CVE-2020-21054Network attack vector

Reflected XSS via unsanitized f parameter

Published May 20, 2021 · Updated Aug 4, 2024

Reflected XSS in FusionPBX 4.5.7 allows remote attackers to execute arbitrary script in a user's browser through a crafted URL. The app/vars/vars_textarea.php page places the unsanitized f parameter into generated HTML, allowing browser interpretation as script or markup. Exploitation requires a user to follow the crafted URL; successful script runs in the FusionPBX origin and can read or modify data available to that user's session.

CVSS severity6.1
Medium
EPSS probability0.72%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reflected XSS in FusionPBX 4.5.7 allows remote attackers to execute arbitrary script in a user's browser through a crafted URL. The app/vars/vars_textarea.php page places the unsanitized f parameter into generated HTML, allowing browser interpretation as script or markup. Exploitation requires a user to follow the crafted URL; successful script runs in the FusionPBX origin and can read or modify data available to that user's session.

The record

CVE
CVE-2020-21054
Published
May 20, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-79, T1204.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 20, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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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

6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/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')
T1204.001User Execution: Malicious Link

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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