CVE-2021-39357Public exploitNetwork attack vector

Administrator stored XSS via unsanitized class.php input

Published Oct 21, 2021 · Updated Feb 14, 2025

Stored XSS in ZEEN101 Leaky Paywall 4.16.5 and earlier allows remote authenticated users to inject scripts through class.php. The published record identifies insufficient input validation and sanitization in class.php but does not disclose the affected function or input field. Exploitation requires administrator access and a configuration that removes unfiltered_html; injected scripts execute in a later viewer's browser.

CVSS severity5.5
Medium
EPSS probability0.92%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Stored XSS in ZEEN101 Leaky Paywall 4.16.5 and earlier allows remote authenticated users to inject scripts through class.php. The published record identifies insufficient input validation and sanitization in class.php but does not disclose the affected function or input field. Exploitation requires administrator access and a configuration that removes unfiltered_html; injected scripts execute in a later viewer's browser.

The record

CVE
CVE-2021-39357
Published
Oct 21, 2021
Updated
Feb 14, 2025
Vendor
ZEEN101
Product
Leaky Paywall
Classifications
CWE-79, T1059.007
Attack vector
network
Privileges
admin

Timeline

How it unfolded

  1. Oct 21, 2021CVE publishedPublication date reported by the CVE source.
  2. Feb 14, 2025Record 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=4.16.5 <=4.16.5

What conditions does exploitation require?

Attack vectornetwork
Required privilegesadmin

What is affected?

ZEEN101 · Leaky Paywallversion=4.16.5 <=4.16.5

Published CVSS scores

5.5WordfenceCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:L/I:L/A:N
3.5NIST NVDAV:N/AC:M/Au:S/C:N/I:P/A:N
4.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:H/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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesadmin
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1059.007Command and Scripting Interpreter: JavaScript/JScript

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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