Google's osconfig agent - local privilege escalation

[Imre Rad <radimre83 () gmail com>]

Osconfig is a beta service by Google, a poll based "desired state
configuration" solution: "You can use the OS configuration management
service to deploy, query, and maintain consistent configurations
(desired state and software) for your VM instance (VM)."
VMs on the Compute Engine have a privileged agent process called
"google_osconfig_agent" running by default.

The agent was vulnerable to local privilege escalation due to relying
on a predictable path inside the /tmp directory. An unprivileged
malicious process could abuse this flaw to win a race condition and
take over the files managed by the high privileged agent process and
thus execute arbitrary commands as the root user (full capabilities).
Exploitation was possible only during an osconfig recipe being
deployed.

Google has fixed this issue recently (2020-09-05); remediation is to
upgrade the process from the OS package repositories. (VMs that were
created since the new version was published, are not affected.)

More info and proof of concept code can be found here:
https://github.com/irsl/google-osconfig-privesc

More info about osconfig:
https://cloud.google.com/compute/docs/os-config-management

Imre

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