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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.

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


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  • (Score: 2) by Thexalon on Tuesday July 04 2017, @05:57PM

    by Thexalon (636) on Tuesday July 04 2017, @05:57PM (#534857)

    The argument amounts to: After all this effort, what's been accomplished is replacing possibly-complex shell scripts that work with really complex C that doesn't always work.

    For example, I have rendered a systemd-based box unbootable by unplugging the USB mouse that it expected to have. That isn't the correct behavior: The correct behavior, which other init systems do just fine, is to bring up the box with everything but the mouse, at which point I can do something useful.

    And the "LP sucks" arguments have to do with a repeated pattern of serious and significant bug reports getting a routine response of "WONTFIX - not a bug". On critical system software, that is unacceptable.

    --
    The only thing that stops a bad guy with a compiler is a good guy with a compiler.
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