CVE-2021-20023: SonicWall Email Security Path Traversal Vulnerability

Q: How do I fix CVE-2021-20023?

email security: upgrade to 10.0.9.6173; email security appliance 9000 firmware: upgrade to 10.0.9.6177; email security appliance 3300 firmware: upgrade to 10.0.9.6177. Exact commands for each OS are on this page.

Q: Is CVE-2021-20023 being exploited?

Yes. CVE-2021-20023 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

Q: What does CVE-2021-20023 affect?

CVE-2021-20023 affects email security, email security appliance 9000 firmware, email security appliance 3300 firmware. Severity is medium (CVSS 4.9). 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.

Q: How urgent is CVE-2021-20023?

Priority 72/100. EPSS top 1%: very likely to be exploited; Exploited in the wild (CISA KEV); Used in ransomware campaigns

Patch now

MEDIUM 4.9EXPLOITEDUPGRADEUPGRADEUPGRADE

CVE-2021-20023 is a medium-severity flaw (CVSS 4.9) affecting email security, email security appliance 9000 firmware, email security appliance 3300 firmware, reported as exploited in the wild. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

EPSS top 1%: very likely to be exploited
Exploited in the wild (CISA KEV)
Used in ransomware campaigns

A fixed release or distro patch exists.

Risk facts

CVSS score	4.9 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	High
User interaction	None
EPSS exploit chance	51.7% (top 1%)
CISA exploited list	Yes, fix due 2021-11-17, used in ransomware
Weakness	CWE-22
Published	2021-04-20
Last modified	2026-10-01

Publisher (CNA): SonicWALL, Inc. · Vendor: sonicwall

Last updated 2026-10-01 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-04-20 12:15 UTCPublished CVE record published
2021-11-03Exploited Added to the CISA Known Exploited Vulnerabilities list
2021-11-17Deadline CISA due date for US federal agencies to patch
2026-10-01 21:17 UTCUpdated Record last modified

sonicwall email security UPGRADE

Affected: < 10.0.9.6173

Fixed in: 10.0.9.6173

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy email-security || rpm -q email-security || email-security --version

2. UPGRADE to 10.0.9.6173 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade email-security

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade email-security

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

sonicwall email security appliance 9000 firmware UPGRADE

Affected: < 10.0.9.6177

Fixed in: 10.0.9.6177

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

sonicwall email security appliance 3300 firmware UPGRADE

Affected: < 10.0.9.6177

Fixed in: 10.0.9.6177

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

sonicwall email security appliance 4300 firmware UPGRADE

Affected: < 10.0.9.6177

Fixed in: 10.0.9.6177

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

sonicwall email security appliance 8300 firmware UPGRADE

Affected: < 10.0.9.6177

Fixed in: 10.0.9.6177

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

sonicwall email security appliance 5000 firmware UPGRADE

Affected: < 10.0.9.6177

Fixed in: 10.0.9.6177

Safe to downgrade to: no unaffected older release

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · CISA KEV catalog · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-20023?

email security: upgrade to 10.0.9.6173; email security appliance 9000 firmware: upgrade to 10.0.9.6177; email security appliance 3300 firmware: upgrade to 10.0.9.6177. Exact commands for each OS are on this page.

Is CVE-2021-20023 being exploited?

Yes. CVE-2021-20023 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

What does CVE-2021-20023 affect?

CVE-2021-20023 affects email security, email security appliance 9000 firmware, email security appliance 3300 firmware. Severity is medium (CVSS 4.9). 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.

How urgent is CVE-2021-20023?

Priority 72/100. EPSS top 1%: very likely to be exploited; Exploited in the wild (CISA KEV); Used in ransomware campaigns

Software pages

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References

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