OpenSSL 1

Tenable plugin 152782 covers two August 2021 OpenSSL flaws — CVE-2021-3711 (SM2 decryption buffer overflow, up to 62 bytes attacker-controlled) and CVE-2021-3712 (ASN.1 string out-of-bounds read, info-disclosure / DoS). Both affect OpenSSL 1.1.1 through 1.1.1k, plus the 1.0.2 branch up through 1.0.2y (premium support only). Fix lands in 1.1.1l / 1.0.2za, with distro backports in RHEL, Ubuntu, SUSE, and Debian shipped within days of the upstream advisory.

Vendor-aggregated severity is HIGH with NVD scoring 3711 at 9.8, and that number is what drives plugin 152782's noise. It does not survive contact with reality. CVE-2021-3711 only triggers in code paths that call EVP_PKEY_decrypt() on SM2 ciphertext from an attacker-controlled source — SM2 is the PRC national crypto standard and is essentially absent from Western web stacks, mail stacks, VPN stacks, and TLS terminators. CVE-2021-3712 needs an app that prints/processes ASN.1 strings from an attacker-supplied cert without using the safe accessors. Real-world exploitation: zero confirmed, not on CISA KEV, EPSS percentile floor.

Why this verdict

• SM2 path is dead code in Western stacks — CVE-2021-3711's 9.8 assumes a generic memcpy overflow, but the SM2 decryption call site does not exist in nginx, Apache, postfix, dovecot, OpenVPN, strongSwan, curl, or any default OS-shipped TLS termination, so reachable population is a tiny fraction of the ~2M+ banner-matching hosts.
• ASN.1 leak is bounded and probabilistic — CVE-2021-3712 yields ≤1 page of adjacent heap, not chosen-address read; reliable secret extraction requires mutual-TLS or S/MIME parsing in a long-lived process with predictable allocator layout.
• Five years, zero KEV, EPSS bottom-quartile — no campaign, no PoC weaponization, no ransomware affiliate has built tooling, despite OpenSSL being one of the most-watched libraries on earth.
• Role multiplier — TLS terminator / API gateway: The chain does not succeed. Default builds do not enable SM2; ASN.1 leak yields adjacent-heap bytes, not the server private key, with overwhelming probability.
• Role multiplier — identity provider / PKI CA: ADCS, HashiCorp Vault PKI, smallstep, ADFS — none link against affected OpenSSL 1.1.1 SM2 paths; these stacks use Windows CNG or Go crypto, so the floor-raising role does not apply.
• Role multiplier — VPN / network edge: FortiGate, PAN-OS, ASA, BIG-IP ship their own crypto builds and patched within their vendor cycles; even where 1.1.1 ≤ k is present, SM2 is not compiled in.
• Role multiplier — embedded / IoT firmware: This is where most unpatched OpenSSL 1.1.1 ≤ k actually lives. Impact ceiling is device DoS or limited heap-leak from a TLS handshake, *not* fleet pivot — still MEDIUM, not HIGH.

Why not higher?

HIGH would require either (a) confirmed reachability in a default mainstream TLS stack, or (b) public weaponized PoC, or (c) KEV listing. None of those exist. The 9.8 NVD score scores the worst theoretical primitive, not the realistic exploit chain.

Why not lower?

LOW / IGNORE would require the bug to be unreachable everywhere. CVE-2021-3712 *is* reachable on any process that does mTLS with permissive cert printing — that's a non-zero population (zero-trust gateways, B2B APIs, OCSP responders, S/MIME-handling mail servers). MEDIUM keeps it on the patch backlog rather than the daily-emergency queue.

1. Patch via OS package channel — All maintained distros backported the fix within days of August 2021 disclosure. Run yum update openssl / apt upgrade openssl / zypper update openssl across the fleet — this is the cheapest control. Within MEDIUM, no mitigation SLA applies; ride this into the standard 365-day noisgate remediation SLA window.
2. Inventory SM2 usage explicitly — Grep build flags and binaries for SM2 symbol usage (nm -D libssl.so.1.1 | grep -i sm2, objdump -T … | grep SM2). If zero hits, CVE-2021-3711 is unreachable in your environment and you can deprioritize the 9.8 component of this plugin entirely.
3. Audit mTLS-accepting services for cert-name printing — Check API gateways, OCSP responders, S/MIME mail relays for use of legacy X509_NAME_oneline() or X509_get1_email(). Migrating to X509_NAME_print_ex() neutralizes CVE-2021-3712 even on unpatched OpenSSL.
4. Restart long-lived TLS processes after package update — yum update openssl does not restart linked processes. Use needs-restarting -r (RHEL), checkrestart (Debian), or lsof | grep libssl to find lingering vulnerable processes. Without restart, the patch is dormant on disk.
5. Schedule replacement of OpenSSL 1.1.1 entirely — 1.1.1 went end of life on 2023-09-11. If you are still seeing 152782 in 2026, you are running EOL crypto. Move to OpenSSL 3.0 LTS or 3.2 within the noisgate remediation SLA of 365 days.

