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23-Year-Old X11 Server Security Vulnerability Discovered

Posted by Unknown on from the stack-smashing-for-fun-and-profit dept.

An anonymous reader writes "The recent report of X11/X.Org security in bad shape rings more truth today. The X.Org Foundation announced today that they've found a X11 security issue that dates back to 1991. The issue is a possible stack buffer overflow that could lead to privilege escalation to root and affects all versions of the X Server back to X11R5. After the vulnerability being in the code-base for 23 years, it was finally uncovered via the automated cppcheck static analysis utility." There's a scanf used when loading BDF fonts that can overflow using a carefully crafted font. Watch out for those obsolete early-90s bitmap fonts.

6 of 213 comments (clear)

  1. Many eyes... by Anonymous Coward · · Score: 5, Insightful

    ...looking elsewhere.

    1. Re:Many eyes... by Bacon+Bits · · Score: 5, Funny

      With enough Perl, all eyes are bleeding.

      --
      The road to tyranny has always been paved with claims of necessity.
  2. Re:Privilege escalation is to the server credentia by 10101001+10101001 · · Score: 5, Informative

    Did you actually even bother checking this? No, most modern X11 servers run as root so they can* have hardware access to GLX and DRM. But, please tell me, which distro or OS do you run that runs your X11 server as non-root? Because I'd love to use a system like that.

    *Technically, privilege separation is quite possible on these points, which has been done in OpenBSD AFAIK, but very few people use OpenBSD and I think the whole point of your post was about what the vast majority of people use. Otherwise, you're just quibbling over the point without stating it that most people don't run a "modern" X11 server.

    --
    Eurohacker European paranoia, gun rights, and h
  3. Re:scary by buchner.johannes · · Score: 5, Insightful

    Given that you need to be using obsolete 90s bitmap fonts for this to be an issue, and that X11/X.org is never run as root, I'm not sure that "scary" is the word for this (there's a reason it hasn't come up before in the 23 years since it was introduced).

    Correct in principle, except for two remarks:

    • X runs as root, and has always. Just like getty.
    • If you craft a new bitmap font, running "xset fp+" as a user has the potential to gain you root privileges.

    So yes, not "scary". Just a critical security bug.

    --
    NB: The message above might reflect my opinion right now, but not necessarily tomorrow or next year.
  4. Re:The usual clueless submission... by peppepz · · Score: 5, Informative

    Those fonts are read by fontconfig and freetype, while the bug is in the server-side font support, the one where you must run mkfontdir and possibly edit Xorg.conf to install new fonts. I don't think any distribution allows non-root users to do that.

  5. Re:scary by PPH · · Score: 5, Insightful

    Right. And this is why its so important to have the source code available. Some argue, "Who actually looks at this stuff?" Well, here's an example of someone who did. Not in the classical sense of some aspie code geek reading it by hand. But just feed it to some automated tools and see what pops out.

    --
    Have gnu, will travel.