Leaky Paywall <= 4.16.5 Authenticated Stored Cross-Site Scripting
Strategic Overview
- Status
- Patched in 4.16.6
- Affected Plugin
- Leaky Paywall
- Affected Version
<= 4.16.5- CVSS
- 5.5Medium
- Weakness type
- CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
- CVE
CVE-2021-39357
At a glance
CVE-2021-39357 is a medium-severity Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in the Leaky Paywall WordPress plugin, affecting versions <= 4.16.5. It carries a CVSS score of 5.5 (reachable over the network; low attack complexity). Exploitation requires an authenticated account. The issue is fixed in version 4.16.6; sites on affected versions should update now. Disclosed October 2021, reported by Thinkland Security Team.
Vulnerability Overview
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.
Technical Analysis
The vector marks this flaw as remotely reachable over the network, with low attack complexity — no special timing or configuration is needed, and no interaction from a victim user.
CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Reaching this weakness in Leaky Paywall <= 4.16.5 takes any authenticated account. Cross-site scripting happens when input from a request is written into a page without being escaped for the context it lands in, so the browser parses attacker-supplied text as markup or script.
Injected script runs with the privileges of whoever views the affected page, which is how these flaws turn into administrator session theft, silent account creation or persistent backdoors in page content. For Leaky Paywall the fix is 4.16.6: builds <= 4.16.5 are affected, anything from 4.16.6 onward is not.
Remediation
Update to version 4.16.6, or a newer patched version
How does WordSec protect against this?
The attempt arrives as an ordinary request to Leaky Paywall: WordSec's web application firewall inspects request payloads before WordPress loads them. None of that substitutes for the fix: Leaky Paywall 4.16.6 closes this, and updating the plugin is the step that ends it.
- Firewall
- Alerts
External References
Related records
Same weakness class
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