CVE-2021-4422

POST SMTP Mailer <= 2.0.20 - Cross-Site Request Forgery Bypass

2021-03-01 00:00
Jerome Bruandet

Strategic Overview

Status
Patched in 2.0.21
Affected Plugin
Post SMTP – Complete Email Deliverability and SMTP Solution with Email Logs, Alerts, Backup SMTP & Mobile App
Affected Version
<= 2.0.20
CVSS
4.3Medium
Weakness type
CWE-352 · Cross-Site Request Forgery (CSRF)
CVE
CVE-2021-4422
View all Post SMTP – Complete Email Deliverability and SMTP Solution with Email Logs, Alerts, Backup SMTP & Mobile App vulnerabilities

At a glance

CVE-2021-4422 is a medium-severity Cross-Site Request Forgery (CSRF) vulnerability in the Post SMTP WordPress plugin, affecting versions <= 2.0.20. It carries a CVSS score of 4.3 (reachable over the network; low attack complexity). Exploitation requires no authentication. The issue is fixed in version 2.0.21; sites on affected versions should update now. Disclosed March 2021, reported by Jerome Bruandet.

Vulnerability Overview

The POST SMTP Mailer plugin for WordPress is vulnerable to Cross-Site Request Forgery in versions up to, and including, 2.0.20. This is due to missing or incorrect nonce validation on the handleCsvExport() function. This makes it possible for unauthenticated attackers to trigger a CSV export via a forged request granted they can trick a site administrator into performing an action such as clicking on a link.

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 privileges on the target site.

CWE-352: Cross-Site Request Forgery (CSRF)

Post SMTP <= 2.0.20 carries this weakness at handleCsvExport(), and reaching it takes a caller who can reach the endpoint. Cross-site request forgery abuses the fact that browsers attach a victim's cookies to any request, so a state-changing action that only checks who you are, not whether you meant to act, can be triggered from another site.

An attacker who gets a logged-in user to load a crafted page can perform that action as them, with the impact scaling to whatever the victim's role is allowed to do. For Post SMTP the fix is 2.0.21: builds <= 2.0.20 are affected, anything from 2.0.21 onward is not.

Remediation

Update to version 2.0.21, or a newer patched version

How does WordSec protect against this?

The attempt arrives as an ordinary request to Post SMTP: WordSec's web application firewall inspects request payloads before WordPress loads them. None of that substitutes for the fix: Post SMTP 2.0.21 closes this, and updating the plugin is the step that ends it.

  • Firewall
  • Alerts

External References

https://www.cve.org/CVERecord?id=CVE-2021-4422https://www.wordfence.com/threat-intel/vulnerabilities/id/e018ca7c-06dd-4d40-91d4-4ed188b8aaf2https://nvd.nist.gov/vuln/detail/CVE-2021-4422

Related records

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