CVE-2021-20035
CVE-2021-20035 is a security flaw in SonicWall SMA100 Appliances, SonicWall’s firewall and remote-access equipment. Someone who already has a way in can use SonicWall SMA100 Appliances to run their own code. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 16 Apr 2025.[1]
SonicWall SMA100 Appliances is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. SonicWall has published a fix or advice.
Description
CISA calls it an OS command injection in SonicWall SMA100 Appliances. In its words: “SonicWall SMA100 appliances contain an OS command injection vulnerability in the management interface that allows a remote authenticated attacker to inject arbitrary commands as a 'nobody' user, which could potentially lead to code execution.”[1]
The underlying weakness is OS command injection (CWE-78), in MITRE’s list of common software weaknesses.[2]
It scores 6.5 out of 10 on the Common Vulnerability Scoring System, which rates it medium, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; SonicWall’s advisory has them[3]. CISA names the product as SonicWall SMA100 Appliances.
Most families won’t have SonicWall SMA100 Appliances; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 16 Apr 2025, 1,297 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 7 May 2025 to fix it.[1]
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 4%. That’s in the top 9% of the flaws it scores.[4]
CISA assesses it as not automatable: each attack takes some work.
CISA doesn’t say who was attacked, or how.
Fix
SonicWall has published a fix or advice.[3] CISA’s required action: “Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.”[1]
- Check whether you use it.SonicWall SMA100 Appliances is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed, or not in use. CISA gave US government agencies until 7 May 2025 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 6.5.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 4%.[4] |
See also
Other SonicWall SMA100 Appliances flaws
- CVE-2023-44221: OS command injection ·
Other SonicWall flaws
- CVE-2026-83549, SonicWall SMA1000 Appliances: OS command injection ·
- CVE-2026-83548, SonicWall SMA1000 Appliances: server-side request forgery ·
- CVE-2026-15410, SonicWall SMA1000 Appliances: code injection ·
- CVE-2026-15409, SonicWall SMA1000 Appliances: server-side request forgery ·
- CVE-2025-40602, SonicWall SMA1000 appliance: sMA1000 missing authorization ·
Other OS command injection flaws
- CVE-2026-110447, Collabora Online – Built-in CODE Server: online – built-in CODE server OS command injection ·
- CVE-2026-106931, EG Secure Solutions SiteGuard Server Edition: OS command injection ·
- CVE-2026-49869, Kestra OSS: OSS OS command injection ·
- CVE-2026-73570, Synacor Zimbra Collaboration Suite (ZCS): OS command injection ·
- CVE-2026-16812, Arista VeloCloud Orchestrator: on-prem OS command injection ·
Every SonicWall flaw on CISA’s list · Everything added in April 2025
References
- ^ Cybersecurity and Infrastructure Security Agency. “SonicWall SMA100 Appliances OS Command Injection Vulnerability”. Known Exploited Vulnerabilities Catalog, added 16 Apr 2025.
- ^ National Institute of Standards and Technology. “CVE-2021-20035 Detail”. National Vulnerability Database, published 27 Sep 2021.
- ^ SonicWall. Advisories and fixes: psirt.global.sonicwall.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.044, percentile 91.3, 31 Oct 2026.
- CVE Program. “CVE-2021-20035”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.