CVE-2021-20729Network attack vector

Reflected XSS via unencoded captive-portal redirect URL

Published Mar 31, 2022 · Updated Aug 3, 2024

Cross-site scripting in pfSense CE 2.5.2 and earlier and pfSense Plus 21.05 and earlier allows remote attackers to run script via a malicious URL. The Captive Portal client login page neither validates the redirurl field nor encodes its value before inserting it into the resulting link. Exploitation requires a logged-in captive portal user to visit the crafted login URL and follow that link, exposing browser-session data without affecting the firewall itself.

CVSS severity6.1
Medium
EPSS probability2.88%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in pfSense CE 2.5.2 and earlier and pfSense Plus 21.05 and earlier allows remote attackers to run script via a malicious URL. The Captive Portal client login page neither validates the redirurl field nor encodes its value before inserting it into the resulting link. Exploitation requires a logged-in captive portal user to visit the crafted login URL and follow that link, exposing browser-session data without affecting the firewall itself.

The record

CVE
CVE-2021-20729
Published
Mar 31, 2022
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-79, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 31, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
6.1JPCERT/CC and IPACVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
4.3JPCERT/CC and IPAAV:N/AC:M/Au:N/C:N/I:P/A:N
6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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