Bug 2012245 (CVE-2021-41133)

Summary: CVE-2021-41133 flatpak: Sandbox bypass via recent VFS-manipulating syscalls
Product: [Other] Security Response Reporter: Guilherme de Almeida Suckevicz <gsuckevi>
Component: vulnerabilityAssignee: Red Hat Product Security <security-response-team>
Status: CLOSED ERRATA QA Contact:
Severity: high Docs Contact:
Priority: high    
Version: unspecifiedCC: amigadave, debarshir, klember, mcatanza
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: flatpak 1.12.1 Doc Type: If docs needed, set a value
Doc Text:
A flaw was found in the flatpak package. It is susceptible to a software flaw that can deceive portals and other host-OS services into treating the flatpak app as an ordinary, non-sandboxed host-OS process. This flaw allows the escalation of privileges that the corresponding services presume the flatpak app has. The highest threat from this vulnerability is to confidentiality, integrity, as well as system availability.
 Story Points: ---
Clone Of: Environment:
Last Closed: 2021-11-01 14:07:50 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On: 2012246, 2012862, 2012864, 2012865, 2012866, 2012867, 2012868, 2012869    
Bug Blocks: 2012248    

Description Guilherme de Almeida Suckevicz 2021-10-08 16:19:32 UTC 
Flatpak is a system for building, distributing, and running sandboxed desktop applications on Linux. In versions prior to 1.10.4 and 1.12.0, Flatpak apps with direct access to AF_UNIX sockets such as those used by Wayland, Pipewire or pipewire-pulse can trick portals and other host-OS services into treating the Flatpak app as though it was an ordinary, non-sandboxed host-OS process. They can do this by manipulating the VFS using recent mount-related syscalls that are not blocked by Flatpak's denylist seccomp filter, in order to substitute a crafted `/.flatpak-info` or make that file disappear entirely. Flatpak apps that act as clients for AF_UNIX sockets such as those used by Wayland, Pipewire or pipewire-pulse can escalate the privileges that the corresponding services will believe the Flatpak app has. Note that protocols that operate entirely over the D-Bus session bus (user bus), system bus or accessibility bus are not affected by this. This is due to the use of a proxy process `xdg-dbus-proxy`, whose VFS cannot be manipulated by the Flatpak app, when interacting with these buses. Patches exist for versions 1.10.4 and 1.12.0, and as of time of publication, a patch for version 1.8.2 is being planned. There are no workarounds aside from upgrading to a patched version.

Reference:
https://github.com/flatpak/flatpak/security/advisories/GHSA-67h7-w3jq-vh4q
Comment 1 Guilherme de Almeida Suckevicz 2021-10-08 16:19:47 UTC 
Created flatpak tracking bugs for this issue:

Affects: fedora-all [bug 2012246]
Comment 4 devthomp 2021-10-11 14:24:36 UTC 
As per link:
https://github.com/flatpak/flatpak/security/advisories/GHSA-67h7-w3jq-vh4q

Patches
The short-term solution is to expand the deny-list of syscalls in the seccomp filter:
e26ac75
89ae9fe
26b1248
a10f52a
9766ee0
4c34815
1330662
462fca2
Comment 8 errata-xmlrpc 2021-11-01 13:35:45 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2021:4042 https://access.redhat.com/errata/RHSA-2021:4042
Comment 9 Product Security DevOps Team 2021-11-01 14:07:50 UTC 
This bug is now closed. Further updates for individual products will be reflected on the CVE page(s):

https://access.redhat.com/security/cve/cve-2021-41133
Comment 10 errata-xmlrpc 2021-11-01 16:32:51 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 7

Via RHSA-2021:4044 https://access.redhat.com/errata/RHSA-2021:4044
Comment 11 errata-xmlrpc 2021-11-02 18:22:52 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8.1 Extended Update Support

Via RHSA-2021:4106 https://access.redhat.com/errata/RHSA-2021:4106
Comment 12 errata-xmlrpc 2021-11-02 20:10:04 UTC 
This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8.2 Extended Update Support

Via RHSA-2021:4107 https://access.redhat.com/errata/RHSA-2021:4107