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Linux systemd Gives Root Privileges to Invalid Usernames

posted by Fnord666 on Monday July 03 2017, @10:12PM   Printer-friendly
from the it's-a-feature dept.

MrPlow writes:

Submitted via IRC for TheMightyBuzzard

A bug in Linux's systemd init system causes root permissions to be given to services associated with invalid usernames, and while this could pose a security risk, exploitation is not an easy task.

A developer who uses the online moniker "mapleray" last week discovered a problem related to systemd unit files, the configuration files used to describe resources and their behavior. Mapleray noticed that a systemd unit file containing an invalid username – one that starts with a digit (e.g. "0day") – will initiate the targeted process with root privileges instead of regular user privileges.

Systemd is designed not to allow usernames that start with a numeric character, but Red Hat, CentOS and other Linux distributions do allow such usernames.

"It's systemd's parsing of the User= parameter that determines the naming doesn't follow a set of conventions, and decides to fall back to its default value, root," explained developer Mattias Geniar.

While this sounds like it could be leveraged to obtain root privileges on any Linux installation using systemd, exploiting the bug in an attack is not an easy task. Geniar pointed out that the attacker needs root privileges in the first place to edit the systemd unit file and use it.

[...] Systemd developers have classified this issue as "not-a-bug" and they apparently don't plan on fixing it. Linux users are divided on the matter – some believe this is a vulnerability that could pose a serious security risk, while others agree that a fix is not necessary.

See, this is why we can't have nice init systems.

Source: http://www.securityweek.com/linux-systemd-gives-root-privileges-invalid-usernames

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  • (Score: 2) by mcgrew on Tuesday July 04 2017, @05:31PM (4 children)

    by mcgrew (701) <publish@mcgrewbooks.com> on Tuesday July 04 2017, @05:31PM (#534848) Homepage Journal

    Original source of that quote: me. Glad to see it being used!

    --
    mcgrewbooks.com mcgrew.info nooze.org
    Starting Score:    1  point
    Karma-Bonus Modifier   +1  
    Total Score:   2  

  • (Score: 1) by khallow on Wednesday July 05 2017, @04:36AM (3 children)

    by khallow (3766) Subscriber Badge on Wednesday July 05 2017, @04:36AM (#535055) Journal
    I heard the saying from Baldrson [slashdot.org] (of Slashdot fame) around 2001-2003 when I roomed with him. We were trying out some cell automata-based prisoners' dilemma games at the time (bottom line: the more mobile the automata, the more advantage that defection has over cooperation). I gather it's likely an independent coining of the term.

    • (Score: 2) by mcgrew on Wednesday July 05 2017, @02:48PM (2 children)

      by mcgrew (701) <publish@mcgrewbooks.com> on Wednesday July 05 2017, @02:48PM (#535206) Homepage Journal

      That was shortly after I said it, and yes, it was on slashdot. I call it "mcgrew's razor" although I should probably misspell "mcgrew", because Hanlon's Razor is allegedly from a Robert Heinlein story.

      --
      mcgrewbooks.com mcgrew.info nooze.org

      • (Score: 1) by khallow on Friday July 07 2017, @03:40AM (1 child)

        by khallow (3766) Subscriber Badge on Friday July 07 2017, @03:40AM (#535993) Journal
        Then he may well have heard it from you. My take is that he has been obsessed with these ideas since the late 70s or early 80s, and has read a fair bit of Heinlein in his youth. So I can't rule out an independent coining of the term.