We have just published Qubes Security Bulletin (QSB) 065: Missed flush in XSA-321 backport (XSA-366). The text of this QSB is reproduced below. This QSB and its accompanying signatures will always be available in the Qubes Security Pack (qubes-secpack).

View QSB-065 in the qubes-secpack:

https://github.com/QubesOS/qubes-secpack/blob/master/QSBs/qsb-065-2021.txt

Learn about the qubes-secpack, including how to obtain, verify, and read it:

https://www.qubes-os.org/security/pack/

View all past QSBs:

https://www.qubes-os.org/security/bulletins/

View XSA-366 in the XSA Tracker:

https://www.qubes-os.org/security/xsa/#366



             ---===[ Qubes Security Bulletin 065 ]===---

                             2021-02-18


              Missed flush in XSA-321 backport (XSA-366)


User action required
=====================

Users must install the following specific packages in order to address
the issues discussed in this bulletin:

  For Qubes 4.0:
  - Xen packages, versions 4.8.5-30

  For Qubes 4.1: not affected

The packages are to be installed in dom0 via the Qube Manager or via
the qubes-dom0-update command as follows:

  For updates from the stable repository (not immediately available):
  $ sudo qubes-dom0-update

  For updates from the security-testing repository:
  $ sudo qubes-dom0-update --enablerepo=qubes-dom0-security-testing

A system restart will be required afterwards.

These packages will migrate from the security-testing repository to the
current (stable) repository over the next two weeks after being tested
by the community.

If you use Anti Evil Maid, you will need to reseal your secret
passphrase to new PCR values, as PCR18+19 will change due to the new
Xen binaries.


Summary
========

On 2021-02-18, the Xen Security Team published the following Xen
Security Advisory (XSA):

XSA-366 [1] "missed flush in XSA-321 backport"
| An oversight was made when backporting XSA-320, leading entries in the
| IOMMU not being properly updated under certain circumstances.



Impact
=======

XSA-366, as described by the Xen Security Team:
| A malicious guest may be able to retain read/write DMA access to
| frames returned to Xen's free pool, and later reused for another
| purpose.  Host crashes (leading to a Denial of Service) and privilege
| escalation cannot be ruled out.


Credits
========

See the original Xen Security Advisory.


References
===========

[1] https://xenbits.xen.org/xsa/advisory-366.html

--
The Qubes Security Team
https://www.qubes-os.org/security/