Millions of Attacks Target Tatsu Builder Plugin

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. Tatsu Builder is a proprietary plugin that is not listed on the repository, so reliable installation counts are not available, but we estimate that the plugin has between 20,000 and 50,000 installations. Tatsu sent an urgent email notification to all of their customers on April 7th advising them to update, but we estimate that at least a quarter of remaining installations are still vulnerable.

All Wordfence users with the Wordfence Web Application Firewall active, including Wordfence free customers, are protected against attackers trying to exploit this vulnerability.

We began seeing attacks on May 10, 2022. The attacks are ongoing with the volume ramping up to a peak of 5.9 million attacks against 1.4 million sites on May 14, 2022. The attack volume has declined but the attacks are still ongoing at the time of publication.

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

While the following is a graph showing the total number of sites being targeted by attackers trying to exploit the vulnerability in Tatsu Builder.

Description: Unauthenticated Remote Code Execution
Affected Plugin: Tatsu Builder
Plugin Slug: tatsu
Plugin Developer: BrandExponents
Affected Versions: < 3.3.13
CVE ID: CVE-2021-25094
CVSS Score: 8.1 (High)
Researcher/s: Vincent Michel (darkpills)
Fully Patched Version: 3.3.13

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:


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:

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

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.

What Should I Do?

All Wordfence users with the Wordfence Web Application Firewall active, including Wordfence free customers, are protected against this vulnerability. Nonetheless, 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.

If you know anyone using the Tatsu Builder plugin on their site, we urge you to forward this article to them as this is a large-scale attack and any vulnerable sites that are not updated and not using some form of a Web Application Firewall are at risk of complete site takeover.

If you believe your site has been compromised as a result of this vulnerability or any other vulnerability, we offer Incident Response services via Wordfence Care. If you need your site cleaned immediately, Wordfence Response offers the same service with 24/7/365 availability and a 1-hour response time. Both these products include hands-on support in case you need further assistance.

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  • Thanks, WordFence for this advisory. Although I'm not aware of this particular web builder, I think it is important for other web building platforms to be aware of the attack.

  • This is old news. Disclosed in March, my client's site was hacked in April by this. When would the premium version of WordFence have prevented it?

    • Hi Ken,

      Wordfence Premium has protected against this since March 29. The vulnerability itself may be old news, but there is a quantitative difference between a few hundred attacks a day, which is what we were seeing prior to May 10, and the millions of attacks we've seen since. We feel that this large-scale attack has a substantially higher chance of infecting any remaining unpatched sites than the much lower volume of attacks we were seeing prior to May 10.

  • These are automatic attacks by botnets, as I can see a lot of them blocked by Wordfence on websites without the Tatsu Builder. Anyway thank you for the informations!

  • My sites have been attacked in the past week. The encrypted files containing .sp3ctra_XO.php were intercepted, and quarantined. I have reported the originating IPs to their hosting companies, most of them in EU. HOWEVER: None of my sites use the Tatsu Builder. Wordfence Premium did not recognize any of these attacks, probably because they were intercepted by modsecurity and Configserver CXS before they could reach the website. Which other plugin could be the culprit?

    • Hi Burt,

      These attacks aren't checking to see if Tatsu builder is installed first, they're sending the whole attack, payload and all, at every site they can find, even if no vulnerability is present. This is likely what happened in your case, and you're correct that any attack intercepted before PHP runs (which would happen if Modsecurity blocked the attack) wouldn't be seen by Wordfence.

  • Hi, RAM: Thanks, I could see that. I'm getting countless probes for .sp3ctra_XO.php, even for websites that don't have Wordpress at all. They don't get anywhere, because a custom modsec rule catches the probe, and a permblock is issued. HOWEVER, I have seen cases where /upload/typehub and some subdirs were created. I was under the impression that Tatsu Builder was (ab)used to do that. If no Tatsu is around, what creates those directories and what tries to drop the malware into them? And how can we stop unwanted uploads? A Wordfence facility to limit uploads to certain subdirs (for instance /wp-content/uploads) to certain IPs would be very helpful.

    • Hi Burt,

      Type Hub was a standalone plugin before it got rolled into Tatsu Builder so you may have seen sites with it installed, and it's likely they're still vulnerable. Limiting uploads to certain IPs could potentially impact the functionality of a lot of plugins, but we do have an option in Wordfence already to disable PHP execution on files in wp-content/uploads.

  • Never had Type Hub, never had Tatsu Builder. There must be something else on the loose. PHP execution in uploads is disabled, thank you.

  • As for limiting uploads to certain IPs, I could happily live with optional IP restrictions for /wp-content/uploads. Others probably can't.

  • Excellent Write up!
    Any indications as to what the goal is with the surge of attacks? Just being used as a download location for a dropper?

    • Hi Scott,

      We don't have direct visibility to a lot of infected sites since this wave of attacks would have been blocked on every site using our WAF, but we can make some inferences based on sites we've found the .sp3ctra_XO.php payload on. We're seeing it used to install more full-featured backdoors onto infected sites since it provides multiple methods to do so - it might be more precise to call it an uploader or downloader rather than a dropper. We're also seeing malicious JavaScript used to redirect visitors to a variety of landing pages, including fake PDF downloads and online pharmacies, though we haven't pulled on those threads yet.