Badlock Bug Declared A Bust--But Patch, Anyway

The highly anticipated unveiling today of the Badlock bug in Windows and Samba revealed that the vulnerability was no blockbuster after all, but rather a widespread--and not critical-- vulnerability that can be abused in man-in-the-middle attacks in file server environments.

An attacker could intercept a user’s credentials and steal or modify files, or wage a denial-of-service attack, but he or she would have to be on the same network as the victim, security experts say. The privilege-elevation vulnerability was discovered by Stefan Metzmacher, a member of the Samba development team as well as a Samba developer with SerNet, which provides Samba code packages for Linux products, such as Red Hat Enterprise Server and Novell SUSE Linux Enterprise Server.

Microsoft and Samba both released patches today for Badlock, which is a flaw in Microsoft’s authentication protocols Security Account Manager (SAM) and Local Security Authority (LSAD), which are used with SMB, aka Server Message Block. SMB is a protocol used for shared access to files, printers, serial ports, and communications between client and server machines.

SerNet on March 22 branded and provided a sneak-peek of Badlock with a website as well as its own custom graphic, a move that was widely criticized for giving bad guys a heads up with hints before patches were available for the flaw -- as well as for SerNet’s role as a security vendor that stands to profit from the patch mania following the bug’s big reveal today. And after the details of the bug today confirmed that it was not a critical remote code execution bug as many had predicted, security experts expressed their disappointment and frustration in the buildup surrounding Badlock.

Even so, security experts urged organizations to patch for the flaw (CVE-2016-0128). The flaw was rated as "important" by Microsoft, a far cry from the more serious “critical” level ranking. But given that it’s a bug affecting Windows file servers as well as Unix ones, it should be patched, experts say.

“This is not a pants-on-fire, but a normal, Patch Tuesday that also happens to involve Unix people,” says Tod Beardsley, security research manager for Rapid7. “Remote-code execution would have been a straight shot and that would [have been] a giant disaster.”

Johannes Ullrich, head of the SANS Internet Storm Center, says the hype before the patch was unwarranted. “[It’s] a big let-down. This did not deserve all the hype,” Ullrich says. “’Branded vulnerabilities are great to get people’s attention, but they should not be abused like this. This vulnerability is a MiTM and DoS vulnerability, which isn’t a big deal in the case of SMB, which should never be used across untrusted networks.”

Beardsley characterizes it as a “protocol oddity,” which makes it noteworthy, but in and of itself not especially risky. “The adversary has to be in a privileged position to begin with” to exploit the bug, he says. “I would have to be on the same network as you are. I could compromise your ISP, and be on the same switched network in your building, but I can already do better things [instead] than this [Badlock].”

Security expert Dan Kaminsky says it’s a design flaw that could pose some patching challenges. “It’s a class of flaws that’s not particularly new, but what is new is that Samba is significantly changing a whole bunch of defaults” in the patches, he says. “We don’t want admin credentials plucked off the wire to do arbitrary admin things.”

Patching for Badlock is no “click button” process, Kaminsky says. “This patch more than anything needs to be tested. It may not work in the field, and may not be backwards-compatible,” he says. “When you mess with Windows authentication, fixes at this layer have backwards-compatible issues IT admins have to be aware of.”

SANS’ Ullrich says he doubts patching for Badlock will affect either Samba or Windows’ SMB deployments, but others, such as Apple’s OS X implementation, could be tricky. There aren’t enough details as yet on the how the bug was actually fixed, he says, but “if they had to make the SMB protocol more pedantic about checking authentication, then it is possible that buggy implementations will no longer be able to connect,” he says.

Microsoft, which calls the flaw the Windows SAM and LDAD Downgrade Vulnerability, issued a patch for all supported versions of Windows Vista, Windows Server 2008, Windows 7, Windows Server 2008 R2, Windows 8.1, Windows Server 2012, Windows Server 2012 R2, Windows RT 8.1, and Windows 10.

Samba issued updatesto Samba versions 3.6.x, 4.0.x, 4.1.x, 4.2.0-4.2.9, 4.3.0-4.3.6, and 4.4.0 for Badlock (CVE-2016-2118).

“Obviously, this is not the class of bug people expected,” Kaminsky says. But “this is not nothing,” either.

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