The Wordfence Threat Intelligence team has been tracking a large-scale attack against a Remote Code Execution vulnerability in Tatsu Builder, which is tracked by CVE-2021-25094 and was publicly disclosed on March 24, 2022, by an independent security researcher. The issue is present in vulnerable versions of both the free and premium Tatsu Builder plugin.

The following is a graph showing the total volume of attacks targeting the vulnerability in Tatsu Builder.

Graph showing attack volume against CVE-2021-25094

Indicators of Attack

Most of the attacks we have seen are probing attacks to determine the presence of a vulnerable plugin. These may appear in your logs with the following query string:

/wp-admin/admin-ajax.php?action=add_custom_font

The vast majority of attacks are the work of just a few IP addresses.

The top 3 attacking IPs have each attacked over 1 million sites:

148.251.183.254
176.9.117.218
217.160.145.62

An additional 15 IPs have each attacked over 100,000 sites:

65.108.104.19
62.197.136.102
51.38.41.15
31.210.20.170
31.210.20.101
85.202.169.175
85.202.169.71
85.202.169.86
85.202.169.36
85.202.169.83
85.202.169.92
194.233.87.7
2.56.56.203
85.202.169.129
135.181.0.188

Indicators of Compromise

The most common payload we’ve seen is a dropper used to place additional malware located in a randomly-named subfolder of wp-content/uploads/typehub/custom/ such as wp-content/uploads/typehub/custom/vjxfvzcd.

The dropper is typically named .sp3ctra_XO.php and has an MD5 hash of 3708363c5b7bf582f8477b1c82c8cbf8.

Note the dot at the beginning as this indicates a hidden file, which is necessary to exploit the vulnerability as it takes advantage of a race condition.

This file is detected by the Wordfence scanner.

If you use the Tatsu Builder plugin, we strongly recommend updating to the latest version available, which is 3.3.13 at the time of this writing. Please note that version 3.3.12 contained a partial patch but did not fully address all issues.

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