CVE intelligence and bounded remediation

CVE-2021-20042 — An unauthenticated remote attacker can use SMA 100 as an unintended proxy or intermediary undetectable proxy to bypass firewall rules

Critical CVSS 9.8

An unauthenticated remote attacker can use SMA 100 as an unintended proxy or intermediary undetectable proxy to bypass firewall rules. This vulnerability affected SMA 200, 210, 400, 410 and 500v appliances.

Severity
Critical
CVSS
9.8 (3.1)
Published
2021-12-08
CISA KEV
Not currently listed
Ecosystem
operating-system
Weaknesses
CWE-441

Affected products

  • sonicwall / sma_200_firmware / 9.0.0.11-31sv
  • sonicwall / sma_200_firmware / 10.2.0.8-37sv
  • sonicwall / sma_200_firmware / 10.2.1.1-19sv
  • sonicwall / sma_210_firmware / 9.0.0.11-31sv
  • sonicwall / sma_210_firmware / 10.2.0.8-37sv
  • sonicwall / sma_210_firmware / 10.2.1.1-19sv

Showing 6 representative product identities from 15 source matches. Confirm exact affected versions with the linked vendor and NVD evidence.

Matched remediation archetype

Server-side request forgery and unintended proxying

This catalog composition supplies bounded fallback guidance. Explicitly reviewed curated workflows load with the complete record below.

Check exposure

  • Inventory server-side URL fetchers, webhooks, importers, previews, redirects, proxies, and protocol handlers reachable from untrusted input.
  • Map egress paths to internal services, metadata endpoints, loopback, private address space, and privileged control planes.
  • Review DNS resolution, redirect, proxy, credential-forwarding, and URL parsing behavior without requesting sensitive targets.

Remediate safely

  • Replace arbitrary destinations with named integrations or a strict allowlist of schemes, hosts, ports, and paths.
  • Resolve and validate every destination and redirect hop, then enforce egress policy independently of application checks.
  • Remove ambient credentials and sensitive headers from fetchers; apply response size, time, and content limits.

Authoritative sources

Complete CVE record and remediation plan

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