Information

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Advisory

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256

 Xen Security Advisory CVE-2022-42311,CVE-2022-42312,CVE-2022-42313,CVE-2022-42314,CVE-2022-42315,CVE-2022-42316,CVE-2022-42317,CVE-2022-42318 / XSA-326
                                                                        version 4

         Xenstore: guests can let run xenstored out of memory

UPDATES IN VERSION 4
====================

Public release.

ISSUE DESCRIPTION
=================

Malicious guests can cause xenstored to allocate vast amounts of memory,
eventually resulting in a Denial of Service (DoS) of xenstored.

There are multiple ways how guests can cause large memory allocations
in xenstored:

- - by issuing new requests to xenstored without reading the responses,
  causing the responses to be buffered in memory

- - by causing large number of watch events to be generated via setting up
  multiple xenstore watches and then e.g. deleting many xenstore nodes
  below the watched path

- - by creating as many nodes as allowed with the maximum allowed size and
  path length in as many transactions as possible

- - by accessing many nodes inside a transaction

IMPACT
======

Unprivileged guests can cause a DoS of xenstored, resulting in the
inability to create new guests or modify the configuration of running
guests.

VULNERABLE SYSTEMS
==================

All Xen versions are vulnerable.

Both Xenstore implementations (C and Ocaml) are vulnerable.

MITIGATION
==========

There is no mitigation available.

CREDITS
=======

This issue was discovered by Julien Grall of Amazon.

RESOLUTION
==========

Applying the appropriate attached patches resolve this issue.

Note that the final oxenstored patch (7 or 8, as applicable) is limiting
the security support for oxenstored to trusted driver domains only.

C xenstored Patches 15 and 16 are not part of the XSA, but are useful
for administrators to change current xenstored quota settings and to
audit per-guest resource usage in xenstored.

Note that the patches are based on top of the patches for XSA-414 and
XSA-415. There is a subtle dependency on XSA-419, which can't be resolved
easily, so the patches of XSA-326 should always be applied together with
those of XSA-419.

Note that patches for released versions are generally prepared to
apply to the stable branches, and may not apply cleanly to the most
recent release tarball.  Downstreams are encouraged to update to the
tip of the stable branch before applying these patches.

xsa326/xsa326-xenstored-??.patch           xen-unstable
xsa326/xsa326-oxenstored-??.patch          xen-unstable
xsa326/xsa326-4.16-xenstored-??.patch      Xen 4.16.x
xsa326/xsa326-4.16-oxenstored-??.patch     Xen 4.16.x
xsa326/xsa326-4.15-xenstored-??.patch      Xen 4.15.x
xsa326/xsa326-4.15-oxenstored-??.patch     Xen 4.15.x
xsa326/xsa326-4.14-xenstored-??.patch      Xen 4.14.x
xsa326/xsa326-4.14-oxenstored-??.patch     Xen 4.14.x
xsa326/xsa326-4.13-xenstored-??.patch      Xen 4.13.x
xsa326/xsa326-4.13-oxenstored-??.patch     Xen 4.13.x

$ sha256sum xsa326* xsa326*/*
fbeb48f2137ead7e933d487b95d819b4adec29e33141655dfb40e66861f8d005  xsa326.meta
5da5e9d053a51faba9a553970d53736b333ce713793ed3cf3fefc19943a3ba3d  xsa326/xsa326-4.13-oxenstored-01.patch
6c65b043f5a9a8963c74b22df2187be7936c1228b1dee7b3cd32ea2f207520d0  xsa326/xsa326-4.13-oxenstored-02.patch
f04f4c29f8a63ff7f08af4d9a99b5da9c44eface3523e2dd9da7119d85445d42  xsa326/xsa326-4.13-oxenstored-03.patch
438ddd4a5fb1b4c9bb5bc911052cbb84b3fbe2ce4c2559ec112b7e9cd6c3c436  xsa326/xsa326-4.13-oxenstored-04.patch
e57d98b53c5b03e34a2e554097b634bbf568d9e336ee0ef7ec703d3ff153dd8a  xsa326/xsa326-4.13-oxenstored-05.patch
0b13429993ab1bb5a2a58edeeebfc8bc50987e5d86dddfd6f7108259c31aed97  xsa326/xsa326-4.13-oxenstored-06.patch
e5c995a8eeea776e57c9878b612f17f2d8cad2538897d8cf385a9f9570ecd076  xsa326/xsa326-4.13-oxenstored-07.patch
247d2461b80884a1bbc063074b89beb769243f82f0de61fe0a45fb438b4a6d38  xsa326/xsa326-4.13-oxenstored-08.patch
928c1b4d624b73fab33af936ba520402d0010956939ed4f17f42c8a476e7dd02  xsa326/xsa326-4.13-xenstored-01.patch
4918eab37b70914a01b3277d83d56a20a877982fac8c5c9533afcdc8c16c4123  xsa326/xsa326-4.13-xenstored-02.patch
1b2df2030bbb91729b16174026127f1a056e011814e2c0b14e6b9430c00f6c41  xsa326/xsa326-4.13-xenstored-03.patch
e05aec57d8cdc1f3151cf6a2cfd8fdf10b9776e3ba564ff934d1dd51692c2f12  xsa326/xsa326-4.13-xenstored-04.patch
197e76c74166fc686fd5b1faf6e025abd9a3e1019ebc7954f63d3561b50aa13c  xsa326/xsa326-4.13-xenstored-05.patch
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1aa1458b82fac3b1dbf71f0ad2d8f29203e95ffc8bbe61e3f8aa0895613cb5f8  xsa326/xsa326-4.13-xenstored-13.patch
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6fdd871d77b699fbb4df8efc18fd772131a216e9ac9387832ae66a3af6d58e07  xsa326/xsa326-xenstored-13.patch
49a22d518921be7688cbe5dced9c842b3f0c67f678f3d113bbe5fce36a59d775  xsa326/xsa326-xenstored-14.patch
a8ef297722bb4c5778d3e0f80ab16cdb6024cdb3a349789182d2167409cf1aa2  xsa326/xsa326-xenstored-15.patch
bf20cd4808cba1506ed7404af050d9b05619b48d2d8eda7e166050540b8f25e2  xsa326/xsa326-xenstored-16.patch
$

DEPLOYMENT DURING EMBARGO
=========================

Deployment of the patches and/or mitigations described above (or
others which are substantially similar) is permitted during the
embargo, even on public-facing systems with untrusted guest users and
administrators.

But: Distribution of updated software is prohibited (except to other
members of the predisclosure list).

Predisclosure list members who wish to deploy significantly different
patches and/or mitigations, please contact the Xen Project Security
Team.


(Note: this during-embargo deployment notice is retained in
post-embargo publicly released Xen Project advisories, even though it
is then no longer applicable.  This is to enable the community to have
oversight of the Xen Project Security Team's decisionmaking.)

For more information about permissible uses of embargoed information,
consult the Xen Project community's agreed Security Policy:
  http://www.xenproject.org/security-policy.html
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