SonicWall Email Security Path Traversal Vulnerability (CVE-2021-20023)
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 read an arbitrary file on 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 10.0.9.6173, email_security_virtual_appliance to version 10.0.9.6177, hosted_email_security to version 10.0.9.6173. 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
4.9
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: NVD, CVSS v3
4.9
CVSS v3
Severity Medium on the scale from 0 to 10.
Source: SingCERT, CVE.org
51.7 %
EPSS score
High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
Source: FIRST EPSS, percentile 99.0
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- 227.83 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- 4.9 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- 4.9
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- 51.7 %
- High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
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- 99.0
- 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-22
Response and mitigation
Why act now?
Prioritisation rationale
On its own this looks like a moderate bug because it requires high-privilege authentication. In practice, CVE-2021-20021 removes that barrier entirely, and the full chain of account creation, file read and file upload delivers complete system takeover. CISA explicitly flags its use in ransomware campaigns, and exploitation likelihood is very high. Typical targets are organisations exposing the Email Security admin UI to the internet, with the appliance then used as a foothold into Active Directory via stored LDAP credentials. If your admin UI is internet-facing, treat this as top priority and include a compromise assessment. If it is reachable only internally, patch promptly in the next emergency change window.
Runbook step 1
Immediate response (0-24 h)
- Scope exposure: Inventory every SonicWall Email Security instance (hardware appliances 3300/4300/5000/5050/7000/7050/8300, virtual appliances and Windows software installs) and confirm the version. The affected branch is 10.0.9.x (including 10.0.9.6173 and firmware 10.0.9.6177).
- Patch: A patch is available from the vendor — look up the fixed version in the SonicWall PSIRT advisory, which covers CVE-2021-20021/-20022/-20023 together. Because the three bugs are chained, fix all three in the same window. Patching only this CVE leaves the chain usable.
- Pull the admin UI off the internet: Restrict the web management interface (HTTP/HTTPS admin UI) to a dedicated management network or VPN immediately. Mail flow over SMTP is unaffected.
- Rule out compromise: Review the administrator account list in the Email Security console for unknown or recently created accounts. CVE-2021-20021 allows unauthenticated admin creation, which supplies the "authentication" this CVE requires. Disable suspicious accounts and preserve evidence before deleting them.
- Rotate secrets: Arbitrary file read exposes configuration and credential files. Rotate admin passwords, LDAP/AD bind accounts, SMTP relay credentials and any API keys stored on the appliance.
- Preserve evidence: If compromise is suspected, snapshot or image the appliance or Windows host before patching. Collect Tomcat logs, audit logs and the webapps directory.
Runbook step 2
Mitigation layers
- Network segmentation: Allow admin UI access only from a management VLAN (ACL: source = admin jump hosts, destination = appliance management port). Restrict appliance egress to SMTP, update servers and other defined destinations to block reverse shells and exfiltration.
- WAF/IPS: Place a reverse proxy or WAF in front of the management UI that blocks traversal patterns (
../,..%2f,%2e%2e%2f,..\,%5c). Enable SonicWall Email Security / CVE-2021-20023 signatures in Suricata/Snort or the NGFW in blocking mode. - IAM/least privilege: Minimise the number of admin accounts and enforce MFA on console access where supported. Give LDAP bind accounts read-only rights.
- Endpoint hardening (Windows installs): Run EDR on the host. Use ASR or AppLocker rules to block, or at least alert on, the Tomcat/Java process spawning
cmd.exe,powershell.exeorwhoami.exe. Put the webapps directory under file integrity monitoring. - Configuration: Disable admin UI features you don't use operationally, such as branding/upload functions. Review lifecycle plans for end-of-life hardware.
Runbook step 3
Detection rules
- Web/Tomcat access logs: Look for traversal sequences in requests to the admin UI. Example SPL:
index=proxy dest=<ES-appliance> (uri="*../*" OR uri="*%2e%2e*" OR uri="*..%2f*" OR uri="*..%5c*"). Prioritise HTTP 200 responses with unusually large response sizes. - Process ancestry (Sysmon EID 1 / EDR): Java/Tomcat spawning shells. Sigma shape:
ParentImage|endswith: '\java.exe'ANDImage|endswith: ['\cmd.exe','\powershell.exe','\whoami.exe','\net.exe']. - Webshell drop (Sysmon EID 11): New
.jsp,.jspxor.warfiles under the Email Security Tomcat webapps directory that don't originate from a vendor update. - Application audit log: New admin accounts, role changes, or logins from unfamiliar source IPs. A login shortly after an account is created is a strong signal of the 20021→20023→20022 chain.
- Network telemetry (Zeek/Suricata): New outbound non-SMTP connections or unusually high outbound volume from the appliance. Also watch for LDAP bind account logons from hosts other than the appliance (Windows Event ID 4624/4625 on DCs).
- Web/Tomcat access logs: Look for traversal sequences in requests to the admin UI. Example SPL:
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 read an arbitrary file on 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-22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Base
The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.
Entry at MITRE CWE-22
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-2021-0010x_refsource_CONFIRM
- cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2021-20023government-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 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-2021-0010Reference removed https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0010—Reference type removed https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0010 Types: Vendor Advisory—Source identifier: af854a3a-2127-422b-91ae-364da2661108
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-2021-0010Reference removed https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0010—Reference type removed https://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0010 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-2021-20023Reference removed https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-20023—Reference type removed https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-20023 Types: US Government Resource—SSVC assessment removed {"id":"CVE-2021-20023","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-2021-20023","role":"CISA Coordinator","options":[{"exploitation":"active"},{"automatable":"yes"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-08-12T03:55:24.717669Z"}Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0
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<a href="https://intel.neosec.eu/en/cve/CVE-2021-20023"><img src="https://intel.neosec.eu/badge/cve/CVE-2021-20023.svg?lang=en" alt="CVE-2021-20023 – NEOSEC Intel" height="20"></a>