CVE-2021-20038
CRITICALCISA KEVEPSS 100th pctlDescription
A Stack-based buffer overflow vulnerability in SMA100 Apache httpd server's mod_cgi module environment variables allows a remote unauthenticated attacker to potentially execute code as a 'nobody' user in the appliance. This vulnerability affected SMA 200, 210, 400, 410 and 500v appliances firmware 10.2.0.8-37sv, 10.2.1.1-19sv, 10.2.1.2-24sv and earlier versions.
How to fix
Actively exploited, no published fix found yet
CISA required action: Apply updates per vendor instructions.
Federal remediation due: 2022-02-11
Known ransomware campaign use
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Exploit Intelligence
Very high risk: more likely to be exploited than 100% of all known CVEs.
SonicWall SMA 100 Appliances Stack-Based Buffer Overflow Vulnerability
SonicWall SMA 100 devies are vulnerable to an unauthenticated stack-based buffer overflow vulnerability where exploitation can result in code execution.
Apply updates per vendor instructions.
Remediation due: 2022-02-11
Associated with ransomware campaigns
References
Related Vulnerabilities
Other CWE-121 (Stack-based Buffer Overflow) vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2025-22457 | Critical | 9.0 | 100% | KEV + Ransom | Fix |
| CVE-2025-0282 | Critical | 9.0 | 100% | KEV + Ransom | - |
| CVE-2009-0927 | High | 8.8 | 97% | KEV | Fix |
| CVE-2020-10924 | High | 8.8 | 87% | - | - |
| CVE-2022-20705 | Critical | 10.0 | 80% | - | - |
| CVE-2016-6563 | Critical | 9.8 | 80% | - | - |
Common questions
How do I fix CVE-2021-20038?
No published fix for CVE-2021-20038 has been found yet. It is on the CISA Known Exploited Vulnerabilities list; federal agencies must remediate by 2022-02-11. Apply the vendor's mitigations per CISA's guidance.
Is CVE-2021-20038 being actively exploited?
Yes. CVE-2021-20038 is listed in the CISA Known Exploited Vulnerabilities catalog, which means exploitation has been observed in the wild. CISA has also linked it to known ransomware campaigns. US federal agencies were required to remediate it by 2022-02-11. Treat it as a priority whatever its CVSS score says.
How severe is CVE-2021-20038?
CVE-2021-20038 has a CVSS v3 base score of 9.8, rated critical. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2025-10-31.