CVE-2017-20207

The Flickr Gallery plugin for WordPress is vulnerable to PHP Object Injection in versions up to, and including, 1.5.2 via deserialization of untrusted input from the pager parameter. This allows unauthenticated attackers to inject a PHP Object. Attackers were actively exploiting this vulnerability with the WP_Theme() class to create backdoors.

Weakness

The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.

Potential Mitigations

• Make fields transient to protect them from deserialization.
• An attempt to serialize and then deserialize a class containing transient fields will result in NULLs where the transient data should be. This is an excellent way to prevent time, environment-based, or sensitive variables from being carried over and used improperly.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/586.html

References

• https://plugins.trac.wordpress.org/changeset/1737576/flickr-gallery
• https://www.wordfence.com/blog/2017/10/3-zero-day-plugin-vulnerabilities-exploited-wild/
• https://www.wordfence.com/threat-intel/vulnerabilities/id/b52ae51d-7b9a-4047-82bf-723ea87d2375?source=cve