Title: EGI SVG 'ADVISORY' [TLP:WHITE] HIGH risk use-after-free privilege
escalation vulnerability in linux kernel [EGI-SVG-CVE-2021-3715]
Date: 2021-09-10
Updated: 2021-10-12
Affected software and risk
==========================
HIGH risk vulnerability concerning the Linux kernel's Traffic Control
networking subsystem.
Package : Linux kernel
CVE ID : CVE-2021-3715
Bug ID : 1993988
A flaw was found in the "Routing decision" classifier in the Linux kernel's
Traffic Control networking subsystem in the way it handled changing of
classification filters, leading to a use-after-free condition.
This flaw allows unprivileged local users to escalate their privileges on the
system. The highest threat from this vulnerability is to confidentiality,
integrity, as well as system availability. [R 1]
Actions required/recommended
============================
Sites which do NOT have recommended mitigation already in place (see below)
which has previously been recommended in order to mitigate and reduce the risk
from various vulnerabilities should update as soon as possible.
Other sites should update as soon as is convenient.
Component installation information
==================================
Note that at present patches are available for RHEL 7 and derivatives, but not
yet for RHEL 8 and derivatives.
Sites running RHEL 8 and RHEL 7 should see [R 1]
Sites running CentOS should also see [R 1]
Sites running Debian should see [R 2]
Sites running Ubuntu should see [R 3]
Sites running Scientific Linux should see [R 4]
Mitigation
==========
Mitigation is possible by disabling unprivileged _network_ namespaces.
In general, we recommend unprivileged _network_ namespaces are disabled, if
they are not required.
Note that this works for Singularity [R 5], thus allowing unprivileged user
namespaces to be kept enabled for Singularity.
However, please note that on RHEL/CentOS 8 and derivatives, there are a few
system services that by default expect network namespaces to work: please check
[R 5] for further information.
More information
================
The EGI Software Vulnerability Group considers this vulnerability 'HIGH' risk
if unprivileged _network_ namespaces are NOT disabled.
TLP and URL
===========
** WHITE information - Unlimited distribution
- see https://go.egi.eu/tlp for distribution restrictions **
URL: https://advisories.egi.eu/Advisory-SVG-CVE-2021-3715
Minor updates may be made without re-distribution to the sites.
Comments
========
Comments or questions should be sent to svg-rat at mailman.egi.eu
If you find or become aware of another vulnerability which is relevant to EGI
you may report it by e-mail to
report-vulnerability at egi.eu
the EGI Software Vulnerability Group will take a look according to the
procedure defined in [R 6].
Note that this is undergoing revision.
References
==========
[R 1] https://access.redhat.com/security/cve/CVE-2021-3715
[R 2] https://security-tracker.debian.org/tracker/CVE-2021-3715
[R 3] https://people.canonical.com/~ubuntu-security/cve/2021/CVE-2021-3715
[R 4] https://scientificlinux.org/category/sl-errata/slsa-20213438-1/
[R 5] https://opensciencegrid.org/docs/worker-node/install-singularity/#enabling-unprivileged-singularity
[R 6] https://documents.egi.eu/public/ShowDocument?docid=3145
Credit
======
SVG was alerted to this vulnerability by Mischa Salle
Timeline
========
Yyyy-mm-dd [EGI-SVG-2021-CVE-2021-3715]
2021-09-09 SVG alerted to this issue by Mischa Salle
2021-09-09 Acknowledgement from the EGI SVG to the reporter
2021-09-09 Investigation of vulnerability and relevance to EGI carried out by
EGI SVG
2021-09-10 EGI SVG Risk Assessment completed
2021-09-10 Advisory sent to sites
2021-10-12 Advisory placed on SVG wiki
Context
=======
This advisory has been prepared as part of the effort to fulfil EGI SVG's
purpose "To minimize the risk to the EGI infrastructure arising from software
vulnerabilities"
The risk is that assessed by the group, according to the EGI SVG issue handling
procedure [R 6] in the context of how the software is used in the EGI
infrastructure. It is the opinion of the group, we do not guarantee it to be
correct. The risk may also be higher or lower in other deployments depending on
how the software is used.
-----------------------------
This advisory is subject to the Creative commons licence
https://creativecommons.org/licenses/by/4.0/ and the EGI https://www.egi.eu/
Software Vulnerability Group must be credited.
------------------------------
Note that the SVG issue handling procedure is currently under review, to take
account of the increasing inhomogeneity of the EGI infrastructure.
On behalf of the EGI SVG,