SolarWinds says it was notified by Microsoft of an actively exploited vulnerability in its Serv-U managed File Transfer Server and Serv-U Secured FTP and are urging customers to install the company’s hotfix immediately.
According to SolarWinds, Microsoft’s research suggests a singlet threat actor was targeting a limited set of customers, although it didn’t elaborate further. However, the company said this exploit is not related to the compromise of its SolarWinds Orion platform that was discovered last December.
The vulnerability, tracked as CVE-2021-35211, is a remote code execution vulnerability that could allow an attacker to gain privileged and run arbitrary code, install programs; view change or delete data; or run programs on the affected system, according to SolarWinds’ advisory.
Customers running the latest Serv-U version 15.2.3 HF1 released May 5, 2021 and all prior versions should apply the hotfix immediately, the company says.
SolarWinds says it does not have an estimate of how many Serv-U customers were impacted and doesn’t know the identity of the victims.
To determine if you have been compromised, the company lists these steps in its advisory:
The following steps are steps you can take to determine if your environment has been compromised:
- Is SSH enabled for your Serv-U installation? If SSH is not enabled in the environment, the vulnerability does not exist.
- Is your environment throwing exceptions? This attack is a Return Oriented Programming (ROP) attack. When exploited, the vulnerability causes the SolarWinds Serv-U product to throw an exception and then intercepts the exception handling code to run commands. Please note, several reasons exist for exceptions to be thrown, so an exception itself is not necessarily an indicator of attack. Please collect the DebugSocketlog.txt log file.
In the log file DebugSocketlog.txt you may see an exception, such as:07] Tue 01Jun21 02:42:58 – EXCEPTION: C0000005; CSUSSHSocket::ProcessReceive(); Type: 30; puchPayLoad = 0x041ec066; nPacketLength = 76; nBytesReceived = 80; nBytesUncompressed = 156; uchPaddingLength = 5Exceptions may be thrown for other reasons so please collect the logs to assist with determining your situation.
- Are you seeing potentially suspicious connections via SSH? Look for connections via SSH from the following IP addresses, which have been reported as a potential indicator of attack by the threat actor:
or, look for connections via TCP 443 from the following IP address: 220.127.116.11
The company will provide more information once customers have had a change to upgrade and apply the hotfix. The update takes only a few minutes, so do this ASAP if you’re running the impacted software.