SonicWall SMA100 Appliances OS Command Injection Vulnerability (CVE-2021-20035)
Published In CISA KEV since Sources: CVE.org, pwn.watch
What is affected, what to do
Improper neutralization of special elements in the SMA100 management interface allows a remote authenticated attacker to inject arbitrary commands as a 'nobody' user which potentially leads to DoS.
The vulnerability is being actively exploited; treat it as a priority. Update sma_500v to version 9.0.0.11-31sv. Immediate actions, mitigation and detection rules are in the runbook below.
- Affected
- SonicWall SMA100
eq 9.0.0.10-28sv and earlier..9.0.0.10-28sv and earlier - SonicWall SMA100
eq 10.2.0.7-34sv and earlier..10.2.0.7-34sv and earlier - SonicWall SMA100
eq 10.2.1.0-17sv and earlier..10.2.1.0-17sv and earlier
- SonicWall SMA100
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Metrics
6.5
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: NVD, CVSS v3
6.5
CVSS v3
Severity Medium on the scale from 0 to 10.
Source: CVE.org, pwn.watch
4.4 %
EPSS score
Moderate — model estimates 1-10% exploitation likelihood.
Source: FIRST EPSS, percentile 91.3
Show all metrics
- Severity
- Critical
Priority (0–325)
The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?
Read in glossary- 199.16 Methodology
Exploit maturity
An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.
Read in glossary- actively exploited
XIEM Effective CVSS
XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.
Read in glossary- 6.5 Methodology
CVSS v3
CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.
Read in glossary- 6.5
EPSS score
The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.
Read in glossary- 4.4 %
- Moderate — model estimates 1-10% exploitation likelihood.
EPSS percentile
The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.
Read in glossary- 91.3
- Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
KEV status
The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.
Read in glossary- Actively exploited
- Published
In CISA KEV since
The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.
Read in glossaryCWE
CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.
Read in glossary- CWE-78
Response and mitigation
Why act now?
Prioritisation rationale
This flaw is reachable over the network with low complexity but requires valid credentials. Its KEV listing shows attackers are pairing it with stolen or weak credentials to execute commands on edge appliances. The original DoS-only framing was revised to reflect potential code execution. Typical targets are remote-access gateways at mid-market and critical-infrastructure organisations, which attackers use as a beachhead into internal networks and a source of further credentials. Exploitation likelihood is well above average. Treat it as critical with a 24-hour deadline if the management interface is internet-facing or MFA is missing. If management is strictly segmented and MFA is enforced, patching in the regular emergency change window is defensible.
Runbook step 1
Immediate response (0-24 h)
- Inventory every SonicWall SMA100 appliance (including SMA 200/210) and its firmware. Affected builds are 9.0.0.10-28sv and earlier, 10.2.0.7-34sv and earlier, and 10.2.1.0-17sv and earlier.
- Upgrade each release train to its fixed build: 9.0.0.11-31sv, 10.2.0.8-37sv or 10.2.1.1-19sv. For other SMA100 models, look up the matching version in the vendor advisory. If you are on an unsupported 9.x train, plan the move to a maintained 10.2 build.
- Block the HTTPS management interface from the internet and from user VLANs now. Allow only dedicated admin jump hosts.
- Exploitation requires authentication, so rotate all local admin and user passwords on the appliance. Eliminate default credentials and enforce MFA/TOTP for admin and VPN logins. Also rotate any LDAP/RADIUS service accounts bound to the appliance.
- Before upgrading, export appliance logs and configuration to preserve forensic evidence. Then review them for unknown accounts, modified bookmarks, portal customisations and unexplained reboots.
- If you suspect compromise, upgrading alone is not enough. Factory-reset the appliance, reinstall firmware, review the configuration manually, and treat every credential that transited the appliance as compromised.
Runbook step 2
Mitigation layers
- Network segmentation: Expose management only on an out-of-band management VLAN. Add an upstream firewall rule that denies HTTPS management from WAN and client networks and permits only admin jump-host IPs.
