SonicWall Email Security Unrestricted Upload of File Vulnerability (CVE-2021-20022)
Published Last modified In CISA KEV since Sources: SingCERT, CVE.org
- Actively exploited
- Source: CSA/SingCERT How we classify
- Ransomware
What is affected, what to do
SonicWall Email Security version 10.0.9.x contains a vulnerability that allows a post-authenticated attacker to upload an arbitrary file to the remote host.
The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. Update email_security to version 10.0.9.6103, email_security_virtual_appliance to version 10.0.9.6105, hosted_email_security to version 10.0.9.6103. Immediate actions, mitigation and detection rules are in the runbook below.
- Affected
- SonicWall Email Security
eq 10.0.9 and earlier..10.0.9 and earlier
- SonicWall Email Security
Not sure whether and how you are affected? Ask a question about this vulnerability
Metrics
7.2
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: NVD, CVSS v3
7.2
CVSS v3
Severity High on the scale from 0 to 10.
Source: SingCERT, CVE.org
16.6 %
EPSS score
Elevated — model estimates 10-50% exploitation likelihood.
Source: FIRST EPSS, percentile 97.0
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- 236.29 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 exploitedSource: CSA/SingCERT How we classify
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- 7.2 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- 7.2
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- 16.6 %
- Elevated — model estimates 10-50% 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- 97.0
- 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 glossary- CISA assessment (SSVC)
- Exploitation: active · automatable · Technical impact: total
- Source: CISA Vulnrichment, as of 12 August 2026
CWE
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-434
Response and mitigation
Why act now?
Prioritisation rationale
On its own, this flaw requires admin privileges. In the documented chain, however, CVE-2021-20021 removes that barrier without authentication, so a network-reachable management interface effectively becomes remote code execution with full loss of confidentiality, integrity and availability. CISA flags the vulnerability for known ransomware campaign use, and its exploitation likelihood ranks among the highest of all CVEs. Attackers use the mail gateway as a beachhead into the internal network and Active Directory. If your management UI is internet-facing or you still run 10.0.9.x, treat this as critical and assume possible compromise until hunting proves otherwise. If the interface is verifiably internal-only, high priority with patching within a few days is defensible.
Runbook step 1
Immediate response (0-24 h)
- Apply the vendor patch: Update every SonicWall Email Security instance (software 10.0.9.6103 and appliances 3300/4300/5000/5050/7000/7050/8300 on firmware 10.0.9.6105). A patch is available from the vendor — look up the fixed version in the vendor advisory. Close the chained CVE-2021-20021 and CVE-2021-20023 in the same maintenance window.
- Pull the admin UI off the internet: Immediately restrict the web management interface (HTTP/HTTPS, 80/443 by default) to a dedicated admin network or jump host. Mail flow on SMTP 25 can keep running.
- Audit administrator accounts: Reconcile all local admin accounts against your known baseline. CVE-2021-20021 allows unauthenticated admin account creation, which satisfies the "post-auth" precondition for this bug. Disable unknown accounts and preserve them for forensics rather than deleting them.
- Rotate credentials: Reset passwords for all admin accounts and stored service credentials (LDAP/AD bind, SMTP relay). If compromise is suspected, hunt for lateral movement using the AD service account.
- Hunt for web shells on the host: Look for new or modified .jsp, .jspx, .war or unexpected .zip files in the Tomcat-based backend's web application directories. Preserve any hits and isolate the host.
- Check reporting duties: If compromise is confirmed, prepare the NIS2 24-hour early warning to your national CSIRT or competent authority.
Runbook step 2
Mitigation layers
- Network segmentation: Place the appliance in a DMZ and allow only SMTP inbound from the internet. Permit management ports solely from the admin VLAN. Restrict the host's egress to required destinations (downstream MTA, update servers, LDAP), and log and deny everything else.
- WAF/reverse proxy: Block upload endpoints of the management UI, especially the branding/customisation archive upload abused in the known chain, for non-approved source IPs. Reject multipart uploads carrying .jsp/.war content or ZIP archives with
../path components. - Endpoint hardening (Windows-hosted deployments): Use an EDR rule or ASR/AppLocker policy to prevent the Tomcat/Java process from launching
cmd.exe,powershell.exe,whoami.exe,net.exeandcertutil.exe. Minimise the service account's write permissions on web application directories. - IAM/least privilege: Require named admin accounts with strong passwords. Make the LDAP bind account read-only and keep it out of privileged AD groups.
- Configuration control: Deploy file integrity monitoring on the web application and configuration directories, with alerts forwarded to the SIEM.
