CVE-2021-20021
CriticalExploitedPublic exploitA vulnerability in the SonicWall Email Security version 10.0.9.x allows an attacker to create an administrative account by sending a crafted HTTP request to the remote host.
Published Apr 21, 2021 · Updated Aug 12, 2026 · Also known as TR-21-0337
Key Facts
Patch immediately- CVE-2021-20021 is a critical-severity vulnerability (CVSS 9.8 v3.1) affecting Email Security (Sonicwall), Email Security Virtual Appliance (Sonicwall), Hosted Email Security (Sonicwall) and 8 more products.
- It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Apr 20, 2021 and is known to be used in ransomware campaigns. Public exploit code is available.
- EPSS estimates a 89% probability of exploitation in the next 30 days.
- Fixed versions are available, including Email Security 10.0.9.6103, Email Security Appliance 3300 Firmware 10.0.9.6105, Email Security Appliance 4300 Firmware 10.0.9.6105.
- Brandefense priority: patch immediately, because it is listed as exploited in the wild.
CVSS v3.1
9.8
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS (30-day exploit likelihood)
89%
Higher than 99.7% of all scored CVEs
Exploited in the wild
Yes
4 catalog listings, used by ransomware
Public exploit code
Available
Proof-of-concept or weaponized module
Get the full CVE-2021-20021 brief as a PDF
Every affected product and fixed release, exploitation status and a first 24 hours response checklist, emailed within minutes.
Description
A vulnerability in the SonicWall Email Security version 10.0.9.x allows an attacker to create an administrative account by sending a crafted HTTP request to the remote host.
Known-Exploited Catalog Listings
| Catalog | Added | Remediation due | Ransomware use |
|---|---|---|---|
| CISA KEV | Nov 3, 2021 | Nov 17, 2021 | Known |
| Industry KEV feed | Apr 20, 2021 | Nov 17, 2021 | Known |
| CIRCL KEV | Nov 3, 2021 | Nov 17, 2021 | Known |
| ENISA EUVD | Nov 3, 2021 | n/a | Not reported |
Required action: Apply updates per vendor instructions.
Affected Products
12 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| Email SecuritySonicwall | >= 10.0.9 and earlier | 10.0.9.6103 |
| Email Security Virtual ApplianceSonicwall | See advisory | 10.0.9.6105 |
| Hosted Email SecuritySonicwall | See advisory | 10.0.9.6103 |
| Email Security Appliance 3300 FirmwareSonicwall | See advisory | 10.0.9.6105 |
| Email Security Appliance 4300 FirmwareSonicwall | See advisory | 10.0.9.6105 |
Patched Releases
Email Security
10.0.9.6103
Email Security Appliance 3300 Firmware
10.0.9.6105
Email Security Appliance 4300 Firmware
10.0.9.6105
Email Security Appliance 5000 Firmware
10.0.9.6105
Email Security Appliance 5050 Firmware
10.0.9.6105
Email Security Appliance 7000 Firmware
10.0.9.6105
Email Security Appliance 7050 Firmware
10.0.9.6105
Email Security Appliance 8300 Firmware
10.0.9.6105
Email Security Appliance 9000 Firmware
10.0.9.6105
Email Security Virtual Appliance
10.0.9.6105
Hosted Email Security
10.0.9.6103
Timeline
Added to Industry KEV feed
Apr 20, 2021
Publicly disclosed
Apr 21, 2021
Added to CISA KEV
Nov 3, 2021
Added to CIRCL KEV
Nov 3, 2021
Added to ENISA EUVD
Nov 3, 2021
Last updated
Aug 12, 2026
Weakness Type
- CWE-269 Improper Privilege Management
References
- advisoryhttps://kkhacklabs.com/3-zero-day-exploits-hit-sonicwall-enterprise-email-security-appliances/
- advisoryhttps://psirt.global.sonicwall.com/vuln-detail/SNWLID-2021-0007
- advisoryhttps://us-cert.cisa.gov/ics/advisories/icsa-21-110-07
- advisoryhttps://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-20023
- advisoryVulnCheck exploitation report
FAQ
Common Questions.
A vulnerability in the SonicWall Email Security version 10.0.9.x allows an attacker to create an administrative account by sending a crafted HTTP request to the remote host.
Affected: Email Security (Sonicwall) versions >= 10.0.9 and earlier; Email Security Virtual Appliance (Sonicwall); Hosted Email Security (Sonicwall), among others. The full list is in the CVE brief.
It is exploited in the wild, listed in CISA KEV, Industry KEV feed, CIRCL KEV, ENISA EUVD since Apr 20, 2021 and is known to be used in ransomware campaigns.
Yes. It was added on Nov 3, 2021 with a federal remediation due date of Nov 17, 2021.
Public exploit code is available.
Fixed versions are available, including Email Security 10.0.9.6103, Email Security Appliance 3300 Firmware 10.0.9.6105, Email Security Appliance 4300 Firmware 10.0.9.6105.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.
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