CVE-2021-20035

CVE-2021-20035 is an OS command injection flaw (CWE-78) caused by improper neutralization of special elements in the management interface of SonicWall SMA100 series appliances. A remote attacker who has authenticated with low-level privileges can inject arbitrary operating system commands, which are executed on the appliance as the 'nobody' user. Per the CVSS scoring, the primary impact is on availability, potentially leading to denial of service, though command execution on the appliance could facilitate further abuse. The flaw affects SMA 200, 210, 400, 410, and 500v firmware. CISA added it to the Known Exploited Vulnerabilities catalog on 2025-04-16, and related reporting describes ongoing attacks against SonicWall SMA 100 devices — including by threat group UNC6148 deploying the OVERSTEP rootkit and tailored backdoor malware, some against fully patched appliances — so defenders should treat this as actively exploited.

What to do: Patch to the fixed firmware release specified in the SonicWall advisory for your SMA model as soon as possible; federal agencies must follow the BOD 22-01 mitigation deadline per the CISA KEV required action. Restrict the management interface to trusted networks, enforce MFA on the portal, and hunt for signs of compromise such as the OVERSTEP rootkit, unexpected persistence, or unfamiliar accounts, since reporting indicates tailored backdoor malware in recent SMA 100 attacks.