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

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.


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  • (Score: 3, Interesting) by Runaway1956 on Wednesday July 05 2017, @12:02AM

    by Runaway1956 (2926) Subscriber Badge on Wednesday July 05 2017, @12:02AM (#534978) Homepage Journal

    Alright. I thought, "Fair question." Then, I thought, "No, actually, that's not just a fair question, it's a good question."

    I guess I'm comparing Linux to Windows, which is a true monoculture. You take whatever Microsoft offers, and that's it. And, Microsoft intends for everyone to upgrade to Windows 10, and all older kernels and versions are to just die off. Proprietary is proprietary, and that side of the computing world is as monoculture as possible.

    With Linux, many tweaks are documented. You can compile your kernel to be as mathematically precise as humanly possible, or you can compile it with much looser parameters. Linus and his people do, as you suggest, develop in a path, with a vision, and the Linux world mostly follows along. A quick search you may find interesting, or not - []

    The thing about the Linux community, is that a heretic can openly distribute whatever hacks he has made to Linus' kernel. There are no secretive forums, operating under threat of discovery by Linus and a horde of lawyers. A developer can claim to have created a "Better Linux Kernel", and flaunt his work openly, for all the world to see, and use. []

    And, it hasn't taken me very long to alter my own viewpoint a little. Doing a quick search comparing BSD kernels to Linux kernels leads to several discussions - I'll just throw the search out here, and you may dive in, or not, as you wish - []

    You may make an argument that all Unix-like kernels are part of a monoculture, I suppose. With Unix, Ma Bell created a pretty damned good operating system. And, all of the "best" OS's tend to emulate Unix. You tell me - does that make it a monoculture, or not?

    Don’t confuse the news with the truth.
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