Ransomware attackers quickly weaponize PHP vulnerability with 9.8 severity rating

In a post published Friday, Censys researchers said that the exploitation by the TellYouThePass gang started on June 7 and mirrored past incidents that opportunistically mass scan the Internet for vulnerable systems following a high-profile vulnerability and indiscriminately targeting any accessible server. The vast majority of the infected servers have IP addresses geolocated to China, Taiwan, Hong Kong, or Japan, likely stemming from the fact that Chinese and Japanese locales are the only ones confirmed to be vulnerable, Censys researchers said in an email.

Since then, the number of infected sites—detected by observing the public-facing HTTP response serving an open directory listing showing the server’s filesystem, along with the distinctive file-naming convention of the ransom note—has fluctuated from a low of 670 on June 8 to a high of 1,800 on Monday.

Censys researchers said in an email that they’re not entirely sure what’s causing the changing numbers.

“From our perspective, many of the compromised hosts appear to remain online, but the port running the PHP-CGI or XAMPP service stops responding—hence the drop in detected infections,” they wrote. “Another point to consider is that there are currently no observed ransom payments to the only Bitcoin address listed in the ransom notes (source). Based on these facts, our intuition is that this is likely the result of those services being decommissioned or going offline in some other manner.”

XAMPP used in production, really?

The researchers went on to say that roughly half of the compromises observed show clear signs of running XAMPP, but that estimate is likely an undercount since not all services explicitly show what software they use.

“Given that XAMPP is vulnerable by default, it’s reasonable to guess that most of the infected systems are running XAMPP,” the researchers said. This Censys query lists the infections that are explicitly affecting the platform. The researchers aren’t aware of any specific platforms other than XAMPP that have been compromised.

The discovery of compromised XAMPP servers took Will Dormann, a senior vulnerability analyst at security firm Analygence, by surprise because XAMPP maintainers explicitly say their software isn’t suitable for production systems.

“People choosing to run not-for-production software have to deal with the consequences of that decision,” he wrote in an online interview.

While XAMPP is the only platform confirmed to be vulnerable, people running PHP on any Windows system should install the update as soon as possible. The Imperva post linked above provides IP addresses, file names, and file hashes that administrators can use to determine whether they have been targeted in the attacks.