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Article from Issue 179/2015

Updates on technologies, trends, and tools

Weird Security Flaw Affected Intel Chips for 16 Years

At the BlackHat conference in Las Vegas, Battelle security researcher Christopher Domas revealed a hidden security flaw that affected Intel processors for 16 years. The first flawed chips appeared in 1995, and the problem wasn't fixed until the 2011 crop of new processors that included the Sandy Bridge series.

The strange problem occurs at such a deep level of the hardware architecture that it is unstoppable and undetectable by the operating system. Intel processors have a privilege ring architecture that defines the level of privilege available to a process. As most developers and power users know, the kernel occupies Ring 0, usermode applications live at Ring 3, and device drivers fall somewhere in between. Far lesser known are the mysterious rings inside of Ring 0. Ring -1 is the hypervisor ring, which manages the operating systems running at Ring 0, and below that, the murky Ring -2 is home to Intel's System Management Mode software. This innermost ring is loaded by the system firmware, and it is effectively untouched by the rest of the system. The bug that affected Intel processors for 16 years allowed privilege escalation code to run at Ring -2, where it was invisible to the rest of the system.

Users with older PCs should watch for more news on this problem, but it doesn't look like a quick fix will appear anytime soon, and now that the flaw has been published in the press, it is only a matter of time before intruders exploit it. Linux users better not bet on that natural security of Linux systems to get you through this one: The operating system is just another app when you're down in Ring -2.

OpenSSH 7.0 Secure Shell Arrives

The OpenSSH project has announced OpenSSH 7.0, a major new release that addresses several security issues associated with previous versions. According to the announcement by OpenSSH developer Damien Miller, the focus of the new release is "to deprecate weak, legacy, and/or unsafe cryptography."

Some of the problems fixed with the new release include:

  • OpenSSH 6.8 and 6.9 incorrectly made TTYs world-writable.
  • The Portable SSH variant had a privilege escalation issue related to PAM support.
  • Previous editions allow an attacker to circumvent MaxAuthTries using keyboard-interactive authentication.

New features available with this release include improvements to public key types and ciphers, as well as a new prohibit-password setting. OpenSSH 7.0 also comes with several bug fixes for better security and improved usability. OpenSSH is maintained by the OpenBSD project. Watch your distro's app repository for soon-to-arrive OpenSSH 7.0 binary packages.

Qemu Flaw Lets the Guest Escape

The Xen project has announced a bug (CVE-2015-5154) that allows a process running inside a Qemu virtual machine to escalate its privileges to the privilege level of the Qemu process. This exploit basically lets the guest process escape to the privileges of the host.

The attack uses the Qemu emulated IDE CDROM device. According to the Xen project, "All Xen systems running x86 HVM guests without stubdomains that have been configured with an emulated CD-ROM driver model are vulnerable."

See the security page for your Linux vendor for more on how to fix the problem. The best advice is to avoid using an emulated CD-ROM device with Qemu until you have taken the necessary steps and installed the patch.

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