- Appliance configuration: Enable the built-in management access restrictions (allowed source IPs/interfaces). Disable HTTP and SSH management on the WAN interface.
- Egress filtering: Restrict appliance-originated traffic to what it needs (DNS, NTP, syslog, licensing/update servers, auth backends). Drop and log everything else so reverse shells and second-stage downloads fail.
- IAM/least privilege: Limit admin roles to named individual accounts and retire shared admin logins. Enable lockout after failed attempts and set short admin session timeouts.
- IPS/WAF: Where inline inspection in front of the appliance is possible, alert or block on management requests whose parameters contain shell metacharacters (
;,|,`,$(,&&). Enable your IPS vendor's signatures for CVE-2021-20035. - Lifecycle: Replace out-of-support appliances with a maintained ZTNA/VPN service. Until then, record the residual risk formally, as NIS2 Art. 21 expects.
Runbook step 3
Detection rules
- Appliance syslog (SIEM): Detect successful admin logins from outside the admin network or at unusual hours. SPL shape:
index=sonicwall sourcetype=sma* "admin" "login" "success" NOT src_ip IN (<admin_jumphosts>) - Web/proxy logs in front of the appliance: Look for management requests containing shell metacharacters or URL-encoded forms such as
%3B,%7C,%60and%24%28. Sigma shape:cs-uri-query|contains: ['%3B','%7C','%60','$(']combined with destination = SMA management IP. - Network telemetry (Zeek/Suricata): Flag new outbound connections initiated by the SMA appliance itself to destinations outside its known services, especially on odd ports or with long-lived sessions. KQL shape:
ZeekConn | where id_orig_h == "<sma_ip>" and id_resp_h !in (allowlist) - Availability/DoS signal: Watch for unexpected reboots, service crashes or mass VPN session drops. Alert on heartbeat loss and restart messages in syslog.
- Configuration drift: Hash and diff exported configurations on a schedule. Alert on new local accounts, changed authentication servers or new portal bookmarks.
- Appliance syslog (SIEM): Detect successful admin logins from outside the admin network or at unusual hours. SPL shape:
Detection rules
No NEOSEC detection rule is available for this vulnerability yet.
Classification under NIS2 and CRA
Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.
NIS2
NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.
Read in glossary- Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
CRA
The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.
Read in glossary- Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
ISO/IEC 27001
ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.
Read in glossary- Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.
Description
Improper neutralization of special elements in the SMA100 management interface allows a remote authenticated attacker to inject arbitrary commands as a 'nobody' user which potentially leads to DoS.
Source: NVD (NIST), CISA KEV Catalog, CVE.org (MITRE), pwn.watch, cvelistv5
Affected products
The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.
| Affected versions | Fixed in | ||
|---|---|---|---|
| SonicWall | SMA100 |
|
|
| sonicwall | sma_500v |
|
|
Vendors and products
Affected operating systems
| Other | sonicwall | sma_200_firmware | — |
| Other | sonicwall | sma_210_firmware | — |
| Other | sonicwall | sma_400_firmware | — |
| Other | sonicwall | sma_410_firmware | — |
Weakness classes (CWE)
CWE-78Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
Base
The product constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component.
Entry at MITRE CWE-78
Public exploit references
Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.
| CISA KEV Catalog | CISA Known Exploited Vulnerability (opens in a new tab)cisa.gov | actively exploited |
References & sources
- psirt.global.sonicwall.comSonicWall advisory: SonicWall SMA100 Appliancesx_refsource_CONFIRM, Vendor advisory, pwn-watch
- cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2021-20035government-resource, US government resource
- pwn.watchpwn.watch: SonicWall SMA100 Appliances: SMA100 Appliances OS Command Injection Vulnerabilitypwn-watch
- NVD (NIST)NVD: CVE-2021-20035pwn-watch
- cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch
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<a href="https://intel.neosec.eu/en/cve/CVE-2021-20035"><img src="https://intel.neosec.eu/badge/cve/CVE-2021-20035.svg?lang=en" alt="CVE-2021-20035 – NEOSEC Intel" height="20"></a>