Runbook step 3
Detection rules
- Process ancestry (Sysmon EID 1 / EDR): Watch for
java.exeortomcat*.exespawning shells or recon tools. Sigma shape:ParentImage|endswith: ['\java.exe','\tomcat9.exe'] AND Image|endswith: ['\cmd.exe','\powershell.exe','\whoami.exe','\net.exe']. - File creation (Sysmon EID 11): Flag new
.jsp/.jspx/.warfiles under the Tomcatwebappsorworkdirectories. KQL:DeviceFileEvents | where FolderPath has "webapps" and FileName endswith ".jsp" and InitiatingProcessFileName =~ "java.exe". - Web access logs: Look for POST file uploads to the management UI from non-admin source IPs, followed by GETs to previously unseen .jsp paths. Also flag requests containing
../traversal patterns, which indicate CVE-2021-20023 in the same intrusion. - Account events: Alert on new admin accounts in the appliance audit log, and on Windows Event ID 4720/4732 on the host, when no change ticket covers them.
- Network telemetry (Zeek/Suricata): Watch for outbound connections from the Email Security host to unusual destinations, such as tunnelling tools, odd ports or newly seen external IPs. Also flag spikes in LDAP queries from the bind account, which suggest AD enumeration.
- Process ancestry (Sysmon EID 1 / EDR): Watch for
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
SonicWall Email Security version 10.0.9.x contains a vulnerability that allows a post-authenticated attacker to upload an arbitrary file to the remote host.
Source: CSA/SingCERT, cvelistv5, NVD (NIST), CISA KEV Catalog
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 | Email Security |
|
|
| sonicwall | email_security |
|
|
| sonicwall | email_security_virtual_appliance |
|
|
| sonicwall | hosted_email_security |
|
|
Vendors and products
- SonicWall SonicWall Email Security
- SonicWall Email Security Appliance 3300 Firmware
- SonicWall Email Security Appliance 4300 Firmware
- SonicWall Email Security Appliance 5000 Firmware
- SonicWall Email Security Appliance 5050 Firmware
- SonicWall Email Security Appliance 7000 Firmware
- SonicWall Email Security Appliance 7050 Firmware
- SonicWall Email Security Appliance 8300 Firmware
- SonicWall Email Security Appliance 9000 Firmware
- SonicWall SonicWall Email Security Virtual Appliance
- SonicWall SonicWall Email Security
Affected operating systems
| Other | sonicwall | email_security_appliance_3300_firmware | — |
| Other | sonicwall | email_security_appliance_4300_firmware | — |
| Other | sonicwall | email_security_appliance_5000_firmware | — |
| Other | sonicwall | email_security_appliance_5050_firmware | — |
| Other | sonicwall | email_security_appliance_7000_firmware | — |
| Other | sonicwall | email_security_appliance_7050_firmware | — |
| Other | sonicwall | email_security_appliance_8300_firmware | — |
| Other | sonicwall | email_security_appliance_9000_firmware | — |
Weakness classes (CWE)
CWE-434Unrestricted Upload of File with Dangerous Type
Base
The product allows the upload or transfer of dangerous file types that are automatically processed within its environment.
Entry at MITRE CWE-434
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 | |
| CSA/SingCERT | Zero-Day Vulnerabilities in SonicWall Email Security (opens in a new tab)CSA/SingCERT | actively exploited |
References & sources
- psirt.global.sonicwall.comvuln-detail/SNWLID-2021-0008x_refsource_CONFIRM
- cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2021-20022government-resource
Changes to this CVE
Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).
Record modifiedsonicwall.com
Show 3 original changes
Individual changes of this event as published by NVD Type Action Before After Reference added —https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0008Reference removed https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0008—Reference type removed https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0008 Types: Vendor Advisory—Source identifier: PSIRT@sonicwall.com
Record modifiedCISA ADP
CISA assessment (SSVC): exploitation: active, automatable: yes
Show 5 original changes
Individual changes of this event as published by NVD Type Action Before After Reference added —https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-20022Reference removed https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-20022—Reference type removed https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-20022 Types: US Government Resource—SSVC assessment removed {"id":"CVE-2021-20022","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"yes"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2021-04-20T00:00:00+00:00"}—SSVC assessment added —{"id":"CVE-2021-20022","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"yes"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-08-12T03:55:23.619977Z"}Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0
Record modifiedCVE Program
Show 3 original changes
Individual changes of this event as published by NVD Type Action Before After Reference added —https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0008Reference removed https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0008—Reference type removed https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0008 Types: Vendor Advisory—Source identifier: af854a3a-2127-422b-91ae-364da2661108
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<a href="https://intel.neosec.eu/en/cve/CVE-2021-20022"><img src="https://intel.neosec.eu/badge/cve/CVE-2021-20022.svg?lang=en" alt="CVE-2021-20022 – NEOSEC Intel" height="20"></a>