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PfsenseApplication

CVE-2021-20729

MEDIUM · 6.1 CVSS v3.1 Published 2022-03-31
Fix available
A fix is available. Upgrade to after 21.05 or later.
See remediation →
68/100
Remediation priority · Elevated
Remotely reachable No privileges

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Cross-site scripting vulnerability in pfSense CE and pfSense Plus (pfSense CE software versions 2.5.2 and earlier, and pfSense Plus software versions 21.05 and earlier) allows a remote attacker to inject an arbitrary script via a malicious URL.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Reflected cross-site scripting (XSS) vulnerability in pfSense CE and pfSense Plus web interface. An attacker can craft a malicious URL containing arbitrary JavaScript that executes in the victim's browser when clicked, due to improper input validation and output encoding in the affected pfSense versions.

MitigationUpgrade pfSense CE to version 2.5.3 or later, and pfSense Plus to version 21.05.1 or later. As interim controls, deploy a WAF/URL filtering and warn users against clicking untrusted links.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
PfsenseApplication
Affected:<= 2.5.2
Pfsense PlusApplication
Affected:<= 21.05

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify the pfSense product variant
    Log into the pfSense web interface and check the dashboard, or run `pfSense-version` via SSH/shell to determine if you are running pfSense CE or pfSense Plus
    Affected if The product variant is unclear or unknown, making version comparison impossible
  2. Determine the installed pfSense CE version
    In the web UI, go to System > Firmware > Version, or via command line run `pfSense-version` or check `cat /etc/version`
    Affected if The installed version is 2.5.2 or earlier (CE branch)
  3. Determine the installed pfSense Plus version
    In the web UI, go to System > Firmware > Version, or via command line run `pfSense-version` or check `cat /etc/version`
    Affected if The installed version is 21.05 or earlier (Plus branch)
  4. Confirm web interface accessibility
    Verify that the pfSense web interface (nginx/lighttpd on port 443/80) is enabled and reachable. Check via `ps aux | grep -E 'nginx|lighttpd'` or by attempting to access the UI URL
    Affected if The web interface is enabled and accessible - this is required for the XSS to be exploitable

You are affected if the pfSense web interface is enabled AND your installed version is pfSense CE <= 2.5.2 or pfSense Plus <= 21.05.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to a release after 21.05
Interim mitigation

Upgrade pfSense CE to version 2.5.3 or later, and pfSense Plus to version 21.05.1 or later. As interim controls, deploy a WAF/URL filtering and warn users against clicking untrusted links.

Recommended fix Moderate confidence

pfSense CE 2.5.3 or later / pfSense Plus 21.09 or later

  1. 1. Back up the current pfSense configuration via System > Backup & Restore > Backup configuration
  2. 2. Download the configuration backup to a secure location
  3. 3. Access the pfSense web interface and navigate to System > Update > System Update
  4. 4. If using pfSense CE, select a version higher than 2.5.2 (such as 2.5.3 or 2.6.0)
  5. 5. If using pfSense Plus, select a version higher than 21.05 (such as 21.09 or later)
  6. 6. Apply the upgrade and allow the system to reboot
  7. 7. After reboot, verify the upgrade was successful and restore the configuration if needed
Caveat Minor: Review release notes for any configuration changes between versions; some packages may need reinstallation

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Pfsense Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing2.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,600
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Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-20729 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data