CVE-2021-20137Public exploitNetwork attack vector

Browser script execution via reflected URL parameter

Published Dec 9, 2021 · Updated Aug 3, 2024

Reflected XSS in Gryphon Tower 04.0004.12 and earlier allows remote attackers to execute JavaScript through a crafted site-access URL. The /cgi-bin/luci/site_access/ handler places the url query value into an HTML attribute without neutralizing attacker-controlled event-handler syntax. The script runs only after a victim follows the link and is limited to the web origin and privileges available to that browser session.

CVSS severity4.3
Medium
EPSS probability2.56%
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 Gryphon Tower 04.0004.12 and earlier allows remote attackers to execute JavaScript through a crafted site-access URL. The /cgi-bin/luci/site_access/ handler places the url query value into an HTML attribute without neutralizing attacker-controlled event-handler syntax. The script runs only after a victim follows the link and is limited to the web origin and privileges available to that browser session.

The record

CVE
CVE-2021-20137
Published
Dec 9, 2021
Updated
Aug 3, 2024
Vendor
Gryphon Online Safety, Inc.
Product
Gryphon Tower
Classifications
CWE-79, T1204.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 9, 2021CVE 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

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=<= 04.0004.12 (Current)

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Gryphon Online Safety, Inc. · Gryphon Towerversion=<= 04.0004.12 (Current)

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
4.3TenableCVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:N/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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1204.001Malicious Link

Public exploit references

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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