CVE-2018-20148

WordPress Core < 5.0.1 - PHP Object Injection

2018-12-12 00:00
Sam Thomas

Strategic Overview

Status
Patched in 3.7.28
Affected Core
WordPress 5.0
Affected Version
3.7 – 5.0 · 15 branches
CVSS
8.8High
Weakness type
CWE-502 · Deserialization of Untrusted Data
CVE
CVE-2018-20148
View all WordPress 5.0 vulnerabilities

At a glance

CVE-2018-20148 is a high-severity Deserialization of Untrusted Data vulnerability in the WordPress 5.0 WordPress release line, affecting 3.7 – 5.0 · 15 branches. 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 3.7.28; sites on affected versions should update now. Disclosed December 2018, reported by Sam Thomas.

Vulnerability Overview

In WordPress before 4.9.9 and 5.x before 5.0.1, contributors could conduct PHP object injection attacks via crafted metadata in a wp.getMediaItem XMLRPC call. This is caused by mishandling of serialized data at phar:// URLs in the wp_get_attachment_thumb_file function in wp-includes/post.php.

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

Reaching this weakness in WordPress 5.0 3.7 – 5.0 · 15 branches 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 WordPress 5.0 the fix is 3.7.28: builds 3.7 – 5.0 · 15 branches are affected, anything from 3.7.28 onward is not.

Remediation

Update to one of the following versions, or a newer patched version: 3.7.28, 3.8.28, 3.9.26, 4.0.25, 4.1.25, 4.2.22, 4.3.18, 4.4.17, 4.5.16, 4.6.13, 4.7.12, 4.8.8, 4.9.9, 5.0.1

How does WordSec protect against this?

The attempt arrives as an ordinary request to WordPress 5.0: 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: updating to 3.7.28 is the step that ends it.

  • Firewall
  • Scanner
  • Alerts

External References

https://www.cve.org/CVERecord?id=CVE-2018-20148https://www.wordfence.com/threat-intel/vulnerabilities/id/29778d95-4859-4383-91c7-15e7907b825chttps://nvd.nist.gov/vuln/detail/CVE-2018-20148

Related records

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