Title: EGI SVG 'ADVISORY' [TLP:WHITE] CRITICAL risk - Linux kernel
vulnerability affecting RHEL/CentOS 8 and derivatives
[EGI-SVG-CVE-2021-22555]
Date: 2021-07-28
Updated: 2021-08-12, 2021-08-18, 2021-09-01, 2021-10-06
Affected software and risk
==========================
CRITICAL risk vulnerability concerning linux kernel RHEL/CentOS 8 and
derivatives.
Package : linux kernel
CVE ID : CVE-2021-22555
Bug ID : Red Hat Bugzilla – Bug 1980101
A vulnerability has been found in the linux kernel where an out-of bounds write
in xt_compat_target_from_user() in net/netfilter/x_tables.c allows a local user
to gain privileges or cause a DoS through user name space. [R 1] [R 2] [R 3]
**UPDATE 2021-09-01**
This has now been fixed for RHEL 7, CentOS 7 and other derivatives including
Scientific Linux.
Previously 2021-08-18 it was stated that it had been fixed in Scientific Linux
but this announcement had been made in error.
**UPDATE 2021-08-12**
This has been fixed for RHEL/CentOS 8 and derivatives.
Actions required/recommended
============================
**UPDATE 2021-08-12**
Sites running RHEL/CentOS 8 or derivatives MUST be either patched or have
mitigation in place or software removed by 2021-09-02 00:00 UTC.
Sites failing to act and/or failing to respond to requests from the EGI CSIRT
team risk site suspension.
**UPDATE 2021-09-01**
Sites running RHEL/CentOS 7 or derivatives are recommended to update the
relevant kernel packages as soon as they reasonably can.
Component installation information
==================================
Sites running RHEL 8 and RHEL 7 should see [R 2]
Sites running CentOS8 should also see [R 2]
Sites running Debian should see [R 7]
Sites running Ubuntu should see [R 8]
Sites running Scientific Linux should see [R 9]
Affected software details
=========================
A public Proof Of Concept exploit has been released for RHEL/CentOS 8 and
derivatives.
For RHEL/CentOS 8 and it's derivatives this vulnerability is considered
'CRITICAL' risk.
Members of the Software Vulnerability Group and others have carried out some
testing, and have not been able to execute the Proof Of Concept exploit for
RedHat 7.
We still consider this vulnerability to be 'HIGH' risk for RedHat 7 and its
derivatives.
Mitigation
==========
For hosts which do not need to run user containers, mitigation is possible as
defined in [R 2] by disabling user namespaces, which may not be suitable for
some services.
In general, we recommend unprivileged _network_ namespaces are disabled, if
they are not required [R 5].
Note that this works for Singularity [R 4], 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 4] for further information.
In general, the running of containers (e.g. through Docker) is incompatible
with the mitigation options considered so far.
A different mitigation would be to limit access to vulnerable hosts as much as
feasible.
TLP and URL
===========
** WHITE information - Unlimited distribution - see
https://go.egi.eu/tlp for distribution restrictions **
URL: https://advisories.egi.eu/Advisory-SVG-CVE-2021-22555
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://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2021-22555
[R 2] https://access.redhat.com/security/cve/CVE-2021-22555
[R 3] https://bugzilla.redhat.com/show_bug.cgi?id=1980101
[R 4] https://opensciencegrid.org/docs/worker-node/install-singularity/#enabling-unprivileged-singularity
[R 5] https://advisories.egi.eu/Advisory-SVG-CVE-2020-25211
[R 6] https://documents.egi.eu/public/ShowDocument?docid=3145
[R 7] https://security-tracker.debian.org/tracker/CVE-2021-22555
[R 8] https://people.canonical.com/~ubuntu-security/cve/2021/CVE-2021-22555
[R 9] https://scientificlinux.org/category/sl-errata/slsa-20213327-1/
Timeline
========
Yyyy-mm-dd [EGI-SVG-CVE-2021-22555]
2021-07-25 Investigation of vulnerability and relevance to EGI carried out by
SVG members and Dave Dykstra
2021-07-26 EGI SVG Risk Assessment completed
2021-07-28 Advisory sent to sites to carry out mitigating action in some
circumstances
2021-08-12 Update as fixed for RHEL/CentOS 8 and derivatives
2021-08-18 Update as fixed for Scientific Linux (which turned out not to be!)
2021-09-01 Update as fixed for RHEL 7, CentOS7, and Scientifc Linux.
2021-10-06 Placed on the EGI 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,