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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: 0) by Anonymous Coward on Tuesday July 04 2017, @06:37PM (1 child)

    by Anonymous Coward on Tuesday July 04 2017, @06:37PM (#534873)

    ^ found the Technical Thug

    SITUATION: OS upgrade.

            TECHNICAL THUG: Reads source code of new release, takes only what he likes. []

    If you're going to argue that you don't have a monoculture because you can hack your kernel, then you can hack systemd also. The premise in the subject line is invalid, and the topic of discussion is moot.

    Don't like how systemd Gives Root Privileges to Invalid Usernames? Fix it yourself, Thug!

  • (Score: 2) by Runaway1956 on Wednesday July 05 2017, @12:08AM

    by Runaway1956 (2926) Subscriber Badge on Wednesday July 05 2017, @12:08AM (#534981) Homepage Journal

    The argument against systemd seems to run more along the lines, "systemd is, in and of itself a hack, and a solution searching for a problem that doesn't exist". I'm not really on either side of that argument. I'm the eternal skeptic, who saw little need for systemd, but was willing to give it a try. But I keep hearing more and more arguments against systemd that make sense. Now, we have a potential security flaw that makes systemd even less appealing.

    Further, there are a number of posts that indicate that systemd is more of a political solution to corporate problems, than it is a software solution to init problems.

    Hail to the Nibbler in Chief.