At a glance

CVE-2023-26326 is a high-severity Deserialization of Untrusted Data vulnerability in the Post Form WordPress plugin, affecting versions <= 2.7.7. It carries a CVSS score of 8.8 (reachable over the network; low attack complexity; high confidentiality, integrity, availability impact). The issue is fixed in version 2.7.8; sites on affected versions should update now. Disclosed February 2023, reported by Joshua Martinelle.

Vulnerability Overview

The BuddyForms plugin for WordPress is vulnerable to deserialization of untrusted input via the 'url' parameter in versions up to, and including 2.7.7. This makes it possible for authenticated attackers with minimal permissions, such as a subscriber, to call files using a PHAR wrapper that will deserialize the data and call arbitrary PHP Objects that can be used to perform a variety of malicious actions granted a POP chain is also present. It also requires that the attacker is successful in uploading a file with the serialized payload, however, this can easily be achieved by uploading a fake profile photo prior to launching an attack.

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. A successful exploit has high impact on confidentiality, integrity, availability — full site compromise territory.

CWE-502: Deserialization of Untrusted Data

Post Form <= 2.7.7 carries this weakness at url, and reaching it takes a caller who can reach the endpoint. Deserialization of untrusted data means the application reconstructs objects from input a caller controls, letting the attacker choose which classes get instantiated and what their properties hold.

A workable chain turns deserialization into file writes, deletions or code execution, depending on what the loaded classes do in their magic methods. For Post Form the fix is 2.7.8: builds <= 2.7.7 are affected, anything from 2.7.8 onward is not.

Remediation

Update to version 2.7.8, or a newer patched version

How does WordSec protect against this?

The attempt arrives as an ordinary request to Post Form: WordSec's web application firewall inspects request payloads before WordPress loads them. Classes like this one can leave something behind, so the staged malware scanner is the second half: it looks for dropped files and modified code rather than for the request that created them. None of that substitutes for the fix: Post Form 2.7.8 closes this, and updating the plugin is the step that ends it.

  • Firewall
  • Scanner
  • Alerts

External References

Related records

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