Run this on each target Linux host as root or via your config-mgmt agent (Ansible become: true, Salt state.apply). Invoke as sudo ./check-openssl-1.1.1l.sh. It checks the system OpenSSL binary version and library, and reports whether SM2 support is even compiled in.

#!/usr/bin/env bash
# noisgate verification — Tenable 152782 / CVE-2021-3711 + CVE-2021-3712
# Output: VULNERABLE | PATCHED | UNKNOWN
set -u

VULN=0
PATCHED=0
NOTE=""

# 1) Locate openssl binary
OSSL=$(command -v openssl || true)
if [[ -z "$OSSL" ]]; then
  echo "UNKNOWN: openssl binary not found on PATH"
  exit 2
fi

VER=$($OSSL version 2>/dev/null | awk '{print $2}')
echo "openssl reports: $VER"

# 2) Version comparison — only the 1.1.1 branch is in scope for this plugin
case "$VER" in
  1.1.1[a-k]|1.1.1)
    VULN=1
    NOTE="upstream 1.1.1<=k"
    ;;
  1.1.1[l-z]*|1.1.1[l-z])
    PATCHED=1
    NOTE="upstream >=1.1.1l"
    ;;
  3.*|1.0.2*)
    NOTE="out of plugin 152782 scope ($VER)"
    ;;
  *)
    NOTE="unrecognized version string"
    ;;
esac

# 3) Distro backport check — RHEL/CentOS
if command -v rpm >/dev/null 2>&1; then
  RPMVER=$(rpm -q --qf '%{VERSION}-%{RELEASE}\n' openssl-libs 2>/dev/null | head -1)
  echo "rpm openssl-libs: $RPMVER"
  # RHEL8 fixed in 1.1.1k-5.el8_5 ; RHEL7 fixed in 1.0.2k-22.el7_9
  if [[ "$RPMVER" =~ ^1\.1\.1k-[5-9] ]] || [[ "$RPMVER" =~ ^1\.1\.1k-[1-9][0-9] ]]; then
    PATCHED=1; VULN=0; NOTE="RHEL backport applied"
  fi
fi

# 4) Distro backport check — Debian/Ubuntu
if command -v dpkg-query >/dev/null 2>&1; then
  DEBVER=$(dpkg-query -W -f='${Version}\n' libssl1.1 2>/dev/null | head -1)
  echo "dpkg libssl1.1: $DEBVER"
fi

# 5) SM2 reachability check (CVE-2021-3711 only matters if SM2 linked)
LIBSSL=$(ldconfig -p 2>/dev/null | awk '/libcrypto.so.1.1/ {print $4; exit}')
if [[ -n "$LIBSSL" ]] && command -v nm >/dev/null 2>&1; then
  if nm -D "$LIBSSL" 2>/dev/null | grep -qi 'SM2\|sm2_'; then
    echo "SM2 symbols present in $LIBSSL — CVE-2021-3711 path is REACHABLE"
  else
    echo "SM2 symbols absent — CVE-2021-3711 path NOT reachable on this host"
  fi
fi

if (( PATCHED == 1 )); then
  echo "PATCHED ($NOTE)"; exit 0
elif (( VULN == 1 )); then
  echo "VULNERABLE ($NOTE)"; exit 1
else
  echo "UNKNOWN ($NOTE)"; exit 2
fi

Sources

1. Tenable plugin 152782
2. OpenSSL Security Advisory 2021-08-24
3. OpenSSL vulnerabilities index
4. NVD — CVE-2021-3711
5. NVD — CVE-2021-3712
6. Debian security tracker — CVE-2021-3711
7. Wiz vulnerability writeup — CVE-2021-3711
8. CISA KEV catalog (verify not listed)