How severe is CVE-2021-20042?

CVE-2021-20042 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-20042 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (84th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-20042?

CVE-2021-20042 primarily affects Sonicwall Sma 200 Firmware. In total, 15 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-20042?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2021-20042 published?

CVE-2021-20042 was published on 2021-12-08 and last updated on 2026-06-17.

CVE-2021-20042

CVE-2021-20042 is a critical-severity vulnerability in Sonicwall Sma 200 Firmware with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-441.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 3% (84th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-441
Affected product: Sonicwall Sma 200 Firmware
Published: 2021-12-08
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2021-20042?: 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.
How severe is CVE-2021-20042?: CVE-2021-20042 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-20042 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 3% (84th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-20042?: CVE-2021-20042 primarily affects Sonicwall Sma 200 Firmware. In total, 15 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-20042?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-20042 published?: CVE-2021-20042 was published on 2021-12-08 and last updated on 2026-06-17.

References

https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0026

Affected products (15)

cpe:2.3:o:sonicwall:sma_200_firmware:9.0.0.11-31sv:*:*:*:*:*:*:*
cpe:2.3:o:sonicwall:sma_200_firmware:10.2.0.8-37sv:*:*:*:*:*:*:*
cpe:2.3:o:sonicwall:sma_200_firmware:10.2.1.1-19sv:*:*:*:*:*:*:*
cpe:2.3:o:sonicwall:sma_210_firmware:9.0.0.11-31sv:*:*:*:*:*:*:*
cpe:2.3:o:sonicwall:sma_210_firmware:10.2.0.8-37sv:*:*:*:*:*:*:*
cpe:2.3:o:sonicwall:sma_210_firmware:10.2.1.1-19sv:*:*:*:*:*:*:*
cpe:2.3:o:sonicwall:sma_410_firmware:9.0.0.11-31sv:*:*:*:*:*:*:*
cpe:2.3:o:sonicwall:sma_410_firmware:10.2.0.8-37sv:*:*:*:*:*:*:*
cpe:2.3:o:sonicwall:sma_410_firmware:10.2.1.1-19sv:*:*:*:*:*:*:*
cpe:2.3:o:sonicwall:sma_400_firmware:9.0.0.11-31sv:*:*:*:*:*:*:*
cpe:2.3:o:sonicwall:sma_400_firmware:10.2.0.8-37sv:*:*:*:*:*:*:*
cpe:2.3:o:sonicwall:sma_400_firmware:10.2.1.1-19sv:*:*:*:*:*:*:*
cpe:2.3:o:sonicwall:sma_500v_firmware:9.0.0.11-31sv:*:*:*:*:*:*:*
cpe:2.3:o:sonicwall:sma_500v_firmware:10.2.0.8-37sv:*:*:*:*:*:*:*
cpe:2.3:o:sonicwall:sma_500v_firmware:10.2.1.1-19sv:*:*:*:*:*:*:*

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