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'Most Serious' Linux Privilege-Escalation Bug Ever Is Under Active Exploit (arstechnica.com)

Posted by msmash on from the linux-security-flaws dept.

Reader operator_error shares an ArsTechnica report: A serious vulnerability that has been present for nine years in virtually all versions of the Linux operating system is under active exploit, according to researchers who are advising users to install a patch as soon as possible. While CVE-2016-5195, as the bug is cataloged, amounts to a mere privilege-escalation vulnerability rather than a more serious code-execution vulnerability, there are several reasons many researchers are taking it extremely seriously. For one thing, it's not hard to develop exploits that work reliably. For another, the flaw is located in a section of the Linux kernel that's a part of virtually every distribution of the open-source OS released for almost a decade. What's more, researchers have discovered attack code that indicates the vulnerability is being actively and maliciously exploited in the wild.

"It's probably the most serious Linux local privilege escalation ever," Dan Rosenberg, a senior researcher at Azimuth Security, told Ars. "The nature of the vulnerability lends itself to extremely reliable exploitation. This vulnerability has been present for nine years, which is an extremely long period of time." The underlying bug was patched this week by the maintainers of the official Linux kernel. Downstream distributors are in the process of releasing updates that incorporate the fix. Red Hat has classified the vulnerability as "important."

3 of 109 comments (clear)

  1. Root my Android phone? by crow · · Score: 5, Interesting

    Can I use this to root my Android phone? I just want to install an ad-blocking /etc/hosts file, so I don't need a permanent root. This sounds like just the sort of exploit to do the trick, but I haven't looked at the technical details. I just want to do this before the next security update patches it.

  2. Re:Should have used APPS! by Aighearach · · Score: 1, Interesting

    Can someone explain this bug in English?

    There is a thing called COW (copy on write). There is a bug where worker code can ride the cow over the fence and gain access to the farmer's private yard.

    Moral of the story: Don't let people ride your cows, let them find their own darn *nix shell.

    Or more literal version: People with user access can get administrator access without permission.

  3. Most Popular Comment @ Ars by CrashNBrn · · Score: 3, Interesting
    S2pidiT Ars Centurion said:

    Linus explained on the GitHub link:

    This is an ancient bug that was actually attempted to be fixed once (badly) by me eleven years ago in commit 4ceb5db9757a ("Fix get_user_pages() race for write access") but that was then undone due to problems on s390 by commit f33ea7f404e5 ("fix get_user_pages bug").

    In the meantime, the s390 situation has long been fixed, and we can now fix it by checking the pte_dirty() bit properly (and do it better). The s390 dirty bit was implemented in abf09bed3cce ("s390/mm: implement software dirty bits") which made it into v3.9. Earlier kernels will have to look at the page state itself.

    Also, the VM has become more scalable, and what used a purely theoretical race back then has become easier to trigger.

    To fix it, we introduce a new internal FOLL_COW flag to mark the "yes, we already did a COW" rather than play racy games with FOLL_WRITE that is very fundamental, and then use the pte dirty flag to validate that the FOLL_COW flag is still valid.

    So there was an attempt to fix the race condition over a decade ago, but it got undone.