Shellshock Still in the Crosshairs

Old bugs die hard: the three-year-old Shellshock vulnerability was the most commonly targeted security hole in the second quarter of 2017, according to security firm eSentire.

The GNU Bash Remote Code Execution flaw, aka Shellshock (CVE-2014-6271), accounted for 40% of the top eight flaws targeted in Q2, according to new data from eSentire gathered from some 1,500 of its network and host sensors installed in 600 customer sites.

Viktors Engelbrehts, director of threat intelligence at eSentire, says the exposed systems his firm spotted being probed for the flaw are mainly public-facing Web servers.

The critical flaw in Linux and Unix operating systems, as well as Mac OS X, was first discovered in September of 2014, and continues to be left unpatched in many organizations.

That makes it a lucrative target for attackers. Engelbrehts theorizes that the Shellshock-probing activity spotted by his firm likely is the handiwork of state-sponsored attackers gathering intel on vulnerable systems, given the automated, wide range of the scope of the scans.

"Those scanners are fingerprinting" systems on the Internet, he says of eSentire's findings. "Not all of these events necessarily lead to further incidents. But if these assets are vulnerable and the bad guys know about it, they can launch devastating attacks" on widespread systems, he says.

State-sponsored actors such as those out of China are among the types of threat actors conducting such scans for intel they could use in mass attacks, he says.

"We suspect it's mostly Linux, and some Mac [systems] affected," he says.

eSentire also spotted attackers scanning for servers with the Apache Struts CVE-2017-5638 remote code flaw, the Windows CVE-2012-0152 Remote Desktop Protocol bug, and the Windows RDP remote administration flaw (CVE-2001-0540).

Shellshock/Bash is a shell widely used in versions of Linux and Unix, and when exploited, it allows an attacker to run malicious code remotely on a targeted system.

Why does it remain unpatched in so many servers? "I suspect that a lot of organizations are applying compensating controls instead of mitigating the root cause," he says. They're beefing up IDS/IPS systems and blocking signatures, but leaving the hole unpatched, he says.

Shellshock is an especially popular flaw to target mainly because it's so easy to exploit, notes Theresa Payton, CEO of Fortalice Solutions. Payton says her firm mostly finds it unpatched in printers, appliances, and voice systems.

The decision not to patch a server typically has to do with downtime trumping risk. "Patches break things," Payton says, noting that that's why organizations with high uptime requirements sometimes shy away from applying some patches. "But patching strategically is vitally important. You shouldn't use the excuse that it will break things."

Even large organizations can be hit unawares by an attacker gathering intel. Payton's firm has seen this firsthand in penetration-test engagements: "You would be amazed at how many Fortune 100s where we were able to do a vulnerability scan undetected. Their radars didn't pick up that we were scanning their systems," she says.

eSentire's Engelbrehts, meanwhile, says the attackers behind the recent wave of mass Shellshock scans appear to have an automated infrastructure in place to search for these types of flaws en masse.

"It's indiscriminate," he says. "They are clearly using weaknesses as an information-gathering point at massive scale. What scares me most is the volume is really scary" and could be used to wage widespread attacks across multiple organizations and industries, according to Engelbrehts.

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