Google finds custom backdoor being installed on SonicWall network devices

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.

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.

SonicWall SMA 100 series secure remote-access appliances contain an unauthenticated stack-based buffer overflow (CWE-121) in the appliance's network-facing interface, triggered by crafted requests sent to the device without any credentials. A remote attacker who triggers the overflow can execute arbitrary code on the appliance with the privileges of the affected service, gaining a foothold on an internet-facing VPN gateway that typically sits at the network edge. Any organization running an SMA 100 series appliance is affected, and because these appliances provide remote access to corporate networks, compromise can expose entire internal environments. Exploitation is confirmed in the wild: the flaw was added to CISA KEV on 2022-01-28 with known ransomware use, and EPSS assigns a 99.9% probability of exploitation within 30 days (100th percentile). No public proof-of-concept is catalogued in the provided data, but the KEV listing and EPSS score indicate active attacker interest.

Do: Upgrade SMA 100 series appliances to firmware 10.0.7.2 or later per SonicWall's instructions, as required by the CISA KEV listing. Until patched, restrict internet exposure of the SMA portal and management interface to trusted sources where feasible. Because ransomware operators are known to exploit this flaw, review appliance logs for signs of compromise and monitor for unexpected account creation or traffic after patching.

Improper neutralization of special elements in the SMA100 management interface '/cgi-bin/viewcert' POST http method allows a remote authenticated attacker to inject arbitrary commands as a 'nobody' user. This vulnerability affected SMA 200, 210, 400, 410 and 500v appliances.

CVE-2024-38475 is an improper escaping of output flaw (CWE-116) in the mod_rewrite module of the Apache HTTP Server. It is triggered when mod_rewrite maps a request URL to a filesystem location and mishandles encoded characters, allowing a crafted request to reach files that the server is permitted to serve but that were never intentionally or directly reachable by any URL. An attacker can abuse this to disclose source code (for example, serving raw application files) or, depending on the server's configuration and handlers, achieve code execution. Any Apache HTTP Server deployment that uses mod_rewrite is potentially affected; the source data does not specify the vulnerable version range. The flaw was added to CISA's Known Exploited Vulnerabilities catalog on 2025-05-01, confirming exploitation in the wild, and EPSS assigns it a 100% probability of exploitation within 30 days (100th percentile), though no public proof-of-concept is known and ransomware use is unconfirmed.

Do: Inventory Apache HTTP Server deployments, prioritize internet-facing ones, and check whether mod_rewrite is in use (RewriteRule directives in server config, virtual hosts, or .htaccess files); upgrade to the vendor's fixed release, 2.4.60 or later. If immediate upgrade is not possible, follow vendor guidance to harden or constrain mod_rewrite rules, and treat the issue as actively exploited per CISA KEV, applying BOD 22-01 mitigations for cloud service usage or discontinuing use if mitigation is unavailable.

A vulnerability in SMA100 allows a remote authenticated attacker with SSLVPN user privileges to bypass the path traversal checks and delete an arbitrary file potentially resulting in a reboot to factory default settings.