Microsoft: We Detect 77,000 Web Shells Each Month

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Microsoft has warned that inadequate security on web applications and internet-facing servers is allowing hackers to use web shells in their tens of thousands each month to launch attacks.

Web shells are pieces of malicious code typically implanted onto web servers to execute commands, steal data and help hackers launch additional raids on the victim organization, such as watering hole attacks.

Microsoft claimed in a new blog this week that thanks to poor IT security hygiene, the use of these tools is rocketing: the tech giant detects around 77,000 each month on an average of 46,000 machines.

“Aside from exploiting vulnerabilities in web applications or web servers, attackers take advantage of other weaknesses in internet-facing servers. These include the lack of the latest security updates, anti-virus tools, network protection, proper security configuration and informed security monitoring,” it continued.

“Interestingly, we observed that attacks usually occur on weekends or during off-hours, when attacks are likely not immediately spotted and responded to.”

Multi-layered protection is needed to mitigate the threat of web shells, beginning with gaining visibility into internet-facing servers by monitoring web application directories for web script file writes, the firm advised.

Regular audits of web server logs, prompt patching, intrusion prevention to stop C&C communications, limiting privileged accounts and closing non-standard ports can also help, said Microsoft.

Ilia Kolochenko, founder & CEO of web security company ImmuniWeb, explained that web shells have existed for over a decade and are often automated by hackers, but finding them should not be difficult.

“Usually, once a web shell is uploaded, it is fairly simple to root the server by exploiting unpatched vulnerabilities or its insecure configuration,” he added.

“Detection of web shells is a fairly routine operation, moreover, such attacks are usually attributable to junior hackers unskilled or careless enough to upload a web shell without obfuscation and proper removal after backdooring the server.”

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