server config enables it.
• On-path MITM prerequisite: attacker must already sit between client and server to sniff the session ID and inject a poisoned resume. That prerequisite alone assumes coffee-shop-tier network conditions, not a hardened enterprise LAN.
• No weaponizable downgrade target in 2026: modern TLS configs strip NULL/EXPORT/RC4 ciphers, so even a successful downgrade lands on AES-GCM or ChaCha20 — nothing to decrypt.
• Role multiplier — web/app server (typical role): chain succeeds only if server is running OpenSSL 0.9.8 <j / <q AND has weak ciphers configured AND MITM is achieved. Blast radius is a single hijacked session's confidentiality. No lateral movement.
• Role multiplier — network edge appliance (high-value role): legacy load balancers or VPN concentrators from 2010-era firmware could theoretically expose this, but modern firmware from F5/Citrix/Cisco has long since fixed the flag handling. No fleet-scale outcome.
• Role multiplier — legacy embedded/OT devices: worst realistic case. Even so, impact is per-session TLS confidentiality on a device that likely has bigger exposures. Does not clear the HIGH floor.
• No KEV, negligible EPSS, no PoC tooling in 15 years — the empirical exploitation rate is essentially zero.
• TLS 1.3 obsoletes the entire class: any endpoint that has moved to TLS 1.3 uses PSK-based resumption and is structurally immune.

Why not higher?

Nothing in the modern threat landscape supports MEDIUM or above. The prerequisites compound: legacy OpenSSL, opt-in compat flag, weak-cipher server config, and an on-path MITM position — with an impact ceiling of one hijacked TLS session's confidentiality. No RCE, no persistence, no privilege gain. This is not a role-multiplier candidate because the flaw sits in a client-facing TLS server, not in identity/PKI/hypervisor infrastructure.

Why not lower?

It is not IGNORE because a genuinely vulnerable stack still enables passive-plus-active decryption of session traffic, which is a real (if narrow) confidentiality violation. On regulated data flows (PCI, HIPAA), even a low-probability decryption path warrants tracking in the vulnerability register and eventual upgrade — hence LOW rather than IGNORE.

1. Retire the affected TLS stack via normal patch/upgrade cadence — Every supported OS shipped a fix by early 2011. If you still see plugin 51893 firing, you have a legacy appliance or unpatched embedded device — schedule its lifecycle replacement. Per noisgate remediation SLA for LOW, treat as backlog hygiene within the 365-day window; there is no mitigation SLA for LOW.
2. Disable weak/legacy ciphersuites server-side — Even if the buggy flag is present, an attacker needs a weak cipher to downgrade *to*. Apply Mozilla intermediate or modern TLS config: TLS 1.2+ AEAD suites only, no NULL/EXPORT/RC4/DES. This eliminates the downgrade target.
3. Force TLS 1.3 where clients support it — TLS 1.3 uses PSK-based resumption and does not honor the vulnerable session cache path. Structural immunity for TLS 1.3-only endpoints.
4. Filter the finding by asset criticality — Suppress this plugin on internal-only, non-regulated endpoints. Keep it live on internet-facing and PCI-scope assets so it doesn't slip into a compliance report.

Run on an auditor workstation with network reach to the target. Requires openssl client (any modern version) and shell. Invoke as ./check-51893.sh <host> <port> — e.g., ./check-51893.sh mail.example.com 443. No privileges needed; this is a remote probe.

#!/usr/bin/env bash
# noisgate check for tenable:51893 / CVE-2008-7270 / CVE-2010-4180
# Probes OpenSSL session-resume behavior for ciphersuite downgrade
set -u

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

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

if ! command -v openssl >/dev/null 2>&1; then
  echo "UNKNOWN: openssl client not installed" >&2
  exit 3
fi

TMP=$(mktemp -d)
trap 'rm -rf "$TMP"' EXIT

# Step 1: pull server's OpenSSL banner (if exposed) and negotiated version
BANNER=$(echo | openssl s_client -connect "$HOST:$PORT" -servername "$HOST" 2>/dev/null | grep -Ei 'openssl|server:' | head -3)

# Step 2: initiate session with a strong cipher, save session
STRONG_CIPHER="ECDHE-RSA-AES256-GCM-SHA384"
openssl s_client -connect "$HOST:$PORT" -servername "$HOST" \
  -cipher "$STRONG_CIPHER" -sess_out "$TMP/sess.pem" \
  -tls1_2 </dev/null >"$TMP/first.log" 2>&1

if [ ! -s "$TMP/sess.pem" ]; then
  echo "UNKNOWN: could not establish TLS 1.2 session with $STRONG_CIPHER"
  exit 3
fi

# Step 3: resume the session but request a WEAKER cipher
WEAK_CIPHERS="NULL-SHA:EXP-RC4-MD5:DES-CBC-SHA:RC4-MD5"
RESUME_OUT=$(openssl s_client -connect "$HOST:$PORT" -servername "$HOST" \
  -cipher "$WEAK_CIPHERS" -sess_in "$TMP/sess.pem" \
  -tls1_2 </dev/null 2>&1)

RESUMED=$(echo "$RESUME_OUT" | grep -c 'Reused')
NEGOTIATED=$(echo "$RESUME_OUT" | grep -E '^\s*Cipher\s*:' | head -1 | awk -F: '{print $2}' | tr -d ' ')

# Interpret
if [ "$RESUMED" -gt 0 ] && [ -n "$NEGOTIATED" ] && [ "$NEGOTIATED" != "$STRONG_CIPHER" ] && [ "$NEGOTIATED" != "0000" ]; then
  echo "VULNERABLE: session resumed on a different cipher ($NEGOTIATED)"
  echo "$BANNER"
  exit 1
fi

# Also flag TLS 1.0/1.1-only servers with old OpenSSL banner as suspect
if echo "$BANNER" | grep -qE 'OpenSSL/0\.9\.[0-7]|OpenSSL/0\.9\.8[a-p]|OpenSSL/1\.0\.0[ab]?'; then
  echo "VULNERABLE: server banner reports OpenSSL version below fix (0.9.8q / 1.0.0c)"
  echo "$BANNER"
  exit 1
fi

echo "PATCHED: session resume did not downgrade cipher and banner (if any) is post-fix"
exit 0

Sources

1. Tenable Plugin 51893
2. NVD — CVE-2010-4180
3. Red Hat — CVE-2010-4180 solution
4. RHSA-2010:0977
5. RHSA-2010:0978
6. RHSA-2010:0979
7. SUSE — CVE-2010-4180
8. Debian Bug #529221 — Netscape/OpenSSL Cipher Forcing Bug