PCI DSS Compliance : Scan Interference

Tenable plugin 108714 is not a CVE and not a software flaw. It fires when the scanner detects that something interfered with its PCI DSS ASV scan — an IPS dropping probes, a WAF rate-limiting requests, host-based protection blackholing the scanner IP, a load balancer returning canned responses, or simply too many TCP resets. The plugin flags the scan as unreliable for PCI DSS attestation purposes under PCI DSS requirement 11.3 / ASV Program Guide §7.7. There is no affected version range — it applies to any in-scope cardholder-data-environment (CDE) host where the scanner's traffic was disturbed.

Tenable's HIGH label is calibrated to the PCI auditor, not to a defender's vulnerability backlog. From an ASV's perspective HIGH is correct: a scan with interference cannot be submitted as a passing PCI report, so the QSA will reject the attestation. From a patch-management perspective the label is misleading — there is nothing to patch. The real question is whether your protective controls need a documented scanner allowlist, and whether your CDE segmentation is hiding hosts you legally owe the ASV visibility into.

Why this verdict

• No vulnerability, no exploit path: there is nothing on the affected host that an attacker can leverage. The finding is a *scanner-side* observation about its own visibility.
• PCI workflow impact is real but bounded: a rejected ASV report blocks compliance attestation, which has commercial consequences (fines, brand penalties) but no security consequence. Cost of remediation is reconfiguration, not patching.
• Role multiplier — CDE-scoped perimeter: the affected component is, by definition, the CDE perimeter; if interference is masking an actual exploitable CVE on a cardholder-data system the blast radius is regulated data exposure. This is what keeps the verdict at MEDIUM rather than LOW — you cannot prove the scan would have come back clean.
• Friction audit: zero exploit prerequisites because there is no exploit. The 'attack' is paperwork rejection, fully reversible by allowlisting the Tenable ASV IP ranges and re-running the scan.
• Installed-base context: this plugin fires on a large share of PCI ASV scans on first run; it is a *configuration hygiene* finding, not a rare critical defect.

Why not higher?

A HIGH verdict would imply real attacker leverage; there is none. Tenable's HIGH rating reflects PCI submission risk under the ASV Program Guide, which is an audit construct, not a security one. Vulnerability-management programs that auto-route HIGH findings to emergency-patch pipelines will burn cycles on a paperwork problem.

Why not lower?

LOW or IGNORE would be wrong because the finding invalidates your compliance posture until resolved, and worse, it can *mask* a genuinely exploitable CVE behind the interference — you don't know what the scanner couldn't see. Until re-scanned cleanly you cannot rule out hidden CRITICAL findings on CDE hosts.

1. Allowlist Tenable ASV scanner source IPs end-to-end — Publish the current Tenable Cloud Sensor / PCI ASV IP ranges (see Tenable docs tenable.com/scanner-ip-addresses) to every inline control between the internet and the CDE — edge router ACL, WAF allowlist, IPS exception, host firewall, CDN/Cloudflare rule, rate limiter. The MEDIUM verdict carries no noisgate mitigation SLA, but practically complete this within the next PCI scan window so the attestation can re-submit.
2. Document the allowlist in your PCI scope document — QSAs require evidence that the allowlist exists only for the ASV and does not weaken production protection. Include source IPs, expiry, change-control ticket, and the compensating monitoring control (e.g., SIEM rule alerting on non-Tenable traffic from those ranges).
3. Re-run the PCI ASV scan and verify plugin 108714 is silent — Confirm the next scan returns a clean Plugin 108714 status before submitting to the ASV portal. Compare host counts and open-port counts between the interfered and clean scans — large deltas indicate the original scan was hiding real findings.
4. Triage any new findings revealed by the clean re-scan — This is where the actual security work hides. Treat the delta between blocked and clean scan as a freshly discovered backlog and reassess each new CVE on its own merits.

Run on the auditor / scanner-ops workstation (not the target host) to confirm whether the published Tenable ASV scanner IPs can reach a CDE-scoped target on the expected PCI ports without being rate-limited or filtered. Requires curl, nmap, and outbound network egress. Invoke as ./check_108714.sh <target-host-or-ip>.

#!/usr/bin/env bash
# noisgate verification for Tenable plugin 108714 (PCI DSS Scan Interference)
# Purpose: confirm whether an inline control is dropping/rate-limiting
# scanner-class traffic against a CDE target.
# Exit codes: 0=PATCHED (no interference), 1=VULNERABLE (interference detected), 2=UNKNOWN
set -u
TARGET="${1:-}"
if [ -z "$TARGET" ]; then
  echo "usage: $0 <target-host-or-ip>" >&2
  exit 2
fi

for bin in curl nmap awk grep; do
  command -v "$bin" >/dev/null 2>&1 || { echo "missing dependency: $bin" >&2; exit 2; }
done

PORTS="80,443,8080,8443"
INTERFERENCE=0
REASONS=()

# 1. TCP-connect scan, look for filtered/reset patterns
NMAP_OUT=$(nmap -Pn -sT -p "$PORTS" --reason --max-retries 1 --host-timeout 60s "$TARGET" 2>/dev/null)
echo "$NMAP_OUT" | grep -Eq 'filtered|reset' && {
  INTERFERENCE=1
  REASONS+=("nmap reports filtered/reset on PCI ports")
}

# 2. Banner / response consistency over 10 rapid HTTPS requests
CODES=()
for i in $(seq 1 10); do
  C=$(curl -ksS -o /dev/null -w '%{http_code}' --max-time 5 "https://$TARGET/" 2>/dev/null || echo "000")
  CODES+=("$C")
done
UNIQ=$(printf '%s\n' "${CODES[@]}" | sort -u | wc -l)
LAST=${CODES[9]}
FIRST=${CODES[0]}
if [ "$UNIQ" -gt 2 ] || { [ "$FIRST" != "000" ] && [ "$LAST" = "000" ]; }; then
  INTERFERENCE=1
  REASONS+=("HTTPS response codes drift across rapid requests: ${CODES[*]}")
fi

# 3. Look for WAF / CDN block signatures
BODY=$(curl -ksS --max-time 5 -A "Mozilla/5.0 (compatible; Nessus)" "https://$TARGET/" 2>/dev/null || true)
if echo "$BODY" | grep -Eiq 'cloudflare|akamai|ray id|access denied|request blocked|attention required'; then
  INTERFERENCE=1
  REASONS+=("WAF / CDN block page returned to scanner-class User-Agent")
fi

if [ "$INTERFERENCE" -eq 1 ]; then
  echo "VULNERABLE: scan interference detected against $TARGET"
  for r in "${REASONS[@]}"; do echo " - $r"; done
  exit 1
fi

echo "PATCHED: no scan interference signature detected against $TARGET"
exit 0

Sources

1. Tenable plugin 108714 detail
2. Tenable scanner IP addresses (for allowlisting)
3. PCI SSC ASV Program Guide
4. PCI DSS v4.0 Requirement 11.3 (vulnerability scans)
5. Tenable: configuring PCI ASV scans
6. Tenable community: interference troubleshooting
7. CISA KEV catalog (for confirming non-listing)