Bug 1675070 (CVE-2019-8308) - CVE-2019-8308 flatpak: potential /proc based sandbox escape
Summary: CVE-2019-8308 flatpak: potential /proc based sandbox escape
Alias: CVE-2019-8308
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
Depends On: 1675432 1675433 1675435 1675776
Blocks: 1674941
TreeView+ depends on / blocked
Reported: 2019-02-11 18:50 UTC by Scott Gayou
Modified: 2021-02-16 22:23 UTC (History)
2 users (show)

Fixed In Version: flatpak 1.2.3, flatpak 1.0.7
Doc Type: If docs needed, set a value
Doc Text:
A flaw was found in flatpak. In certain special cases, installing flatpak applications and runtimes system-wide may allow an attacker to escape the flatpak sandbox. The highest threat from this vulnerability is to data confidentiality and integrity as well as system availability.
Clone Of:
Last Closed: 2019-06-10 10:47:40 UTC

Attachments (Terms of Use)

System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHSA-2019:0375 0 None None None 2019-02-19 17:41:55 UTC

Description Scott Gayou 2019-02-11 18:50:37 UTC
A flaw was discovered that may allow an attacker to escape from the flatpak sandbox via /proc/self/exe.

Upstream Commit: 

Comment 2 Scott Gayou 2019-02-11 20:57:18 UTC
Created flatpak tracking bugs for this issue:

Affects: fedora-all [bug 1675432]

Comment 5 Scott Gayou 2019-02-12 19:50:50 UTC
My current understanding is that the only portion of flatpak that should run as root is the system-helper. The system-helper functionality may call into apply_extra_data(), which eventually calls flatpak_run_setup_base_argv. The patch adds a new flag, FLATPAK_RUN_FLAG_NO_PROC, to ensure that proc isn't reachable during this operation.

From the devs (paraphrasing) -- this (running as root) should only happen during installation to a system-wide repository. Thus, users running an app or installing into a user repository should be not be impacted by this flaw as those specific operations should not occur as root.

Comment 6 Scott Gayou 2019-02-12 21:07:19 UTC
Looks like the potential callflow for the vulnerability is handle-deploy signal (unsure who actually raises this signal) inside of flatpack_system_helper.c -> flatpak_dir_deploy_install -> flatpak_dir_deploy -> apply_extra_data -> flatpak_run_setup_base_argv. The patch adds the  FLATPAK_RUN_FLAG_NO_PROC flag to this call.

flatpak_run_setup_base_argv also seems to be called in flatpak_run_app without the flag explicitly set. It looks like this instance could be executed via flatpak_installation_launch_full, but system-helper doesn't appear to call into that.

The question is if system-helper can ever trigger flatpak_run_app as root without that flag set, and, after a quick look, I don't think it can.

Comment 8 Scott Gayou 2019-02-13 16:06:29 UTC
Looks like Debian got CVE-2019-8308 assigned: https://github.com/flatpak/flatpak/issues/2699

Comment 9 Scott Gayou 2019-02-13 16:11:10 UTC

This flaw appears to impact systems in special cases involving installing flatpak applications and runtimes system-wide. Installation of flatpak applications and runtimes locally should not be impacted.

Comment 11 errata-xmlrpc 2019-02-19 17:41:55 UTC
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2019:0375 https://access.redhat.com/errata/RHSA-2019:0375

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